Two Drive Failure on RAID-5

Two Drive Failure on RAID-5

[Cry]

Folks,

I had a drive fail on my 6 drive raid-5 array.  while syncing in the replacement
drive (11 percent complete) a second drive went bad.

Any suggestions to recover as much data as possible from the array?

Joel

Re: Two Drive Failure on RAID-5

[David Greaves]

Yep. Don't panic and don't do anything else yet if you're not confident about
what you're doing.

I'll follow up with more info in a short while.

Info you can provide:
kernel version
mdadm version
cat /proc/mdstat
mdadm --examine /dev/sd[abcdef]1 (or whatever your array components are)
relevant smartctl info on the bad drive(s)
dmesg info about the drive failures

Assuming genuine hardware failure:
Do you have any spare drives that you can use to replace the components?

David


Cry wrote:
> Folks,
> 
> I had a drive fail on my 6 drive raid-5 array.  while syncing in the replacement
> drive (11 percent complete) a second drive went bad.
> 
> Any suggestions to recover as much data as possible from the array?
> 
> Joel
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Two Drive Failure on RAID-5

[Cry]

David Greaves <david <at> dgreaves.com> writes:

> 
> Yep. Don't panic and don't do anything else yet if you're not confident about
> what you're doing.
> 
> I'll follow up with more info in a short while.
> 
> Info you can provide:
> kernel version
> mdadm version
> cat /proc/mdstat
> mdadm --examine /dev/sd[abcdef]1 (or whatever your array components are)
> relevant smartctl info on the bad drive(s)
> dmesg info about the drive failures
> 
> Assuming genuine hardware failure:
> Do you have any spare drives that you can use to replace the components?
> 
> David

Thanks for the info.  I was able to do a --force --assemble on the array and I
copied off my most critical data.  At the moment, I don't have enough drives to
take all the data on the array, so I'm going to be at a bit of a standstill
until new hardware arrives.

Since the copy of that data (about 500Gig of about 2TB) went so well, I decided
to try to sync up the spare again and it died at the same point and the raid
system pulled down the array.  I'm trying to decide if I should follow your
suggestion in sister post to copy the failed drive onto my spare or if I should
just format the spare and try to recover another 500 gig of data of the array.

Is there a mdadm or other command to tell the raid system to stay up in the face
of errors?  Can the array be assembled in a way that doesn't change the array in
any way (completely read-only)?

I've got the older failed drive also (about 15 hours older).  Can that be
leveraged also?

The server isn't networked right now, but I'll try to get the above requested
logs tonight.

By the way, I'm thinking about buying five of these:

Seagate Barracuda 7200.11 1TB ST31000340AS SATA-II 32MB Cache

and one of these:

Supermicro SUPERMICRO CSE-M35T-1 Hot-Swapable SATA HDD Enclosure

http://www.supermicro.com/products/accessories/mobilerack/CSE-M35T-1.cfm

and building a raid-6 array.  I'll convert the surviving drives into a backup
for the primary array.  Any feedback on the above?  Is there a suggestion on an
inexpensive controller to give more SATA ports that is very software raid
compatible?

Any suggestions for optimal configuration (ext3) and tuning for the new array? 
My load consists of serving a photo gallery via apache and gallery2 as well as a
local media (audio/video) server so files sizes tend to be large.

Thanks,

Joel

RE: Re: Two Drive Failure on RAID-5

[David Lethe]

-----Original Message-----
From: linux-raid-owner@vger.kernel.org
[mailto:linux-raid-owner@vger.kernel.org] On Behalf Of Cry
Sent: Tuesday, May 20, 2008 10:32 AM
To: linux-raid@vger.kernel.org
Subject: Re: Two Drive Failure on RAID-5

David Greaves <david <at> dgreaves.com> writes:

> 
> Yep. Don't panic and don't do anything else yet if you're not
confident about
> what you're doing.
> 
> I'll follow up with more info in a short while.
> 
> Info you can provide:
> kernel version
> mdadm version
> cat /proc/mdstat
> mdadm --examine /dev/sd[abcdef]1 (or whatever your array components
are)
> relevant smartctl info on the bad drive(s)
> dmesg info about the drive failures
> 
> Assuming genuine hardware failure:
> Do you have any spare drives that you can use to replace the
components?
> 
> David

Thanks for the info.  I was able to do a --force --assemble on the array
and I
copied off my most critical data.  At the moment, I don't have enough
drives to
take all the data on the array, so I'm going to be at a bit of a
standstill
until new hardware arrives.

Since the copy of that data (about 500Gig of about 2TB) went so well, I
decided
to try to sync up the spare again and it died at the same point and the
raid
system pulled down the array.  I'm trying to decide if I should follow
your
suggestion in sister post to copy the failed drive onto my spare or if I
should
just format the spare and try to recover another 500 gig of data of the
array.

Is there a mdadm or other command to tell the raid system to stay up in
the face
of errors?  Can the array be assembled in a way that doesn't change the
array in
any way (completely read-only)?

I've got the older failed drive also (about 15 hours older).  Can that
be
leveraged also?

The server isn't networked right now, but I'll try to get the above
requested
logs tonight.

By the way, I'm thinking about buying five of these:

Seagate Barracuda 7200.11 1TB ST31000340AS SATA-II 32MB Cache

and one of these:

Supermicro SUPERMICRO CSE-M35T-1 Hot-Swapable SATA HDD Enclosure

http://www.supermicro.com/products/accessories/mobilerack/CSE-M35T-1.cfm

and building a raid-6 array.  I'll convert the surviving drives into a
backup
for the primary array.  Any feedback on the above?  Is there a
suggestion on an
inexpensive controller to give more SATA ports that is very software
raid
compatible?

Any suggestions for optimal configuration (ext3) and tuning for the new
array? 
My load consists of serving a photo gallery via apache and gallery2 as
well as a
local media (audio/video) server so files sizes tend to be large.

Thanks,

Joel
===============
Joel:

Respectfully .. are you nuts??? 

Don't buy the 7200.11 disks.   You bought a bunch of desktop class
drives, and they crapped out on you, and you are about to make the same
mistake again.  Get the server class disk that is designed to run 24x7
duty cycle, which in your case would be the 'cuda ES.2

Sorry about the soapbox, but it never ceases to amaze me how people try
to save by buying disk drives architected with lowest possible cost in
mind, and don't investigate the higher-quality disks that are designed
for extended reliability and data integrity.

David

Re: Re: Two Drive Failure on RAID-5

[Cry]

David Lethe <david <at> santools.com> writes:

> Cry wrote:
>> By the way, I'm thinking about buying five of these:
>> 
>> Seagate Barracuda 7200.11 1TB ST31000340AS SATA-II 32MB Cache
>> 
>> and one of these:
>> 
>> Supermicro SUPERMICRO CSE-M35T-1 Hot-Swapable SATA HDD Enclosure
>> 
>> http://www.supermicro.com/products/accessories/mobilerack/CSE-M35T-1.cfm
>>
>> Any feedback on the above?  Is there a suggestion on an
>> inexpensive controller to give more SATA ports that is very software
>> raid compatible?
> 
> Respectfully .. are you nuts??? 

Probably, thats why I asked for a sanity check.

I had originally gotten a batch of six extremely inexpensive WD 500GB drives.  I
have now had 4 of those six drives go tango uniform since May of 07.  None of
the replacement drives I've purchased (samsung, hitachi) have reported even a
single SMART error.  For my personal systems these are the first drives I've had
crash in 20 years.

> Don't buy the 7200.11 disks.   You bought a bunch of desktop class
> drives, and they crapped out on you, and you are about to make the same
> mistake again.  Get the server class disk that is designed to run 24x7
> duty cycle, which in your case would be the 'cuda ES.2

If I go with the 'cuda ES.2 is that enough risk management to stick with a
raid-5 arrangement?  I am doing this on my own dime so if I can go with four
drives now instead of five it would pay for the increased drive grade.  

> Sorry about the soapbox, but it never ceases to amaze me how people try
> to save by buying disk drives architected with lowest possible cost in
> mind, and don't investigate the higher-quality disks that are designed
> for extended reliability and data integrity.

That is the RAID meme.  If you have the redundancy why spend money on the fancy
drives?  On the other hand, four drives crashing has cost me about $500 dollars
in replacement drives and lots of time.

Always looking for an angle ;-)

RE: Re: Re: Two Drive Failure on RAID-5

[David Lethe]

Here is a good analogy that puts this in perspective.  I haven't seen
anybody equate the two yet, so get the name right if you quote this ;)

Disk drives are like light bulbs. You can buy the server class (similar
to CFLs), or desktop (incandescent).  If you don't mind the dark,
replace them as they fail, and buy spares as they go on sale.
Conversely, if you have to maintain a vaulted ceiling chandelier, and
are afraid of heights, then spending twice as much for never having to
deal with *THAT* again will seem like a bargain.

- David Lethe



-----Original Message-----
From: linux-raid-owner@vger.kernel.org
[mailto:linux-raid-owner@vger.kernel.org] On Behalf Of Cry
Sent: Tuesday, May 20, 2008 2:01 PM
To: linux-raid@vger.kernel.org
Subject: Re: Re: Two Drive Failure on RAID-5

David Lethe <david <at> santools.com> writes:

> Cry wrote:
>> By the way, I'm thinking about buying five of these:
>> 
>> Seagate Barracuda 7200.11 1TB ST31000340AS SATA-II 32MB Cache
>> 
>> and one of these:
>> 
>> Supermicro SUPERMICRO CSE-M35T-1 Hot-Swapable SATA HDD Enclosure
>> 
>>
http://www.supermicro.com/products/accessories/mobilerack/CSE-M35T-1.cfm
>>
>> Any feedback on the above?  Is there a suggestion on an
>> inexpensive controller to give more SATA ports that is very software
>> raid compatible?
> 
> Respectfully .. are you nuts??? 

Probably, thats why I asked for a sanity check.

I had originally gotten a batch of six extremely inexpensive WD 500GB
drives.  I
have now had 4 of those six drives go tango uniform since May of 07.
None of
the replacement drives I've purchased (samsung, hitachi) have reported
even a
single SMART error.  For my personal systems these are the first drives
I've had
crash in 20 years.

> Don't buy the 7200.11 disks.   You bought a bunch of desktop class
> drives, and they crapped out on you, and you are about to make the
same
> mistake again.  Get the server class disk that is designed to run 24x7
> duty cycle, which in your case would be the 'cuda ES.2

If I go with the 'cuda ES.2 is that enough risk management to stick with
a
raid-5 arrangement?  I am doing this on my own dime so if I can go with
four
drives now instead of five it would pay for the increased drive grade.  

> Sorry about the soapbox, but it never ceases to amaze me how people
try
> to save by buying disk drives architected with lowest possible cost in
> mind, and don't investigate the higher-quality disks that are designed
> for extended reliability and data integrity.

That is the RAID meme.  If you have the redundancy why spend money on
the fancy
drives?  On the other hand, four drives crashing has cost me about $500
dollars
in replacement drives and lots of time.

Always looking for an angle ;-)

--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

RE: Re: Re: Two Drive Failure on RAID-5

[Keith Roberts]

On Tue, 20 May 2008, David Lethe wrote:

> To: Cry <cry_regarder@yahoo.com>, linux-raid@vger.kernel.org
> From: David Lethe <david@santools.com>
> Subject: RE:  Re:  Re: Two Drive Failure on RAID-5
> 
> Here is a good analogy that puts this in perspective.  I haven't seen
> anybody equate the two yet, so get the name right if you quote this ;)
>
> Disk drives are like light bulbs. You can buy the server class (similar
> to CFLs), or desktop (incandescent).  If you don't mind the dark,
> replace them as they fail, and buy spares as they go on sale.
> Conversely, if you have to maintain a vaulted ceiling chandelier, and
> are afraid of heights, then spending twice as much for never having to
> deal with *THAT* again will seem like a bargain.
>
> - David Lethe

So are there such things as server class EIDE drives? Or are 
they all SCSI or SATA?

Keith

Re: Re: Two Drive Failure on RAID-5

[Janos Haar]

----- Original Message ----- 
From: "David Lethe" <david@santools.com>
To: "Cry" <cry_regarder@yahoo.com>; <linux-raid@vger.kernel.org>
Sent: Tuesday, May 20, 2008 7:18 PM
Subject: RE: Re: Two Drive Failure on RAID-5


>
>
> -----Original Message-----
> From: linux-raid-owner@vger.kernel.org
> [mailto:linux-raid-owner@vger.kernel.org] On Behalf Of Cry
> Sent: Tuesday, May 20, 2008 10:32 AM
> To: linux-raid@vger.kernel.org
> Subject: Re: Two Drive Failure on RAID-5
>
> David Greaves <david <at> dgreaves.com> writes:
>
>>
>> Yep. Don't panic and don't do anything else yet if you're not
> confident about
>> what you're doing.
>>
>> I'll follow up with more info in a short while.
>>
>> Info you can provide:
>> kernel version
>> mdadm version
>> cat /proc/mdstat
>> mdadm --examine /dev/sd[abcdef]1 (or whatever your array components
> are)
>> relevant smartctl info on the bad drive(s)
>> dmesg info about the drive failures
>>
>> Assuming genuine hardware failure:
>> Do you have any spare drives that you can use to replace the
> components?
>>
>> David
>
> Thanks for the info.  I was able to do a --force --assemble on the array
> and I
> copied off my most critical data.  At the moment, I don't have enough
> drives to
> take all the data on the array, so I'm going to be at a bit of a
> standstill
> until new hardware arrives.
>
> Since the copy of that data (about 500Gig of about 2TB) went so well, I
> decided
> to try to sync up the spare again and it died at the same point and the
> raid
> system pulled down the array.  I'm trying to decide if I should follow
> your
> suggestion in sister post to copy the failed drive onto my spare or if I
> should
> just format the spare and try to recover another 500 gig of data of the
> array.
>
> Is there a mdadm or other command to tell the raid system to stay up in
> the face
> of errors?  Can the array be assembled in a way that doesn't change the
> array in
> any way (completely read-only)?
>
> I've got the older failed drive also (about 15 hours older).  Can that
> be
> leveraged also?
>
> The server isn't networked right now, but I'll try to get the above
> requested
> logs tonight.
>
> By the way, I'm thinking about buying five of these:
>
> Seagate Barracuda 7200.11 1TB ST31000340AS SATA-II 32MB Cache
>
> and one of these:
>
> Supermicro SUPERMICRO CSE-M35T-1 Hot-Swapable SATA HDD Enclosure
>
> http://www.supermicro.com/products/accessories/mobilerack/CSE-M35T-1.cfm
>
> and building a raid-6 array.  I'll convert the surviving drives into a
> backup
> for the primary array.  Any feedback on the above?  Is there a
> suggestion on an
> inexpensive controller to give more SATA ports that is very software
> raid
> compatible?
>
> Any suggestions for optimal configuration (ext3) and tuning for the new
> array?
> My load consists of serving a photo gallery via apache and gallery2 as
> well as a
> local media (audio/video) server so files sizes tend to be large.
>
> Thanks,
>
> Joel
> ===============
> Joel:
>
> Respectfully .. are you nuts???
>
> Don't buy the 7200.11 disks.   You bought a bunch of desktop class
> drives, and they crapped out on you, and you are about to make the same
> mistake again.  Get the server class disk that is designed to run 24x7
> duty cycle, which in your case would be the 'cuda ES.2
>
> Sorry about the soapbox, but it never ceases to amaze me how people try
> to save by buying disk drives architected with lowest possible cost in
> mind, and don't investigate the higher-quality disks that are designed
> for extended reliability and data integrity.
>
> David

David and Joel,

Let me remember you to the power supply!
This is really important too!

The 24x7 cycle systems need a good quality PS and cables, connectors for 
hdd.
One poor (Y) cable, or connector can make easy 1-2 or more failed drives at 
a same time!
The SMART can monitor the actual state, but can not monitor the bad 
connection and/or noise on the voltage.

Cheers,
Janos


>
>
>
>
>
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html 

RE: Re: Two Drive Failure on RAID-5

[David Lethe]

-----Original Message-----
From: linux-raid-owner@vger.kernel.org
[mailto:linux-raid-owner@vger.kernel.org] On Behalf Of Cry
Sent: Tuesday, May 20, 2008 10:32 AM
To: linux-raid@vger.kernel.org
Subject: Re: Two Drive Failure on RAID-5

David Greaves <david <at> dgreaves.com> writes:

> 
> Yep. Don't panic and don't do anything else yet if you're not
confident about
> what you're doing.
> 
> I'll follow up with more info in a short while.
> 
> Info you can provide:
> kernel version
> mdadm version
> cat /proc/mdstat
> mdadm --examine /dev/sd[abcdef]1 (or whatever your array components
are)
> relevant smartctl info on the bad drive(s)
> dmesg info about the drive failures
> 
> Assuming genuine hardware failure:
> Do you have any spare drives that you can use to replace the
components?
> 
> David

Thanks for the info.  I was able to do a --force --assemble on the array
and I
copied off my most critical data.  At the moment, I don't have enough
drives to
take all the data on the array, so I'm going to be at a bit of a
standstill
until new hardware arrives.

Since the copy of that data (about 500Gig of about 2TB) went so well, I
decided
to try to sync up the spare again and it died at the same point and the
raid
system pulled down the array.  I'm trying to decide if I should follow
your
suggestion in sister post to copy the failed drive onto my spare or if I
should
just format the spare and try to recover another 500 gig of data of the
array.

Is there a mdadm or other command to tell the raid system to stay up in
the face
of errors?  Can the array be assembled in a way that doesn't change the
array in
any way (completely read-only)?

I've got the older failed drive also (about 15 hours older).  Can that
be
leveraged also?

The server isn't networked right now, but I'll try to get the above
requested
logs tonight.

By the way, I'm thinking about buying five of these:

Seagate Barracuda 7200.11 1TB ST31000340AS SATA-II 32MB Cache

and one of these:

Supermicro SUPERMICRO CSE-M35T-1 Hot-Swapable SATA HDD Enclosure

http://www.supermicro.com/products/accessories/mobilerack/CSE-M35T-1.cfm

and building a raid-6 array.  I'll convert the surviving drives into a
backup
for the primary array.  Any feedback on the above?  Is there a
suggestion on an
inexpensive controller to give more SATA ports that is very software
raid
compatible?

Any suggestions for optimal configuration (ext3) and tuning for the new
array? 
My load consists of serving a photo gallery via apache and gallery2 as
well as a
local media (audio/video) server so files sizes tend to be large.

Thanks,

Joel

----------------
Also .. statistically speaking, you just lost 2 of 6 disks, within hours
of each other, and you have 4 more disks that had the same workload and
exposure to environmental conditions.  Assuming you deployed all 6 disks
at the same time, and they were all made at the same time, then you are
betting your data against those other 4 drives failing soon.  Make sure
you have current backup.

David

Re: Two Drive Failure on RAID-5

[Brad Campbell]

Cry wrote:
> 
> Supermicro SUPERMICRO CSE-M35T-1 Hot-Swapable SATA HDD Enclosure
> 
> http://www.supermicro.com/products/accessories/mobilerack/CSE-M35T-1.cfm
> 
> and building a raid-6 array.  I'll convert the surviving drives into a backup
> for the primary array.  Any feedback on the above?  Is there a suggestion on an
> inexpensive controller to give more SATA ports that is very software raid
> compatible?
> 

I've got 5 of those enclosures with Maxtor Maxline-II drives in them. I've had them all running 
between 3 & 4 years now and I've been *extremely* happy with the enclosures. The whole lot are 
running on 7 Promise SATA150TX4 cards. So I'd certainly be happy with the enclosures, however I tend 
to agree with what David said below about going for the higher grade drives. I paid a bit extra for 
the Maxline-II drives over the desktop grade disks, and I've got 27 of them with about 30,000 hours 
on them now. One early life failure (in the 1st 5 hours) and one recently replaced as it was growing 
defects.. but the 26 remaining drives are solid.

Oh, 15 drives are in a RAID-6 and 10 are in a RAID-5. I plan to replace the 10 drive RAID-5 with 10 
1TB drives in a RAID-6 in the not to distant future. I did have a dual drive failure on the RAID-6 
(not actually drive related, but a software glitch) and having the RAID-6 saved the data nicely.


Brad
-- 
"Human beings, who are almost unique in having the ability
to learn from the experience of others, are also remarkable
for their apparent disinclination to do so." -- Douglas Adams

Re: Two Drive Failure on RAID-5

[David Greaves]

Cry wrote:
> Folks,
> 
> I had a drive fail on my 6 drive raid-5 array.  while syncing in the replacement
> drive (11 percent complete) a second drive went bad.
> 
> Any suggestions to recover as much data as possible from the array?

Let us know if any step fails...

How valuable is your data - if it is very valuable and you have no backups then
you may want to seek professional help.

The replacement drive *may* help to rebuild up to 11% of your data in the event
that the bad drive fails completely. You can keep it to one side to try this if
you get really desperate.

Assuming a real drive hardware failure (smartctl shows errors and dmesg showed
media errors or similar).

I would first suggest using ddrescue to duplicate the 2nd failed drive onto a
spare drive (the replacement is fine if you want to risk that <11% of
potentially saved data - a new drive would be better - you're going to need a
new one anyway!)

SOURCE is the 2nd failed drive
TARGET is it's replacement

blockdev --getra /dev/SOURCE <note the readahead value>
blockdev --setro /dev/SOURCE
blockdev --setra  0 /dev/SOURCE
ddrescue /dev/SOURCE /dev/TARGET /somewhere_safe/logfile

Note, Janos Haar recently (18/may) posted a more conservative approach that you
may want to use. Additionally you may want to use a logfile

ddrescue lets you know how much data it failed to recover. If this is a lot then
you may want to read up on the ddrescue info page (includes a tutorial and lots
of explanation) and consider drive data recovery tricks such as drive cooling
(which some sources suggest may cause more damage than they solve but has worked
for me in the past).

I have also left ddrescue running overnight against a system that repeatedly
timed-out and in the morning I've had a *lot* more recovered data.

Having *successfully* done that you can re-assemble the array using the 4 good
disks and the newly duplicated one.

unless you've rebooted:
blockdev --setrw /dev/SOURCE
blockdev --setra  <saved readahead value> /dev/SOURCE

mdadm --assemble --force /dev/md0 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1

cat /proc/mdstat will show the drive status
mdadm --detail /dev/md0
mdadm --examine /dev/sd[abcdef]1 [components]

Should all show a reasonably healthy but degraded array.

This should now be amenable to a read-only fsck/xfs_repair/whatever.

If that looks reasonable then you may want to do a proper fsck, perform a backup
and add a new drive.

HTH - let me know if any steps don't make sense; I think its about time I put
something on the wiki about data-recovery...

David

Re: Two Drive Failure on RAID-5

[Janos Haar]

----- Original Message ----- 
From: "David Greaves" <david@dgreaves.com>
To: "Cry" <cry_regarder@yahoo.com>
Cc: <linux-raid@vger.kernel.org>
Sent: Tuesday, May 20, 2008 11:14 AM
Subject: Re: Two Drive Failure on RAID-5


> Cry wrote:
>> Folks,
>>
>> I had a drive fail on my 6 drive raid-5 array.  while syncing in the 
>> replacement
>> drive (11 percent complete) a second drive went bad.
>>
>> Any suggestions to recover as much data as possible from the array?
>
> Let us know if any step fails...
>
> How valuable is your data - if it is very valuable and you have no backups 
> then
> you may want to seek professional help.
>
> The replacement drive *may* help to rebuild up to 11% of your data in the 
> event
> that the bad drive fails completely. You can keep it to one side to try 
> this if
> you get really desperate.
>
> Assuming a real drive hardware failure (smartctl shows errors and dmesg 
> showed
> media errors or similar).
>
> I would first suggest using ddrescue to duplicate the 2nd failed drive 
> onto a
> spare drive (the replacement is fine if you want to risk that <11% of
> potentially saved data - a new drive would be better - you're going to 
> need a
> new one anyway!)
>
> SOURCE is the 2nd failed drive
> TARGET is it's replacement
>
> blockdev --getra /dev/SOURCE <note the readahead value>
> blockdev --setro /dev/SOURCE
> blockdev --setra  0 /dev/SOURCE
> ddrescue /dev/SOURCE /dev/TARGET /somewhere_safe/logfile
>
> Note, Janos Haar recently (18/may) posted a more conservative approach 
> that you
> may want to use. Additionally you may want to use a logfile
>
> ddrescue lets you know how much data it failed to recover. If this is a 
> lot then
> you may want to read up on the ddrescue info page (includes a tutorial and 
> lots
> of explanation) and consider drive data recovery tricks such as drive 
> cooling
> (which some sources suggest may cause more damage than they solve but has 
> worked
> for me in the past).
>
> I have also left ddrescue running overnight against a system that 
> repeatedly
> timed-out and in the morning I've had a *lot* more recovered data.
>
> Having *successfully* done that you can re-assemble the array using the 4 
> good
> disks and the newly duplicated one.
>
> unless you've rebooted:
> blockdev --setrw /dev/SOURCE
> blockdev --setra  <saved readahead value> /dev/SOURCE
>
> mdadm --assemble --force /dev/md0 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1 
> /dev/sde1
>
> cat /proc/mdstat will show the drive status
> mdadm --detail /dev/md0
> mdadm --examine /dev/sd[abcdef]1 [components]
>
> Should all show a reasonably healthy but degraded array.
>
> This should now be amenable to a read-only fsck/xfs_repair/whatever.

Maybe COW loop helps a lot. ;-)

>
> If that looks reasonable then you may want to do a proper fsck, perform a 
> backup
> and add a new drive.
>
> HTH - let me know if any steps don't make sense; I think its about time I 
> put
> something on the wiki about data-recovery...
>
> David
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html 

Re: Two Drive Failure on RAID-5

[Cry]

David Greaves <david <at> dgreaves.com> writes:
> 
> Cry wrote:
>> Folks,
>> 
>> I had a drive fail on my 6 drive raid-5 array.  while syncing in the 
>> replacement
>> drive (11 percent complete) a second drive went bad.
>> 
>
> blockdev --getra /dev/SOURCE <note the readahead value>
> blockdev --setro /dev/SOURCE
> blockdev --setra  0 /dev/SOURCE
> ddrescue /dev/SOURCE /dev/TARGET /somewhere_safe/logfile
> 
 
> unless you've rebooted:
> blockdev --setrw /dev/SOURCE
> blockdev --setra  <saved readahead value> /dev/SOURCE
> 
> mdadm --assemble --force /dev/md0 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1
> /dev/sde1
 
> cat /proc/mdstat will show the drive status
> mdadm --detail /dev/md0
> mdadm --examine /dev/sd[abcdef]1 [components]

I performed the above steps, however I used dd_rescue instead of ddrescue.

]# dd_rescue -l sda_rescue.log -o sda_rescue.bad -v /dev/sda /dev/sdg1 

dd_rescue: (info): about to transfer 0.0 kBytes from /dev/sda to /dev/sdg1
dd_rescue: (info): blocksizes: soft 65536, hard 512
dd_rescue: (info): starting positions: in 0.0k, out 0.0k
dd_rescue: (info): Logfile: sda_rescue.log, Maxerr: 0
dd_rescue: (info): Reverse: no , Trunc: no , interactive: no 
dd_rescue: (info): abort on Write errs: no , spArse write: if err

.......

dd_rescue: (info): /dev/sda (488386592.0k): EOF
Summary for /dev/sda -> /dev/sdg1:
dd_rescue: (info): ipos: 488386592.0k, opos: 488386592.0k, 
  xferd: 488386592.0k
                   errs:    504, errxfer:       252.0k, 
  succxfer: 488386336.0k
             +curr.rate:    47904kB/s, avg.rate:    14835kB/s, 
  avg.load:  9.6%


/dev/sdg1 is my replacement drive (750G) that I had tried to sync
previously.  The problem now is that while the copy happened, mdadm 
still thinks it is that old spare:

~]#  mdadm -E /dev/sdg1 /dev/sda
/dev/sdg1:
          Magic : a92b4efc
        Version : 00.90.00
           UUID : 18e3d0b8:a21b31d2:7216c3e5:9bbd9f39
  Creation Time : Thu May 24 01:55:48 2007
     Raid Level : raid5
  Used Dev Size : 488386432 (465.76 GiB 500.11 GB)
     Array Size : 2441932160 (2328.81 GiB 2500.54 GB)
   Raid Devices : 6
  Total Devices : 6
Preferred Minor : 0

    Update Time : Mon May 19 22:32:56 2008
          State : clean
 Active Devices : 4
Working Devices : 5
 Failed Devices : 2
  Spare Devices : 1
       Checksum : 1dc8dcfa - correct
         Events : 0.1187802

         Layout : left-symmetric
     Chunk Size : 128K

      Number   Major   Minor   RaidDevice State
this     6       8       97        6      spare   /dev/sdg1

   0     0       8       80        0      active sync   /dev/sdf
   1     1       8       64        1      active sync   /dev/sde
   2     2       8      128        2      active sync   /dev/sdi
   3     3       0        0        3      faulty removed
   4     4       0        0        4      faulty removed
   5     5       8      144        5      active sync   /dev/sdj
   6     6       8       97        6      spare   /dev/sdg1
/dev/sda:
          Magic : a92b4efc
        Version : 00.90.00
           UUID : 18e3d0b8:a21b31d2:7216c3e5:9bbd9f39
  Creation Time : Thu May 24 01:55:48 2007
     Raid Level : raid5
  Used Dev Size : 488386432 (465.76 GiB 500.11 GB)
     Array Size : 2441932160 (2328.81 GiB 2500.54 GB)
   Raid Devices : 6
  Total Devices : 6
Preferred Minor : 0

    Update Time : Mon May 19 21:40:13 2008
          State : clean
 Active Devices : 5
Working Devices : 6
 Failed Devices : 1
  Spare Devices : 1
       Checksum : 1dc8d023 - correct
         Events : 0.1187796

         Layout : left-symmetric
     Chunk Size : 128K

      Number   Major   Minor   RaidDevice State
this     4       8        0        4      active sync   /dev/sda

   0     0       8       80        0      active sync   /dev/sdf
   1     1       8       64        1      active sync   /dev/sde
   2     2       8      128        2      active sync   /dev/sdi
   3     3       0        0        3      faulty removed
   4     4       8        0        4      active sync   /dev/sda
   5     5       8      144        5      active sync   /dev/sdj
   6     6       8       97        6      spare   /dev/sdg1

and when I try to assemble the array, it only sees four disks 
plus a spare.

]# mdadm --assemble --force --verbose /dev/md0 /dev/sdf /dev/sde 
/dev/sdi /dev/sdj /dev/sdg1
mdadm: looking for devices for /dev/md0
mdadm: /dev/sdf is identified as a member of /dev/md0, slot 0.
mdadm: /dev/sde is identified as a member of /dev/md0, slot 1.
mdadm: /dev/sdi is identified as a member of /dev/md0, slot 2.
mdadm: /dev/sdj is identified as a member of /dev/md0, slot 5.
mdadm: /dev/sdg1 is identified as a member of /dev/md0, slot 6.
mdadm: added /dev/sde to /dev/md0 as 1
mdadm: added /dev/sdi to /dev/md0 as 2
mdadm: no uptodate device for slot 3 of /dev/md0
mdadm: no uptodate device for slot 4 of /dev/md0
mdadm: added /dev/sdj to /dev/md0 as 5
mdadm: added /dev/sdg1 to /dev/md0 as 6
mdadm: added /dev/sdf to /dev/md0 as 0
mdadm: /dev/md0 assembled from 4 drives and 1 spare - not enough to 
start the array.


How do I transfer the label from /dev/sda (no partitions) to /dev/sdg1?

Thanks,

Cry

Re: Two Drive Failure on RAID-5

[David Greaves]

Cry wrote:
> David Greaves <david <at> dgreaves.com> writes:
>> Cry wrote:
>> ddrescue /dev/SOURCE /dev/TARGET /somewhere_safe/logfile
>>
>  
>> unless you've rebooted:
>> blockdev --setrw /dev/SOURCE
>> blockdev --setra  <saved readahead value> /dev/SOURCE
>>
>> mdadm --assemble --force /dev/md0 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1
>> /dev/sde1
>  
>> cat /proc/mdstat will show the drive status
>> mdadm --detail /dev/md0
>> mdadm --examine /dev/sd[abcdef]1 [components]
> 
> I performed the above steps, however I used dd_rescue instead of ddrescue.
Similar software. I think dd_rescue is more 'scripted' and less maintained.

> ]# dd_rescue -l sda_rescue.log -o sda_rescue.bad -v /dev/sda /dev/sdg1

doh!!
You copied the disk (/dev/sda) into a partition (/dev/sdg1)...


> dd_rescue: (info): /dev/sda (488386592.0k): EOF
> Summary for /dev/sda -> /dev/sdg1:
> dd_rescue: (info): ipos: 488386592.0k, opos: 488386592.0k, 
>   xferd: 488386592.0k
>                    errs:    504, errxfer:       252.0k, 
>   succxfer: 488386336.0k
>              +curr.rate:    47904kB/s, avg.rate:    14835kB/s, 
>   avg.load:  9.6%
So you lost 252k of data. There may be filesystem corruption, a file may be
corrupt or some blank diskspace may be even more blank. Almost impossible to tell.

[aside: It would be nice if we could take the output from ddrescue and friends
to determine what the lost blocks map to via the md stripes.]

> /dev/sdg1 is my replacement drive (750G) that I had tried to sync
> previously.
No. /dev/sdg1 is a *partition* on your old drive.

I'm concerned that running the first ddrescue may have stressed /dev/sda and
you'd lose data running it again with the correct arguments.

> How do I transfer the label from /dev/sda (no partitions) to /dev/sdg1?
Can anyone suggest anything.

Cry don't do this...

I wonder about
 dd if=/dev/sdg1 of=/dev/sdg
but goodness knows if it would work... it'd rely on dd reading from the start of
the partition device and writes to the disk device not overlapping - which they
shouldn't but...

David

Re: Two Drive Failure on RAID-5

[Janos Haar]

----- Original Message ----- 
From: "David Greaves" <david@dgreaves.com>
To: "Cry" <cry_regarder@yahoo.com>
Cc: <linux-raid@vger.kernel.org>
Sent: Wednesday, May 21, 2008 10:15 PM
Subject: Re: Two Drive Failure on RAID-5


> Cry wrote:
>> David Greaves <david <at> dgreaves.com> writes:
>>> Cry wrote:
>>> ddrescue /dev/SOURCE /dev/TARGET /somewhere_safe/logfile
>>>
>>
>>> unless you've rebooted:
>>> blockdev --setrw /dev/SOURCE
>>> blockdev --setra  <saved readahead value> /dev/SOURCE
>>>
>>> mdadm --assemble --force /dev/md0 /dev/sda1 /dev/sdb1 /dev/sdc1 
>>> /dev/sdd1
>>> /dev/sde1
>>
>>> cat /proc/mdstat will show the drive status
>>> mdadm --detail /dev/md0
>>> mdadm --examine /dev/sd[abcdef]1 [components]
>>
>> I performed the above steps, however I used dd_rescue instead of 
>> ddrescue.
> Similar software. I think dd_rescue is more 'scripted' and less 
> maintained.
>
>> ]# dd_rescue -l sda_rescue.log -o sda_rescue.bad -v /dev/sda /dev/sdg1
>
> doh!!
> You copied the disk (/dev/sda) into a partition (/dev/sdg1)...
>
>
>> dd_rescue: (info): /dev/sda (488386592.0k): EOF
>> Summary for /dev/sda -> /dev/sdg1:
>> dd_rescue: (info): ipos: 488386592.0k, opos: 488386592.0k,
>>   xferd: 488386592.0k
>>                    errs:    504, errxfer:       252.0k,
>>   succxfer: 488386336.0k
>>              +curr.rate:    47904kB/s, avg.rate:    14835kB/s,
>>   avg.load:  9.6%
> So you lost 252k of data. There may be filesystem corruption, a file may 
> be
> corrupt or some blank diskspace may be even more blank. Almost impossible 
> to tell.

The dd_rescue shows if the target device is full.
The errs number divisible by 8, i think its only bad sectors.

But let me note:
With the default -b 64k, dd_rescue sometimes drop the entire soft block area 
on the first error!
If you want more precise result, run it again with -b 4096 and -B 1024, and 
if you can, don't copy the drive to the partition! :-)

>
> [aside: It would be nice if we could take the output from ddrescue and 
> friends
> to determine what the lost blocks map to via the md stripes.]
>
>> /dev/sdg1 is my replacement drive (750G) that I had tried to sync
>> previously.
> No. /dev/sdg1 is a *partition* on your old drive.
>
> I'm concerned that running the first ddrescue may have stressed /dev/sda 
> and
> you'd lose data running it again with the correct arguments.
>
>> How do I transfer the label from /dev/sda (no partitions) to /dev/sdg1?
> Can anyone suggest anything.

Cry i only have this idea:
dd_rescue -v -m 128k -r /dev/source -S 128k superblock.bin
losetup /dev/loop0 superblock.bin
mdadm --build -l linear --raid-devices=2 /dev/md1 /dev/sdg1 /dev/loop0

And the working raid member is /dev/md1. ;-)
But only for recovery!!!

(only idea, not tested.)

Cheers,
Janos

>
> Cry don't do this...
>
> I wonder about
> dd if=/dev/sdg1 of=/dev/sdg
> but goodness knows if it would work... it'd rely on dd reading from the 
> start of
> the partition device and writes to the disk device not overlapping - which 
> they
> shouldn't but...
>
> David
> --
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html 

Re: Two Drive Failure on RAID-5

[Cry]

Janos Haar <janos.haar <at> netcenter.hu> writes:

> But let me note:
> With the default -b 64k, dd_rescue sometimes drop the entire soft block area 
> on the first error!
> If you want more precise result, run it again with -b 4096 and -B 1024, and 
> if you can, don't copy the drive to the partition! 

Since I kept the bad blocks file from the dd_rescue run, can I 
just use that to have dd_rescue try to copy exactly the right 
blocks out?  This would avoid over stressing the drive?  Would 
it be best to have dd_rescue copy the blocks to a file and then 
use dd to write them onto /dev/sdg1 in the right place?

>> [aside: It would be nice if we could take the output from ddrescue and 
>> friends
>> to determine what the lost blocks map to via the md stripes.]

Yes, because I also have /dev/sdc which failed several hours 
before /dev/sda.  Between the two, everything should be 
recoverable, modulo low probability of the same block failing 
on both.  Is there a procedure to rebuild the lost stripes 
leveraging the other failed drive?

>>> /dev/sdg1 is my replacement drive (750G) that I had tried to sync
>>> previously.

>> No. /dev/sdg1 is a *partition* on your old drive.

Nope.  /dev/sda is my old drive.  It has NO partitions because I was 
retarded 1 year ago:

Folks, I made a mistake when I created my original raid array 
(there is a note about it in the archives of this group) that 
I built the array on the raw drives, not on partitions.  
/dev/sda IS the drive.  There is no /dev/sda1.  However, the 
replacement drive is a 750Gig (not 500 like the originals) so 
I built a partition on the drive of the correct size: /dev/sdg1.

> >> How do I transfer the label from /dev/sda (no partitions) to /dev/sdg1?
> > Can anyone suggest anything.
> 
> Cry i only have this idea:
> dd_rescue -v -m 128k -r /dev/source -S 128k superblock.bin
> losetup /dev/loop0 superblock.bin
> mdadm --build -l linear --raid-devices=2 /dev/md1 /dev/sdg1 /dev/loop0
> 
> And the working raid member is /dev/md1. 
> But only for recovery!!!

Let me think about the above.  This will copy the information that mdadm -E gets
from the entire drive /dev/sda into the partition /dev/sdg1?

Also, I ordered:

SUPERMICRO CSE-M35T-1 Hot-Swapable SATA HDD Enclosure

and 5

Seagate Barracuda ES.2 ST31000340NS 1TB 7200 RPM SATA 3.0Gb/s Hard Drive

drives to build a RAID-6 replacement for my old array.  I'm 
planning on turning the old drives into a LVM or RAID-0 set 
to serve as a backup to the primary array.  Any suggestions 
for configuring the array (performance parameters etc.)?  
Given my constraints about getting this all working again, 
I can't go through a real performance testing loop.

Thanks,

Cry

Re: Two Drive Failure on RAID-5

[David Greaves]

Cry wrote:
> Janos Haar <janos.haar <at> netcenter.hu> writes:
>>> No. /dev/sdg1 is a *partition* on your old drive.
> 
> Nope.  /dev/sda is my old drive.  It has NO partitions because I was 
> retarded 1 year ago:
> 
> Folks, I made a mistake when I created my original raid array 
> (there is a note about it in the archives of this group) that 
> I built the array on the raw drives, not on partitions.
That is not a 'problem' although it is not regarded as best practice.

> /dev/sda IS the drive.  There is no /dev/sda1.  However, the 
> replacement drive is a 750Gig (not 500 like the originals) so 
> I built a partition on the drive of the correct size: /dev/sdg1.
And you didn't think to mention this?
Maybe you thought it would be in the support file I keep for you?


When people offer suggestions they (or at least I) will probably form a picture
of what's going on - if you are going to throw tweaks into the mix then they may
throw us off. Mention them.

You have failed to answer some potentially relevant questions and, before you
get this array rebuilt you wandered off (on the same thread) into discussions
about what disk drives you might like to buy, the best type of external
enclosure and various other oddments. This is not helpful.

>The correct information should already be in /dev/sdg1 since I copied the entire
>/dev/sda there (probably overwrote stuff in /dev/sdg2 since /dev/sda was 160K
>bigger than /dev/sdg1).
Err, no. Linux doesn't randomly overwrite other partitions...

You're on 0.9 superblocks which are located at the end of the disk.

I *think* your assemble problem is that /dev/sdg1 was an old component (slot 6);
it had a superblock near the end of the partition which you didn't zero. You
copied most of /dev/sda into it but you made /dev/sdg1 too small by a few k. The
copy finished before it copied the /dev/sda superblock (I don't know why it
didn't overwrite the old superblock??). Also, at some point, md will try and
seek past the end of /dev/sdg1 and will die.

You have now dug a maze of twisty passages...

I think at this point you should enlarge /dev/sdg1, recopy /dev/sda to /dev/sdg1
and try again. That will probably work.

David

Re: Two Drive Failure on RAID-5

[Cry]

David Greaves <david <at> dgreaves.com> writes:

> Cry wrote:
>> Janos Haar <janos.haar <at> netcenter.hu> writes:
>> 
>> Folks, I made a mistake when I created my original raid array 
>> (there is a note about it in the archives of this group) that 
>> I built the array on the raw drives, not on partitions.
> 
> When people offer suggestions they (or at least I) will probably form
> a picture of what's going on - if you are going to throw tweaks into 
> the mix then they may throw us off. Mention them.

Point taken.

> You have failed to answer some potentially relevant questions and, 
> before you get this array rebuilt you wandered off (on the same 
> thread) into discussions about what disk drives you might like to 
> buy, the best type of external enclosure and various other oddments. 
> This is not helpful.

Yup, I should have put that stuff into a separate thread.  That said, I
did get good feedback on those questions on the other branch of the thread.

> You're on 0.9 superblocks which are located at the end of the disk.

Thanks for the above line.  It was key.
 
> You have now dug a maze of twisty passages...

:-)
 
> I think at this point you should enlarge /dev/sdg1, recopy /dev/sda to
> /dev/sdg1 and try again. That will probably work.

What I ended up doing was writing off the extra 250G in /dev/sdg and using
ddrescue to copy the failed drive to it.

ddrescue -dr3 /dev/sdf /dev/sdg 750_ddrescue.log
Press Ctrl-C to interrupt
Initial status (read from logfile)
rescued:   500107 MB,  errsize:    356 kB,  errors:      72
Current status
rescued:   500107 MB,  errsize:   48128 B,  current rate:        0 B/s
   ipos:   482042 MB,   errors:      79,    average rate:      269 B/s
   opos:   482042 MB
Copying bad blocks... Retry 1

It was nice that ddrescue as invoked got a good chunk more off the drive
than I'd gotten with dd_rescue.

The interesting thing was that mdadm -E /dev/sdg reported that there wasn't
a superblock on it!  Then I remembered your note above about where the
superblocks are located so I figured that the data was all fine, just that the
superblock was in the wrong place.  So I let mdadm assemble the array:

At this point, I have moved the drives around extensively so drive letters
do not match earlier posts:

mdadm --create /dev/md0 --verbose --level=5 --raid-devices=6 --chunk=128
/dev/sdl /dev/sdi /dev/sdj missing /dev/sdg /dev/sdk

mdadm: layout defaults to left-symmetric
mdadm: /dev/sdl appears to be part of a raid array:
    level=raid5 devices=6 ctime=Thu May 24 01:55:48 2007
mdadm: /dev/sdi appears to be part of a raid array:
    level=raid5 devices=6 ctime=Thu May 24 01:55:48 2007
mdadm: /dev/sdj appears to be part of a raid array:
    level=raid5 devices=6 ctime=Thu May 24 01:55:48 2007
mdadm: /dev/sdk appears to be part of a raid array:
    level=raid5 devices=6 ctime=Thu May 24 01:55:48 2007
mdadm: size set to 488386432K
mdadm: largest drive (/dev/sdg) exceed size (488386432K) by more than 1%
Continue creating array? yes
mdadm: array /dev/md0 started.

At this point I was able to recover all but a couple files onto a second
raid array.  

Thanks David Greaves and Janos Haar for the wonderful advice on restoring
my data.  Thanks to David Lethe for the advice to get the server class 
drives and thanks to Brad Campbell for endorsing the supermicro CSE-M35T
enclosure.  It was quite easy to install and seems to be working well and
keeping the drives nice and cool.

The old and the new arrays:

md0 : active raid5 sdk[5] sdg[4] sdj[2] sdi[1] sdl[0]
      2441932160 blocks level 5, 128k chunk, algorithm 2 [6/5] [UUU_UU]
      
md1 : active raid6 sdd1[3] sdc1[2] sde1[4] sda1[0] sdb1[1]
      2930279808 blocks level 6, 128k chunk, algorithm 2 [5/5] [UUUUU]
      
Thanks again,

Cry

Re: Two Drive Failure on RAID-5

[Cry]

Janos Haar <janos.haar <at> netcenter.hu> writes:

> Cry i only have this idea:
> dd_rescue -v -m 128k -r /dev/source -S 128k superblock.bin
> losetup /dev/loop0 superblock.bin
> mdadm --build -l linear --raid-devices=2 /dev/md1 /dev/sdg1 /dev/loop0

Janos,

The correct information should already be in /dev/sdg1 since I copied the entire
/dev/sda there (probably overwrote stuff in /dev/sdg2 since /dev/sda was 160K
bigger than /dev/sdg1).

This means I the superblock should already be there at the start of /dev/sdg1.
so the steps above should result in two superblocks being stacked back to back?

should I use an losetup offset into /dev/sdg1 to get to the real data and bypass
the MBR copied in from /dev/sda?  I am a bit confuse don how these things are
laid out.

Where on the disk does the information printed from mdadm -E /dev/sda and mdadm
-E /dev/sdg1 come from?

Thanks!

Cry

RE: Re: Re: Two Drive Failure on RAID-5

[David Lethe]

the disk manufacturers stopped making them last year, and stopped R&D on them way before that.  

-----Original Message-----

From:  "Keith Roberts" <keith@karsites.net>
Subj:  RE:  Re:  Re: Two Drive Failure on RAID-5
Date:  Tue May 20, 2008 5:20 pm
Size:  1K
To:  "linux-raid@vger.kernel.org" <linux-raid@vger.kernel.org>

On Tue, 20 May 2008, David Lethe wrote: 
 
> To: Cry <cry_regarder@yahoo.com>, linux-raid@vger.kernel.org 
> From: David Lethe <david@santools.com> 
> Subject: RE:  Re:  Re: Two Drive Failure on RAID-5 
>  
> Here is a good analogy that puts this in perspective.  I haven't seen 
> anybody equate the two yet, so get the name right if you quote this ;) 
> 
> Disk drives are like light bulbs. You can buy the server class (similar 
> to CFLs), or desktop (incandescent).  If you don't mind the dark, 
> replace them as they fail, and buy spares as they go on sale. 
> Conversely, if you have to maintain a vaulted ceiling chandelier, and 
> are afraid of heights, then spending twice as much for never having to 
> deal with *THAT* again will seem like a bargain. 
> 
> - David Lethe 
 
So are there such things as server class EIDE drives? Or are  
they all SCSI or SATA? 
 
Keith 
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To unsubscribe from this list: send the line "unsubscribe linux-raid" in 
the body of a message to majordomo@vger.kernel.org 
More majordomo info at  http://vger.kernel.org/majordomo-info.html 
 

Re: Two Drive Failure on RAID-5

[Ric Wheeler]

David Lethe wrote:
> the disk manufacturers stopped making them last year, and stopped R&D on them way before that.  
>
> -----Original Message-----
>
> From:  "Keith Roberts" <keith@karsites.net>
> Subj:  RE:  Re:  Re: Two Drive Failure on RAID-5
> Date:  Tue May 20, 2008 5:20 pm
> Size:  1K
> To:  "linux-raid@vger.kernel.org" <linux-raid@vger.kernel.org>
>
> On Tue, 20 May 2008, David Lethe wrote: 
>  
>   
>> To: Cry <cry_regarder@yahoo.com>, linux-raid@vger.kernel.org 
>> From: David Lethe <david@santools.com> 
>> Subject: RE:  Re:  Re: Two Drive Failure on RAID-5 
>>  
>> Here is a good analogy that puts this in perspective.  I haven't seen 
>> anybody equate the two yet, so get the name right if you quote this ;) 
>>
>> Disk drives are like light bulbs. You can buy the server class (similar 
>> to CFLs), or desktop (incandescent).  If you don't mind the dark, 
>> replace them as they fail, and buy spares as they go on sale. 
>> Conversely, if you have to maintain a vaulted ceiling chandelier, and 
>> are afraid of heights, then spending twice as much for never having to 
>> deal with *THAT* again will seem like a bargain. 
>>
>> - David Lethe 
>>     
>  
> So are there such things as server class EIDE drives? Or are  
> they all SCSI or SATA? 
>  
> Keith 
>   
Different vendors have different strategies around how to market their 
various drives - you have archival (think big, slow S-ATA for things 
like a Tivo), S-ATA drives that are consumer grade or slightly higher 
class drive like SAS (serial attached SCSI) and then the highest quality 
drives (Fibre channel).

You can get good results from all classes of drives, but you need to 
make sure that you periodically check them pro-actively for errors and 
try to repair them in place if possible. Also, make sure you get an 
updated kernel so we don't kick out drives that would be otherwise 
perfectly reasonable ;-)

ric

RE: Two Drive Failure on RAID-5

[David Lethe]

-----Original Message-----
From: Ric Wheeler [mailto:ricwheeler@gmail.com] 
Sent: Thursday, May 22, 2008 9:43 AM
To: David Lethe
Cc: Keith Roberts; linux-raid@vger.kernel.org
Subject: Re: Two Drive Failure on RAID-5

David Lethe wrote:
> the disk manufacturers stopped making them last year, and stopped R&D
on them way before that.  
>
> -----Original Message-----
>
> From:  "Keith Roberts" <keith@karsites.net>
> Subj:  RE:  Re:  Re: Two Drive Failure on RAID-5
> Date:  Tue May 20, 2008 5:20 pm
> Size:  1K
> To:  "linux-raid@vger.kernel.org" <linux-raid@vger.kernel.org>
>
> On Tue, 20 May 2008, David Lethe wrote: 
>  
>   
>> To: Cry <cry_regarder@yahoo.com>, linux-raid@vger.kernel.org 
>> From: David Lethe <david@santools.com> 
>> Subject: RE:  Re:  Re: Two Drive Failure on RAID-5 
>>  
>> Here is a good analogy that puts this in perspective.  I haven't seen

>> anybody equate the two yet, so get the name right if you quote this
;) 
>>
>> Disk drives are like light bulbs. You can buy the server class
(similar 
>> to CFLs), or desktop (incandescent).  If you don't mind the dark, 
>> replace them as they fail, and buy spares as they go on sale. 
>> Conversely, if you have to maintain a vaulted ceiling chandelier, and

>> are afraid of heights, then spending twice as much for never having
to 
>> deal with *THAT* again will seem like a bargain. 
>>
>> - David Lethe 
>>     
>  
> So are there such things as server class EIDE drives? Or are  
> they all SCSI or SATA? 
>  
> Keith 
>   
Different vendors have different strategies around how to market their 
various drives - you have archival (think big, slow S-ATA for things 
like a Tivo), S-ATA drives that are consumer grade or slightly higher 
class drive like SAS (serial attached SCSI) and then the highest quality

drives (Fibre channel).

You can get good results from all classes of drives, but you need to 
make sure that you periodically check them pro-actively for errors and 
try to repair them in place if possible. Also, make sure you get an 
updated kernel so we don't kick out drives that would be otherwise 
perfectly reasonable ;-)

ric

============
I must add a caveat to what Ric said.  Disks are designed to withstand
specific duty cycles as well as tolerance for errors and intelligence
when it comes to automated error recovery.

His statement is only valid up to the point your usage doesn't exceed
the workload that a specific disk was designed to tolerate.
Furthermore, the superior server class drives have significantly better
error recovery & management.  As such, they are less prone to having
errors for any given load. Read the specs & programming manuals for
specifics.

So, for any given load, you can purchase disk drives that will actually
generate FEWER errors .. which is a heck of a lot better than having to
pro-actively test & repair and deal with drives that kernels kick out.

That's why the disk manufacturers have 146 GB disks that retail for $150
to $1000 dollars. The difference is not as many have claimed, just the
physical interface. 

David