3-drive RAID1 for my low use home server?

3-drive RAID1 for my low use home server?

[Mark Knecht]

Hi,
   Just triple checking what I think I've learned here before I start
loading Gentoo. Parts are arriving and I'm staring to put them
together to build a combo low-use server (backups and MythTV) as well
as desktop for my wife. I can do anything up to 6 drives but want the
RAID to survive in the face of possibly two drive failure. This is all
low bandwidth stuff.

   I'm fairly focused at this point on doing RAID1 using 3 drives.
Unless I hear differently I believe a 3-drive RAID1 could survive 2
drive failures, and as well any single drive could be taken to another
machine or even placed in an external USB/eSATA drive container in the
event of some major motherboard failure. Is any of that incorrect?

   Also, along the way folks have mentioned hot spares but I'm not
seeing that a hot spare does much for RAID1. Am I incorrect about
that? Granted, I guess the rebuild starts automatically and maybe
that's worth it, but I'm thinking that mdadm can probably let me know
fairly quickly that I need to do some work. I've purchased 6 drives so
I'll have 2 or 3 spares around and I can do a hot spare but I don't
see the value in spinning the drive for a year burning power and
wearing the drive out vs. just putting it on the shelf and keeping it
in reserve for a rainy day.

   Off to start tearing into packaging. Thanks in advance again for
all the great info I've gotten so far.

Cheers,
Mark

Re: 3-drive RAID1 for my low use home server?

[Eric Shubert]

Mark Knecht wrote:
> Hi,
>    Just triple checking what I think I've learned here before I start
> loading Gentoo. Parts are arriving and I'm staring to put them
> together to build a combo low-use server (backups and MythTV) as well
> as desktop for my wife. I can do anything up to 6 drives but want the
> RAID to survive in the face of possibly two drive failure. This is all
> low bandwidth stuff.
> 
>    I'm fairly focused at this point on doing RAID1 using 3 drives.
> Unless I hear differently I believe a 3-drive RAID1 could survive 2
> drive failures, and as well any single drive could be taken to another
> machine or even placed in an external USB/eSATA drive container in the
> event of some major motherboard failure. Is any of that incorrect?

All sounds right to me. Just be sure that the array is defined with 3 
drives and no spares.

>    Also, along the way folks have mentioned hot spares but I'm not
> seeing that a hot spare does much for RAID1. Am I incorrect about
> that?

Right. The only thing it would buy you is a little write performance, 
but you'd lose a little read performance, and take a performance hit 
if/when one drive goes off.

> Granted, I guess the rebuild starts automatically and maybe
> that's worth it, but I'm thinking that mdadm can probably let me know
> fairly quickly that I need to do some work. I've purchased 6 drives so
> I'll have 2 or 3 spares around and I can do a hot spare but I don't
> see the value in spinning the drive for a year burning power and
> wearing the drive out vs. just putting it on the shelf and keeping it
> in reserve for a rainy day.

Just one thought here. There is a certain "infant mortality syndrome" 
that drives experience (according to google study). I would rotate 
drives from the shelf into service after a year or so, while they're 
still under warranty (assuming 3yr warranty). If the warranty period is 
less than 2yr, rotate them sooner.

NJoy!

-- 
-Eric 'shubes'

Re: 3-drive RAID1 for my low use home server?

[Mark Knecht]

On Wed, Mar 24, 2010 at 7:49 AM, Eric Shubert <ejs@shubes.net> wrote:
> Mark Knecht wrote:
>>
>> Hi,
>>   Just triple checking what I think I've learned here before I start
>> loading Gentoo. Parts are arriving and I'm staring to put them
>> together to build a combo low-use server (backups and MythTV) as well
>> as desktop for my wife. I can do anything up to 6 drives but want the
>> RAID to survive in the face of possibly two drive failure. This is all
>> low bandwidth stuff.
>>
>>   I'm fairly focused at this point on doing RAID1 using 3 drives.
>> Unless I hear differently I believe a 3-drive RAID1 could survive 2
>> drive failures, and as well any single drive could be taken to another
>> machine or even placed in an external USB/eSATA drive container in the
>> event of some major motherboard failure. Is any of that incorrect?
>
> All sounds right to me. Just be sure that the array is defined with 3 drives
> and no spares.
>
>>   Also, along the way folks have mentioned hot spares but I'm not
>> seeing that a hot spare does much for RAID1. Am I incorrect about
>> that?
>
> Right. The only thing it would buy you is a little write performance, but
> you'd lose a little read performance, and take a performance hit if/when one
> drive goes off.
>
>> Granted, I guess the rebuild starts automatically and maybe
>> that's worth it, but I'm thinking that mdadm can probably let me know
>> fairly quickly that I need to do some work. I've purchased 6 drives so
>> I'll have 2 or 3 spares around and I can do a hot spare but I don't
>> see the value in spinning the drive for a year burning power and
>> wearing the drive out vs. just putting it on the shelf and keeping it
>> in reserve for a rainy day.
>
> Just one thought here. There is a certain "infant mortality syndrome" that
> drives experience (according to google study). I would rotate drives from
> the shelf into service after a year or so, while they're still under
> warranty (assuming 3yr warranty). If the warranty period is less than 2yr,
> rotate them sooner.
>
> NJoy!
>
> --
> -Eric 'shubes'

Thanks Eric. I'll keep this in mind.

Other than the work involved in fixing things this is a home setup so
if it was down for a day or two it's not like a mission critical or
anything.

Also, the really critical coming from another machine that has two RAID's in it:

1) Main RAID is RAID0 using RAID class drives. (Lower reliability but
speed where I need it.)

2) Backup RAID in first machine is a 3 drive RAID 1.

3) This 2nd machine which also has RAID1 as we've been speaking aobut.

So, machine 1 runs RAID0 for work and then automatically backs up data
every few hours to a RAID1 internal to the same box. Once a day I will
then back up the machine 1 RAID1 to machine 2's RAID1 so I'm covered
twice. If one RAID1 does down then I can basically just fix it will
the other RAID1 keeps me safe.

Certainly, every so often I go offsite for even more protection.

Cheers,
Mark

Cheers,
Mark
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