* big raid5 trouble
@ 2006-01-01 22:10 Czigola Gabor
2006-01-01 23:24 ` berk walker
0 siblings, 1 reply; 6+ messages in thread
From: Czigola Gabor @ 2006-01-01 22:10 UTC (permalink / raw)
To: linux-raid
Hello all!
I'm not sure, that is this the right place to ask such question, but I'm
in a big trouble with my RAID5 array.
My last chance to get any of the data back stored in this array, is to
"unspare" a spare disk, that is untouched since the removal.
I googled but can't find neither a documentation nor a specification where
and how the spare flag is stored on a disk. Can you please help me?
Thanks a lot.
--
Czigola, Gabor
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: big raid5 trouble
2006-01-01 22:10 big raid5 trouble Czigola Gabor
@ 2006-01-01 23:24 ` berk walker
2006-01-02 3:24 ` Czigola Gabor
0 siblings, 1 reply; 6+ messages in thread
From: berk walker @ 2006-01-01 23:24 UTC (permalink / raw)
To: Czigola Gabor; +Cc: linux-raid
Czigola Gabor wrote:
> Hello all!
>
> I'm not sure, that is this the right place to ask such question, but
> I'm in a big trouble with my RAID5 array.
>
> My last chance to get any of the data back stored in this array, is to
> "unspare" a spare disk, that is untouched since the removal.
>
> I googled but can't find neither a documentation nor a specification
> where and how the spare flag is stored on a disk. Can you please help me?
>
> Thanks a lot.
I don 't think that will help you, per se. Why do you say it is your
last chance? If you have n-1 disks OK, then you may be OK. If not, a
spare will not help. Can you tell us more?
b-
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: big raid5 trouble
2006-01-01 23:24 ` berk walker
@ 2006-01-02 3:24 ` Czigola Gabor
2006-01-02 11:41 ` berk walker
0 siblings, 1 reply; 6+ messages in thread
From: Czigola Gabor @ 2006-01-02 3:24 UTC (permalink / raw)
To: linux-raid
On Sun, 1 Jan 2006, berk walker wrote:
> I don 't think that will help you, per se. Why do you say it is your last
> chance? If you have n-1 disks OK, then you may be OK. If not, a spare will
> not help. Can you tell us more?
> b-
>
So there is a RAID5 array with 4 disks. I had a long power failure, and
during the boot sequence, I saw that the 4th disk got marked as non fresh.
I started the process that should bring the 4th disk back in the array,
but during this the 3th disk died. The 4th disk is now marked as spare.
Meanwhile a found the 4k superblock on the disk (strace mdadm -E), and I
got - from the source of mdadm - the exact location of the spare flag. But
I guess, I have to recalc the correct checksum of the new superblock.(?)
--
Czigola, Gabor
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: big raid5 trouble
2006-01-02 3:24 ` Czigola Gabor
@ 2006-01-02 11:41 ` berk walker
2006-01-02 14:46 ` Czigola Gabor
0 siblings, 1 reply; 6+ messages in thread
From: berk walker @ 2006-01-02 11:41 UTC (permalink / raw)
To: Czigola Gabor; +Cc: linux-raid
Czigola Gabor wrote:
> On Sun, 1 Jan 2006, berk walker wrote:
>
>> I don 't think that will help you, per se. Why do you say it is your
>> last chance? If you have n-1 disks OK, then you may be OK. If not, a
>> spare will not help. Can you tell us more?
>> b-
>>
>
> So there is a RAID5 array with 4 disks. I had a long power failure,
> and during the boot sequence, I saw that the 4th disk got marked as
> non fresh. I started the process that should bring the 4th disk back
> in the array, but during this the 3th disk died. The 4th disk is now
> marked as spare.
>
> Meanwhile a found the 4k superblock on the disk (strace mdadm -E), and
> I got - from the source of mdadm - the exact location of the spare
> flag. But I guess, I have to recalc the correct checksum of the new
> superblock.(?)
>
The "spare" disk would be just that, spare, like a spare tire for a car,
pressure is up, ready to go. Each drive contained unique information,
which could be reconstructed from the remaining n-1 drives. You now
have 1 drive "the spare" with no data, and an n-2 array. You will
probably lose data, though the 3rd disk might have had errors in an
unused area. You can FORCE the drives back into an array if things
aren't too trashed. I can not tell what is the safest way to do this,
but someone here may.
b-
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: big raid5 trouble
2006-01-02 11:41 ` berk walker
@ 2006-01-02 14:46 ` Czigola Gabor
2006-01-04 7:16 ` Mitchell Laks
0 siblings, 1 reply; 6+ messages in thread
From: Czigola Gabor @ 2006-01-02 14:46 UTC (permalink / raw)
To: berk walker; +Cc: linux-raid
On Mon, 2 Jan 2006, berk walker wrote:
> The "spare" disk would be just that, spare, like a spare tire for a car,
> pressure is up, ready to go. Each drive contained unique information, which
> could be reconstructed from the remaining n-1 drives. You now have 1 drive
> "the spare" with no data, and an n-2 array. You will probably lose data,
> though the 3rd disk might have had errors in an unused area. You can FORCE
> the drives back into an array if things aren't too trashed. I can not tell
> what is the safest way to do this, but someone here may.
> b-
Yes, but the spare disk is just logically spare, because it was in the
array just before everything got wrong. I mean the data is untouched on
it. If I force it (with editing the raw disk superblock) to get a normal
active disk, should it behave like before the cutoff, shouldn't it? Or
does the RAID mechanism erase/change anything else on the disk that makes
this process impossible?
--
Czigola Gabor
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: big raid5 trouble
2006-01-02 14:46 ` Czigola Gabor
@ 2006-01-04 7:16 ` Mitchell Laks
0 siblings, 0 replies; 6+ messages in thread
From: Mitchell Laks @ 2006-01-04 7:16 UTC (permalink / raw)
To: linux-raid
On Monday 02 January 2006 09:46 am, Czigola Gabor wrote:
>
> Yes, but the spare disk is just logically spare, because it was in the
> array just before everything got wrong. I mean the data is untouched on
> it. If I force it (with editing the raw disk superblock) to get a normal
> active disk, should it behave like before the cutoff, shouldn't it? Or
> does the RAID mechanism erase/change anything else on the disk that makes
> this process impossible?
I am very interested in your recovery process having gone through it myself a
number of times with hardware raid.
I would also like to see how one can "set the flag" to accept the "spare"
drive - into the array.
I hope the gurus here can tell us how to do it.
One thing you can do. Before you play with the data on your array, you can
back up the individual hard drives to truely spare drives. Here you can use
dd, or
dd with ignore error flags - see man page and google and dd_rescue man page or
dd_rescue or
dd_rescue with dd_rescue_help.
These amazing tools may even help with the "dead" drive. You can see what you
can rescue. I was able to save some substantial data using those tools in the
past. Beware that it may take a long time to back up a severly damaged disk
- thats why the tools were invented.
Then you can try different techniques with your status "frozen".
It is this kind of headache that switched me to raid1 ...
Good Luck
Mitchell Laks
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2006-01-04 7:16 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
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2006-01-01 22:10 big raid5 trouble Czigola Gabor
2006-01-01 23:24 ` berk walker
2006-01-02 3:24 ` Czigola Gabor
2006-01-02 11:41 ` berk walker
2006-01-02 14:46 ` Czigola Gabor
2006-01-04 7:16 ` Mitchell Laks
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