Missing Drives

Missing Drives

[James Howells]

Hi everyone.

Fantastic job with the Linux mdadm tool but I've got a problem that I need 
some support with.

(Before you all ask, I've Googled this one to death, so please don't think of 
me as ignorant and blind).

Basically, I have a 5 disk RAID-5 array in an Addonics external enclosure. 
Each disk is 1TB in size. Since I am running it over USB, it's takes 3-3.5 
days to resync the disks if something goes pear-shaped.

Now, I don't think the software is at fault because I've had the drive 
replaced with a brand new disk and it's doing the exact same thing - 
drive /dev/sde loses it's partition data (the drive's superblock) and the md 
device's superblock. The data is unaffected since I only ever mount the 
device as read-only unless I need RW capability. I physically power the 
device down after unmounting the partition and stopping the array.

Whilst other people have had this problem of drives suddenly "losing 
everything", they have been able to recover, but I cannot keep my computer 
running for 3-3.5 days just to rebuild good data!

My question is:

Is it possible to copy the md superblock from one known good drive to another 
and assemble it as forced-clean?

It's easy enough to recreate the partition table with a simple:

dd if=/dev/sda of=/dev/sde count=1 bs=512

command but I believe the mdadm superblock lives at the end of the drive and 
if I could recreate that then I could at least recover from a failure of a 
known-good drive without needing a resync.

I'm looking into getting the RAID controller card (actually an eSATA 5-1 mini 
card) replaced or repaired but in the meantime, I am exploring all avenues.

This only happens on /dev/sde and not on any other device. Swapping hard 
drives around doesn't make any difference either - /dev/sde is perfectly 
readable. Clearly, though, I am not happy about building an array with a 
drive in that "cursed" slot since the loss of another drive in a RAID-5 would 
destroy everything stored on the array.

Any advice would be gratefully appreciated.

Regards,

James

PS. I'm running Debian Lenny 2.6.26-2-686 32-bit kernel with mdadm version 
2.6.7.2-3 (repackaged for Debian).

Re: Missing Drives

[Mark Knecht]

On Tue, Jul 20, 2010 at 5:29 PM, James Howells <james@howells.uk.net> wrote:
> Hi everyone.
>
> Fantastic job with the Linux mdadm tool but I've got a problem that I need
> some support with.
>
> (Before you all ask, I've Googled this one to death, so please don't think of
> me as ignorant and blind).
>
> Basically, I have a 5 disk RAID-5 array in an Addonics external enclosure.
> Each disk is 1TB in size. Since I am running it over USB, it's takes 3-3.5
> days to resync the disks if something goes pear-shaped.
>
> Now, I don't think the software is at fault because I've had the drive
> replaced with a brand new disk and it's doing the exact same thing -
> drive /dev/sde loses it's partition data (the drive's superblock) and the md
> device's superblock. The data is unaffected since I only ever mount the
> device as read-only unless I need RW capability. I physically power the
> device down after unmounting the partition and stopping the array.
>
> Whilst other people have had this problem of drives suddenly "losing
> everything", they have been able to recover, but I cannot keep my computer
> running for 3-3.5 days just to rebuild good data!
>
> My question is:
>
> Is it possible to copy the md superblock from one known good drive to another
> and assemble it as forced-clean?
>
> It's easy enough to recreate the partition table with a simple:
>
> dd if=/dev/sda of=/dev/sde count=1 bs=512
>
> command but I believe the mdadm superblock lives at the end of the drive and
> if I could recreate that then I could at least recover from a failure of a
> known-good drive without needing a resync.
>
> I'm looking into getting the RAID controller card (actually an eSATA 5-1 mini
> card) replaced or repaired but in the meantime, I am exploring all avenues.
>
> This only happens on /dev/sde and not on any other device. Swapping hard
> drives around doesn't make any difference either - /dev/sde is perfectly
> readable. Clearly, though, I am not happy about building an array with a
> drive in that "cursed" slot since the loss of another drive in a RAID-5 would
> destroy everything stored on the array.
>
> Any advice would be gratefully appreciated.
>
> Regards,
>
> James
>
> PS. I'm running Debian Lenny 2.6.26-2-686 32-bit kernel with mdadm version
> 2.6.7.2-3 (repackaged for Debian).
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>

James,
   Search the LKML for my thread "Drives missing at boot" to see if
you have a problem similar to the one Paul and I have had. If so there
is a kernel patch in the thread which addresses the issue and seems to
work. We both have Asus MBs, new, fast i7 9xx processors, and ran into
this problem.

   In my case drives that were found at boot always continues to work.
The problem I had was they go missing at boot time and then I'd have
to add them back in and do rebuilds, 5 a week at times.

   Anyway, I hope it helps. If not good luck in your search.

Cheers,
Mark
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Re: Missing Drives

[Miles Fidelman]

James Howells wrote:
> Basically, I have a 5 disk RAID-5 array in an Addonics external enclosure.
> Each disk is 1TB in size. Since I am running it over USB, it's takes 3-3.5
> days to resync the disks if something goes pear-shaped.
>
>    
I can't speak to your underlying problem, but if you add an internal (or 
external) bitmap to your array, it speeds up rebuild time considerably.

At create time, you can use the " --bitmap=internal " option.  I know 
you can also add a bitmap to an existing array, but I don't remember the 
magic incantation at the moment (you can probably find it by searching 
the list archives - the topic has come up before).  Or google "write 
intent bitmap."

Miles Fidelman

-- 
In theory, there is no difference between theory and practice.
In<fnord>  practice, there is.   .... Yogi Berra