On Sun, 25 Sep 2011 21:23:31 -0700 "Kenn" <kenn@kenn.us> wrote:

> I have a raid5 array that had a drive drop out, and resilvered the wrong
> drive when I put it back in, corrupting and destroying the raid.  I
> stopped the array at less than 1% resilvering and I'm in the process of
> making a dd-copy of the drive to recover the files.

I don't know what you mean by "resilvered".

> 
> (1) Is there anything diagnostic I can contribute to add more
> wrong-drive-resilvering protection to mdadm?  I have the command history
> showing everything I did, I have the five drives available for reading
> sectors, I haven't touched anything yet.

Yes, report the command history, and any relevant kernel logs, and the output
of "mdadm --examine" on all relevant devices.

NeilBrown


> 
> (2) Can I suggest improvements into resilvering?  Can I contribute code to
> implement them?  Such as resilver from the end of the drive back to the
> front, so if you notice the wrong drive resilvering, you can stop and not
> lose the MBR and the directory format structure that's stored in the first
> few sectors?  I'd also like to take a look at adding a raid mode where
> there's checksum in every stripe block so the system can detect corrupted
> disks and not resilver.  I'd also like to add a raid option where a
> resilvering need will be reported by email and needs to be started
> manually.  All to prevent what happened to me from happening again.
> 
> Thanks for your time.
> 
> Kenn Frank
> 
> P.S.  Setup:
> 
> # uname -a
> Linux teresa 2.6.26-2-686 #1 SMP Sat Jun 11 14:54:10 UTC 2011 i686 GNU/Linux
> 
> # mdadm --version
> mdadm - v2.6.7.2 - 14th November 2008
> 
> # mdadm --detail /dev/md3
> /dev/md3:
>         Version : 00.90
>   Creation Time : Thu Sep 22 16:23:50 2011
>      Raid Level : raid5
>      Array Size : 2930287616 (2794.54 GiB 3000.61 GB)
>   Used Dev Size : 732571904 (698.64 GiB 750.15 GB)
>    Raid Devices : 5
>   Total Devices : 4
> Preferred Minor : 3
>     Persistence : Superblock is persistent
> 
>     Update Time : Thu Sep 22 20:19:09 2011
>           State : clean, degraded
>  Active Devices : 4
> Working Devices : 4
>  Failed Devices : 0
>   Spare Devices : 0
> 
>          Layout : left-symmetric
>      Chunk Size : 64K
> 
>            UUID : ed1e6357:74e32684:47f7b12e:9c2b2218 (local to host teresa)
>          Events : 0.6
> 
>     Number   Major   Minor   RaidDevice State
>        0      33        1        0      active sync   /dev/hde1
>        1      56        1        1      active sync   /dev/hdi1
>        2       0        0        2      removed
>        3      57        1        3      active sync   /dev/hdk1
>        4      34        1        4      active sync   /dev/hdg1
> 
>