Re: (help!) MD RAID6 won't --re-add devices?

[Bart Kus <me@bartk.us>]

Things seem to have gone from bad to worse.  I upgraded to the latest 
mdadm, and it actually let me do an --add operation, but --re-add was 
still failing.  It added all the devices as spares though.  I stopped 
the array and tried to re-assemble it, but it's not starting.

jo ~ # mdadm -A /dev/md4 -f -u da14eb85:00658f24:80f7a070:b9026515
mdadm: /dev/md4 assembled from 5 drives and 5 spares - not enough to 
start the array.

How do I promote these "spares" to being the active decides they once 
were?  Yes, they're behind a few events, so there will be some data loss.

--Bart

On 1/13/2011 5:03 AM, Bart Kus wrote:
> Hello,
>
> I had a Port Multiplier failure overnight.  This put 5 out of 10 
> drives offline, degrading my RAID6 array.  The file system is still 
> mounted (and failing to write):
>
> Buffer I/O error on device md4, logical block 3907023608
> Filesystem "md4": xfs_log_force: error 5 returned.
> etc...
>
> The array is in the following state:
>
> /dev/md4:
>         Version : 1.02
>   Creation Time : Sun Aug 10 23:41:49 2008
>      Raid Level : raid6
>      Array Size : 15628094464 (14904.11 GiB 16003.17 GB)
>   Used Dev Size : 1953511808 (1863.01 GiB 2000.40 GB)
>    Raid Devices : 10
>   Total Devices : 11
>     Persistence : Superblock is persistent
>
>     Update Time : Wed Jan 12 05:32:14 2011
>           State : clean, degraded
>  Active Devices : 5
> Working Devices : 5
>  Failed Devices : 6
>   Spare Devices : 0
>
>      Chunk Size : 64K
>
>            Name : 4
>            UUID : da14eb85:00658f24:80f7a070:b9026515
>          Events : 4300692
>
>     Number   Major   Minor   RaidDevice State
>       15       8        1        0      active sync   /dev/sda1
>        1       0        0        1      removed
>       12       8       33        2      active sync   /dev/sdc1
>       16       8       49        3      active sync   /dev/sdd1
>        4       0        0        4      removed
>       20       8      193        5      active sync   /dev/sdm1
>        6       0        0        6      removed
>        7       0        0        7      removed
>        8       0        0        8      removed
>       13       8       17        9      active sync   /dev/sdb1
>
>       10       8       97        -      faulty spare
>       11       8      129        -      faulty spare
>       14       8      113        -      faulty spare
>       17       8       81        -      faulty spare
>       18       8       65        -      faulty spare
>       19       8      145        -      faulty spare
>
> I have replaced the faulty PM and the drives have registered back with 
> the system, under new names:
>
> sd 3:0:0:0: [sdn] Attached SCSI disk
> sd 3:1:0:0: [sdo] Attached SCSI disk
> sd 3:2:0:0: [sdp] Attached SCSI disk
> sd 3:4:0:0: [sdr] Attached SCSI disk
> sd 3:3:0:0: [sdq] Attached SCSI disk
>
> But I can't seem to --re-add them into the array now!
>
> # mdadm /dev/md4 --re-add /dev/sdn1 --re-add /dev/sdo1 --re-add 
> /dev/sdp1 --re-add /dev/sdr1 --re-add /dev/sdq1
> mdadm: add new device failed for /dev/sdn1 as 21: Device or resource busy
>
> I haven't unmounted the file system and/or stopped the /dev/md4 
> device, since I think that would drop any buffers either layer might 
> be holding.  I'd of course prefer to lose as little data as possible.  
> How can I get this array going again?
>
> PS: I think the reason "Failed Devices" shows 6 and not 5 is because I 
> had a single HD failure a couple weeks back.  I replaced the drive and 
> the array re-built A-OK.  I guess it still counted the failure since 
> the array wasn't stopped during the repair.
>
> Thanks for any guidance,
>
> --Bart
>
> PPS: mdadm - v3.0 - 2nd June 2009
> PPS: Linux jo.bartk.us 2.6.35-gentoo-r9 #1 SMP Sat Oct 2 21:22:14 PDT 
> 2010 x86_64 Intel(R) Core(TM)2 Quad CPU @ 2.40GHz GenuineIntel GNU/Linux
> PPS:  # mdadm --examine /dev/sdn1
> /dev/sdn1:
>           Magic : a92b4efc
>         Version : 1.2
>     Feature Map : 0x0
>      Array UUID : da14eb85:00658f24:80f7a070:b9026515
>            Name : 4
>   Creation Time : Sun Aug 10 23:41:49 2008
>      Raid Level : raid6
>    Raid Devices : 10
>
>  Avail Dev Size : 3907023730 (1863.01 GiB 2000.40 GB)
>      Array Size : 31256188928 (14904.11 GiB 16003.17 GB)
>   Used Dev Size : 3907023616 (1863.01 GiB 2000.40 GB)
>     Data Offset : 272 sectors
>    Super Offset : 8 sectors
>           State : clean
>     Device UUID : c0cf419f:4c33dc64:84bc1c1a:7e9778ba
>
>     Update Time : Wed Jan 12 05:39:55 2011
>        Checksum : bdb14e66 - correct
>          Events : 4300672
>
>      Chunk Size : 64K
>
>    Device Role : spare
>    Array State : A.AA.A...A ('A' == active, '.' == missing)
>
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