[CentOS] help with rebuilding md0 (Raid5)
Scott Silva
ssilva at sgvwater.com
Wed May 20 16:23:21 UTC 2009
on 5-20-2009 8:32 AM Daniel Bird spake the following:
> Sorry, this is going to be a rather long post...Here's the situation; I
> have 4 IDE disks from an old snap server which fails to mount the raid
> array. We believe there is a controller error on the SNAP so we've put
> them in another box running CentOS 5 and can see the disks OK.
>
> hda thru hdd looks like this
>
> Disk /dev/hdd: 185.2 GB, 185283624960 bytes
> 255 heads, 63 sectors/track, 22526 cylinders
> Units = cylinders of 16065 * 512 = 8225280 bytes
>
> Device Boot Start End Blocks Id System
> /dev/hdd1 * 1 2 16041+ 83 Linux
> /dev/hdd2 3 70 546210 83 Linux
> /dev/hdd3 71 138 546210 5 Extended
> /dev/hdd4 139 21781 173844468 83 Linux
> /dev/hdd5 71 104 273104+ 83 Linux
> /dev/hdd6 105 138 273104+ 83 Linux
>
>
> I can mount hdX1 and hdX2 (hdx2 is xfs) on all disks.
>
> Now /etc/raidtab (from one of the hdx2 partions) has the following entry
> which I'd like to re-create on the CentOS box
>
> raiddev /dev/md0
> raid-level 5
> nr-raid-disks 4
> nr-spare-disks 0
> persistent-superblock 1
> chunk-size 64
> device /dev/hda4
> raid-disk 0
> device /dev/hdc4
> raid-disk 1
> device /dev/hde4
> raid-disk 2
> device /dev/hdg4
> raid-disk 3
>
> I've also checked the superblocks
>
> /dev/hda4:
> Magic : a92b4efc
> Version : 00.90.00
> UUID : a72e334f:a9ccba81:bba665d8:82a3c378
> Creation Time : Mon Jun 30 12:00:28 2003
> Raid Level : raid5
> Used Dev Size : 173844352 (165.79 GiB 178.02 GB)
> Array Size : 521533056 (497.37 GiB 534.05 GB)
> Raid Devices : 4
> Total Devices : 3
> Preferred Minor : 0
>
> Update Time : Tue May 19 21:40:43 2009
> State : active
> Active Devices : 2
> Working Devices : 2
> Failed Devices : 1
> Spare Devices : 0
> Checksum : cbe14089 - correct
> Events : 0.22
>
> Layout : left-asymmetric
> Chunk Size : 64K
>
> Number Major Minor RaidDevice State
> this 0 3 4 0 active sync /dev/hda4
>
> 0 0 3 4 0 active sync /dev/hda4
> 1 1 22 4 1 faulty /dev/hdc4
> 2 2 0 0 2 faulty removed
> 3 3 34 4 3 active sync
> /dev/hdb4:
> Magic : a92b4efc
> Version : 00.90.00
> UUID : a72e334f:a9ccba81:bba665d8:82a3c378
> Creation Time : Mon Jun 30 12:00:28 2003
> Raid Level : raid5
> Used Dev Size : 173844352 (165.79 GiB 178.02 GB)
> Array Size : 521533056 (497.37 GiB 534.05 GB)
> Raid Devices : 4
> Total Devices : 3
> Preferred Minor : 0
>
> Update Time : Sat Aug 2 19:26:28 2008
> State : active
> Active Devices : 3
> Working Devices : 3
> Failed Devices : 0
> Spare Devices : 0
> Checksum : ca62ce2c - correct
> Events : 0.21
>
> Layout : left-asymmetric
> Chunk Size : 64K
>
> Number Major Minor RaidDevice State
> this 1 22 4 1 active sync /dev/hdc4
>
> 0 0 3 4 0 active sync /dev/hda4
> 1 1 22 4 1 active sync /dev/hdc4
> 2 2 0 0 2 faulty removed
> 3 3 34 4 3 active sync
> /dev/hdc4:
> Magic : a92b4efc
> Version : 00.90.00
> UUID : a72e334f:a9ccba81:bba665d8:82a3c378
> Creation Time : Mon Jun 30 12:00:28 2003
> Raid Level : raid5
> Used Dev Size : 173844352 (165.79 GiB 178.02 GB)
> Array Size : 521533056 (497.37 GiB 534.05 GB)
> Raid Devices : 4
> Total Devices : 4
> Preferred Minor : 0
>
> Update Time : Sun Jul 22 22:33:00 2007
> State : active
> Active Devices : 4
> Working Devices : 4
> Failed Devices : 0
> Spare Devices : 0
> Checksum : c871f493 - correct
> Events : 0.18
>
> Layout : left-asymmetric
> Chunk Size : 64K
>
> Number Major Minor RaidDevice State
> this 2 33 4 2 active sync
>
> 0 0 3 4 0 active sync /dev/hda4
> 1 1 22 4 1 active sync /dev/hdc4
> 2 2 33 4 2 active sync
> 3 3 34 4 3 active sync
> /dev/hdd4:
> Magic : a92b4efc
> Version : 00.90.00
> UUID : a72e334f:a9ccba81:bba665d8:82a3c378
> Creation Time : Mon Jun 30 12:00:28 2003
> Raid Level : raid5
> Used Dev Size : 173844352 (165.79 GiB 178.02 GB)
> Array Size : 521533056 (497.37 GiB 534.05 GB)
> Raid Devices : 4
> Total Devices : 3
> Preferred Minor : 0
>
> Update Time : Sat Aug 2 19:26:28 2008
> State : active
> Active Devices : 3
> Working Devices : 3
> Failed Devices : 0
> Spare Devices : 0
> Checksum : ca62ce3c - correct
> Events : 0.21
>
> Layout : left-asymmetric
> Chunk Size : 64K
>
> Number Major Minor RaidDevice State
> this 3 34 4 3 active sync
>
> 0 0 3 4 0 active sync /dev/hda4
> 1 1 22 4 1 active sync /dev/hdc4
> 2 2 0 0 2 faulty removed
> 3 3 34 4 3 active sync
>
>
>
> This is my fist stab and re-assembling an array after moving the disks
> so I though I'd double check how I would go about re-assembling this Can
> I simply do
>
> mdadm --assemble --scan
>
> ? Or do I need to reset the superblocks and re-assemble in degraded mode
> somehow?
>
> TIA
>
> Dan
Are you sure that all the disks are in the same position that they were in
when removed from the snap server? IE... hda on the snap is still hda on the
new controller. If so, you could try the assemble command. Otherwise you will
have to do some creative work to get it going. But from the above superblocks,
the array is very dirty, and some drives have different array status, so you
might have to force things along. If this data is critical, I would dd the
drives onto other hardware and experiment there, or at least dd the drives to
image files and try those. If you succeed, you can backup the data and restore
later. If you fail with the original drives, you might render the array
unrecoverable.
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