I have a Raid5 array with 4 devices that I wanted to see if I could get
a better performance out of, so i tried changing the chunk size from 64K
to something bigger. (famous last words) . I got into some other
trouble and thought I needed a reboot. On reboot I several times managed
to mount and specify the device with my backup file during initramfs,
but the reshape stopped every time once the system was at initialized.
This is under debian sqeeze with a 3.2.0-0.bpo.3-686-pae kernel from
backports. I installed mdadm from backports to get the latest version of
that as well, and tried rebooting with --freeze-reshape. Suspect that I
mixed up my initrd.img-files and started without --freeze-reshape the
first time after installing the new mdadm. Now mdadm says it can not
find a backup in my backup file. Opening up the backup in emacs, it
seems to contain only NULs. Can't be right, can it? I have been mounting
the backup under a directory under /dev/, on the assumption that the
mount wold survive past the initramfs stage.
My bumbling has been happening with a current, correct,
/etc/mdadm/mdadm.conf containigng:
--------
DEVICE /dev/sdh /dev/sde /dev/sdc /dev/sdd
CREATE owner=root group=disk mode=0660 auto=yes
HOMEHOST <system>
ARRAY /dev/md1 level=raid5 num-devices=4
UUID=583001c4:650dcf0c:404aaa6f:7fc38959 spare-group=main
-------
The show-stopper happened with an initramfs and a script in
/scripts/local-top/mdadm along the lines of:
-------
/sbin/mdadm --assemble -f --backup-file=/dev/bak/md1-backup /dev/md1
--run --auto=yes /dev/sdh /dev/sde /dev/sdc /dev/sdd
-------
At times I have also had to use the env-variable MDADM_GROW_ALLOW_OLD=1
Below is the output of mdadm -Evvvvs:
--------
/dev/sdh:
Magic : a92b4efc
Version : 0.91.00
UUID : 583001c4:650dcf0c:404aaa6f:7fc38959
Creation Time : Wed Dec 3 19:45:33 2008
Raid Level : raid5
Used Dev Size : 976762496 (931.51 GiB 1000.20 GB)
Array Size : 2930287488 (2794.54 GiB 3000.61 GB)
Raid Devices : 4
Total Devices : 4
Preferred Minor : 1
Reshape pos'n : 2368561152 (2258.84 GiB 2425.41 GB)
New Chunksize : 131072
Update Time : Wed Oct 17 02:15:53 2012
State : active
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Checksum : 14da0760 - correct
Events : 778795
Layout : left-symmetric
Chunk Size : 64K
Number Major Minor RaidDevice State
this 0 8 112 0 active sync /dev/sdh
0 0 8 112 0 active sync /dev/sdh
1 1 8 48 1 active sync /dev/sdd
2 2 8 32 2 active sync /dev/sdc
3 3 8 64 3 active sync /dev/sde
/dev/sde:
Magic : a92b4efc
Version : 0.91.00
UUID : 583001c4:650dcf0c:404aaa6f:7fc38959
Creation Time : Wed Dec 3 19:45:33 2008
Raid Level : raid5
Used Dev Size : 976762496 (931.51 GiB 1000.20 GB)
Array Size : 2930287488 (2794.54 GiB 3000.61 GB)
Raid Devices : 4
Total Devices : 4
Preferred Minor : 1
Reshape pos'n : 2368561152 (2258.84 GiB 2425.41 GB)
New Chunksize : 131072
Update Time : Wed Oct 17 02:15:53 2012
State : active
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Checksum : 14da0736 - correct
Events : 778795
Layout : left-symmetric
Chunk Size : 64K
Number Major Minor RaidDevice State
this 3 8 64 3 active sync /dev/sde
0 0 8 112 0 active sync /dev/sdh
1 1 8 48 1 active sync /dev/sdd
2 2 8 32 2 active sync /dev/sdc
3 3 8 64 3 active sync /dev/sde
/dev/sdc:
Magic : a92b4efc
Version : 0.91.00
UUID : 583001c4:650dcf0c:404aaa6f:7fc38959
Creation Time : Wed Dec 3 19:45:33 2008
Raid Level : raid5
Used Dev Size : 976762496 (931.51 GiB 1000.20 GB)
Array Size : 2930287488 (2794.54 GiB 3000.61 GB)
Raid Devices : 4
Total Devices : 4
Preferred Minor : 1
Reshape pos'n : 2368561152 (2258.84 GiB 2425.41 GB)
New Chunksize : 131072
Update Time : Wed Oct 17 02:15:53 2012
State : active
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Checksum : 14da0714 - correct
Events : 778795
Layout : left-symmetric
Chunk Size : 64K
Number Major Minor RaidDevice State
this 2 8 32 2 active sync /dev/sdc
0 0 8 112 0 active sync /dev/sdh
1 1 8 48 1 active sync /dev/sdd
2 2 8 32 2 active sync /dev/sdc
3 3 8 64 3 active sync /dev/sde
/dev/sdd:
Magic : a92b4efc
Version : 0.91.00
UUID : 583001c4:650dcf0c:404aaa6f:7fc38959
Creation Time : Wed Dec 3 19:45:33 2008
Raid Level : raid5
Used Dev Size : 976762496 (931.51 GiB 1000.20 GB)
Array Size : 2930287488 (2794.54 GiB 3000.61 GB)
Raid Devices : 4
Total Devices : 4
Preferred Minor : 1
Reshape pos'n : 2368561152 (2258.84 GiB 2425.41 GB)
New Chunksize : 131072
Update Time : Wed Oct 17 02:15:53 2012
State : active
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Checksum : 14da0722 - correct
Events : 778795
Layout : left-symmetric
Chunk Size : 64K
Number Major Minor RaidDevice State
this 1 8 48 1 active sync /dev/sdd
0 0 8 112 0 active sync /dev/sdh
1 1 8 48 1 active sync /dev/sdd
2 2 8 32 2 active sync /dev/sdc
3 3 8 64 3 active sync /dev/sde
---------------------------
I guess the moral of all this is that if you want to use mdadm you
should pay attention and not be in too much of a hurry :-/ .
I'm just hoping that I can get my system back. This raid contains my
entire system, and will take a LOT of work to recreate. Mail, calendars
... . Backups are a couple of weeks old ...
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