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SubjectRe: Kernel 2.6.17 and RAID5 Grow Problem (critical section backup)


On Sat, 8 Jul 2006, Neil Brown wrote:

> On Friday July 7, jpiszcz@lucidpixels.com wrote:
>>
>> Hey! You're awake :)
>
> Yes, and thinking about breakfast (it's 8:30am here).
>
>>
>> I am going to try it with just 64kb to prove to myself it works with that,
>> but then I will re-create the raid5 again like I had it before and attempt
>> it again, I did not see that documented anywhere!! Also, how do you use
>> the --backup-file option? Nobody seems to know!
>
> man mdadm
> --backup-file=
> This is needed when --grow is used to increase the number of
> raid-devices in a RAID5 if there are no spare devices avail-
> able. See the section below on RAID_DEVICE CHANGES. The file
> should be stored on a separate device, not on the raid array
> being reshaped.
>
>
> So e.g.
> mdadm --grow /dev/md3 --raid-disk=7 --backup-file=/root/md3-backup
>
> mdadm will copy the first few stripes to /root/md3-backup and start
> the reshape. Once it gets past the critical section, mdadm will
> remove the file.
> If your system crashed during the critical section, then you wont be
> able to assemble the array without providing the backup file:
>
> e.g.
> mdadm --assemble /dev/md3 --backup-file=/root/md3-backup /dev/sd[a-g]
>
> NeilBrown
>

Gotcha, thanks.

Quick question regarding reshaping, must one wait until the re-shape is
completed before he or she grows the file system?

With the re-shape still in progress, I tried to grow the xfs FS but it
stayed the same.

p34:~# df -h | grep /raid5
/dev/md3 746G 80M 746G 1% /raid5

p34:~# mdadm /dev/md3 --grow --raid-disks=4
mdadm: Need to backup 384K of critical section..
mdadm: ... critical section passed.
p34:~#

p34:~# cat /proc/mdstat
md3 : active raid5 hdc1[3] sdc1[2] hde1[1] hda1[0]
781417472 blocks super 0.91 level 5, 64k chunk, algorithm 2 [4/4]
[UUUU]
[>....................] reshape = 0.0% (85120/390708736)
finish=840.5min speed=7738K/sec
p34:~#

p34:~# mount /raid5
p34:~# xfs_growfs /raid5
meta-data=/dev/md3 isize=256 agcount=32, agsize=6104816
blks
= sectsz=4096 attr=0
data = bsize=4096 blocks=195354112, imaxpct=25
= sunit=16 swidth=48 blks, unwritten=1
naming =version 2 bsize=4096
log =internal bsize=4096 blocks=32768, version=2
= sectsz=4096 sunit=1 blks
realtime =none extsz=196608 blocks=0, rtextents=0
data blocks changed from 195354112 to 195354368
p34:~#

p34:~# umount /raid5
p34:~# mount /raid5
p34:~# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/md3 746G 80M 746G 1% /raid5
p34:~#

I guess one has to wait until the reshape is complete before growing the
filesystem..?
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