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

[Justin Piszcz <jpiszcz@lucidpixels.com>]

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..?