On Wed, Oct 13, 2010 at 11:08:23AM +1100, Neil Brown wrote:
> On Wed, 13 Oct 2010 00:59:52 +0200
> Simon SÉHIER <simon@xxxxxxxxx> wrote:
>
> > On 12 oct. 2010 22:46:12, Neil Brown wrote :
> > > On Tue, 12 Oct 2010 16:27:53 +0200
> > >
> > > Simon S <simon@xxxxxxxxx> wrote:
> > > > Hi all,
> > > >
> > > > I had a config with 5 disks and 3 raid 5 arrays:
> > > >
> > > > md2 : system root
> > > > md3 : swap
> > > > md4 : data
> > > >
> > > > I added a 6th disk with the intention of growing my raid5 into raid6.
> > > >
> > > > The step I used were :
> > > >
> > > > # mdadm /dev/mdX -a /dev/newdiskX
> > > > # mdadm -G --level 6 -n 6 /dev/mdX --backup-file /mdXbackup
> > > >
> > > > (yes, with backup file on root partition md2...)
> > >
> > > Bad idea.. Very bad idea.
> > >
> > > > The md3 array reshaped without any problem.
> > > > md2 seemed to reshape well until it reaches 50.4%, then the rebuild speed
> > > > stalled at 14Kb/s.
> > >
> > > This is the expected consequence of that bad idea. Unfortunately it would
> > > be hard to reliably get mdadm to complain about that, though I guess the
> > > common cases are easy to protect against ... added to 'todo' list
> > >
> > > > md4 was still in the state "resync=DELAYED" then.
> > > >
> > > > As the rebuild process seemed hung, I restart the machine ... bad idea.
> > >
> > > Not really, nothing else would have worked.
> > >
> > > > Now mdadm refuses to assemble md2 and md4, and displays this message :
> > > > mdadm: Failed to restore critical section for reshape, sorry.
> > > >
> > > > Possibly you needed to specify the --backup-file
> > > >
> > > > md2 is my linux installation, not very bad if I lose this one.
> > > >
> > > > md4 however contains valuable data.
> > > >
> > > > While md4 was still in the state resync=DELAYED before the shutdown, I
> > > > expect it should not has been (to much) modified and can be recovered.
> > >
> > > Very true.
> > >
> > > > Any idea on how I could safely do it ?
> > > >
> > > > Should I give a try to the hack "Get 'Grow_restart' to always return 0."
> > > > mentionned by Neil Brown on 22 april 2010 in this mailing list ?
> > >
> > > That is your best bet. I plan to make that easier to do in mdadm-3.2 (no
> > > recompile necessary).
> > >
> > > Before you do, check "mdadm -E /dev/newdiskX" and make sure the "Reshape
> > > position" is 0. If it is you should be fine. I
> > >
> > > It won't be for md2 of course. So md will quite possible have some
> > > corruption. Run fsck on it an it will probably be mostly OK, but there is
> > > a reasonable chance that some files will be corrupted. Whether and when
> > > you will notice is impossible to guess.
> >
> > Thanks for your answer Neil,
> >
> > I recompiled mdadm 3.1.4 with return 0 in the beginning of the function
> > Grow_restart (mistake was made with 3.1.2). I have one more question :
> >
> > I first tried assembling the least valued array, md2. It starts reshaping from
> > where it stops, in the first seconds around 1300 K/s, and rapidly above 10K/s.
> >
> > While my backup file for md4 (the array I care about) was also on md2. Do I
> > have to expect a problem assembling md4 with the modified version of mdadm, or
> > can I go without worying md2 (rootfs) isn't assembled ?
>
> The backup file for md4 would have been essentially empty. It can be created
> anew elsewhere. I probably wouldn't rick using the original backup file
> even if you can access it, as it could be corrupted.
> So when you assemble md4, give it a fresh backup file in some stable location,
> and use the hacked mdadm.
>
> NeilBrown
>
I tried
# mdadm -A --backup-file=/new-empty-md4backup-file /dev/md4
but the array is now in "inactive" state with 6 spares :
md4 : inactive sdc4[0](S) sdh4[6](S) sdg4[5](S) sdf4[3](S) sde4[2](S) sdd4[1](S)
1411288041 blocks super 1.2
I'm a bit confuse on what I could do now.
# mdadm -E /dev/sd?4 | grep 'Role\|Stat\|pos\|dev.sd\|Lev\|Time\|Even'
/dev/sdc4:
Raid Level : raid6
State : active
Reshape pos'n : 0
Events : 97
Device Role : Active device 0
Array State : AAAAA. ('A' == active, '.' == missing)
/dev/sdd4:
Raid Level : raid6
State : active
Reshape pos'n : 0
Events : 97
Device Role : Active device 1
Array State : AAAAA. ('A' == active, '.' == missing)
/dev/sde4:
Raid Level : raid6
State : active
Reshape pos'n : 0
Events : 97
Device Role : Active device 2
Array State : AAAAA. ('A' == active, '.' == missing)
/dev/sdf4:
Raid Level : raid6
State : active
Reshape pos'n : 0
Events : 97
Device Role : Active device 3
Array State : AAAAA. ('A' == active, '.' == missing)
/dev/sdg4:
Raid Level : raid6
State : active
Reshape pos'n : 0
Events : 97
Device Role : Active device 4
Array State : AAAAA. ('A' == active, '.' == missing)
/dev/sdh4:
Raid Level : raid6
State : active
Reshape pos'n : 0
Events : 97
Device Role : spare
Array State : AAAAA. ('A' == active, '.' == missing)
--
Simon
> >
> >
> > >
> > > NeilBrown
> > >
> > > > Thank for any advices,
> > > >
> > > > Cheers,
> > >
> > > --
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