Re: Converting from Raid 5 to 6

[NeilBrown <neilb@suse.de>]

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On Sat, 30 Nov 2013 22:13:58 +0000 Michael Busby <michael.a.busby@gmail.com>
wrote:

> Sorry to bring up a old thread, last night i had a power cut and this
> morning when the power has come back i have tried to boot the server,
> but the raid will not assemble on using a live CD i have found that
> one of the disk is reporting "possibly out of date" is there any way
> to force this disk back in? the bigger problem i have is that my
> external caddie has died so i was running a degraded raid 6 but now it
> is only starting with 4 out of 6 devices. is there anyway to get this
> back?

It's really hard to know what is possible without precise details.
Output of "mdadm -E" for each member device is always a good idea.
If you are having trouble assembling, then output of the assemble command
with -vv added never goes astray.
Have you tried adding "-f" to the assemble command.  Often helps and is
unlikely to hurt.

> 
> i have though about recreating the array using the --assume-clean
> option but not sure if that's a good idea

Not a good idea except as a very last resort.

NeilBrown


> 
> any help will be much appreciated
> 
> 
> 
> On 24 October 2011 21:47, Michael Busby <michael.a.busby@gmail.com> wrote:
> >
> > I was sure i added the device before, but when rebooted the system it
> > has seemed to lose the extra drive and i had already restarted the
> > grow command with out checking the disk was there, so more than likely
> > a mistake by me
> >
> >
> >
> > On 24 October 2011 21:39, NeilBrown <neilb@suse.de> wrote:
> > > On Mon, 24 Oct 2011 21:19:22 +0100 Michael Busby <michael.a.busby@gmail.com>
> > > wrote:
> > >
> > >> Ok thanks, i have 1 small issue, when added the extra disk its been
> > >> maked as spare, is this normal?
> > >>
> > >> Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5]
> > >> [raid4] [raid10]
> > >> md0 : active raid6 sde[0] sdg[6](S) sda[4] sdb[3] sdd[2] sdc[1]
> > >>       7814055936 blocks super 1.0 level 6, 512k chunk, algorithm 18
> > >> [6/5] [UUUUU_]
> > >>       [>....................]  reshape =  3.0% (59244544/1953513984)
> > >> finish=11122.8min speed=2837K/sec
> > >>
> > >
> > > It looks like the extra drive was added after you started the grow.
> > >
> > > So it is still a spare.
> > > Once the grow finishes you will have a singly-degraded RAID6.
> > > Then it will immediately start recovering the missing device to the spare.
> > >
> > > Did you add the extra drive after starting the grow - or before??
> > >
> > > NeilBrown
> > >
> > >
> >
> >
> > >
> > >>
> > >>
> > >>
> > >> On 24 October 2011 21:14, NeilBrown <neilb@suse.de> wrote:
> > >> > On Mon, 24 Oct 2011 17:03:46 +0100 Michael Busby <michael.a.busby@gmail.com>
> > >> > wrote:
> > >> >
> > >> >> should the speed be very slow when doing this progress, its a lot
> > >> >> slower than a normal grow
> > >> >
> > >> > Yes.
> > >> > The array is being reshaped in-place.  i.e. data is being read from part of
> > >> > the array, rearranged, and written back to the same part of the array.
> > >> > As you can imagine, this is risky - a crash will leave an inconsistent state.
> > >> > Hence the backup file.  Everything in the array is first written to the
> > >> > backup file, then back to the array.  So it is slow.
> > >> >
> > >> > A "normal" grow is writing to somewhere where there is no valid data, so it
> > >> > doesn't need the backup.
> > >> >
> > >> > I do have a plan to make this faster.... but I have lots of plans and little
> > >> > time.
> > >> >
> > >> > NeilBrown
> > >> >
> > >> >
> > >> >
> > >> >
> > >> >>
> > >> >> reshape =  1.2% (25006080/1953513984) finish=12481.8min speed=2574K/sec
> > >> >>
> > >> >> On 24 October 2011 15:11, Mathias Burén <mathias.buren@gmail.com> wrote:
> > >> >> > On 24 October 2011 14:11, Michael Busby <michael.a.busby@gmail.com> wrote:
> > >> >> >> At the moment i have a raid5 setup with 5 disks, i am looking to add a
> > >> >> >> 6th disk and change from raid 5 to raid 6
> > >> >> >>
> > >> >> >> having looked at Neil's site i have found the following command, and
> > >> >> >> just want to double check this is still the recommend way of
> > >> >> >> converting
> > >> >> >>
> > >> >> >> mdadm --grow /dev/md0 --level=6 --raid-disks=6 --backup-file=/home/md.backup
> > >> >> >>
> > >> >> >> also would i need to add the extra disk before or after the command?
> > >> >> >>
> > >> >> >> cheers
> > >> >> >> --
> > >> >> >> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> > >> >> >> the body of a message to majordomo@vger.kernel.org
> > >> >> >> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > >> >> >>
> > >> >> >
> > >> >> > Hi,
> > >> >> >
> > >> >> > I grew my 6 disk RAID5 to a 7 disk RAID6. First, add the drive. Then
> > >> >> > partition it as required. Then add the drive to the array (I think
> > >> >> > it'll become a spare?). Then you can grow it.
> > >> >> >
> > >> >> > Make sure you're using the latest mdadm tools available.
> > >> >> >
> > >> >> > Regards,
> > >> >> > Mathias
> > >> >> >
> > >> >> --
> > >> >> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> > >> >> the body of a message to majordomo@vger.kernel.org
> > >> >> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > >> >
> > >> >
> > >
> > >


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