Re: reshape raid5 to raid6

[Michael Ole Olsen <gnu@gmx.net>]

Is there any way to get anything below 2.6.30 to recognize this
'fake' raid6 with all Q blocks on the last disk?

I reshaped my raid5 to raid6 using this echo into /sys

The 2.6.30 and 2.6.30.1 is terribly unstable with xfs+nfs 
(1-3 kernel oopses a day and complete resync much of the time) 
(I have sent a bug report to xfs mailing list, it seems to be xfs/nfs)

Best regards,
Michael Ole Olsen

Neil Brown schrieb am Friday, den 26. June 2009:

> On Wednesday June 24, billycrook@gmail.com wrote:
> > On Wed, Jun 24, 2009 at 06:20, NeilBrown<neilb@suse.de> wrote:
> > > On Wed, June 24, 2009 8:27 pm, Michael Ole Olsen wrote:
> > >> Is it possible to reshape my /dev/md0 raid5 into raid6?
> > >
> > > If you are are using Linux 2.6.30, then you can
> > >
> > >  echo raid6 > /sys/block/md0/md/level
> > >
> > > and it will instantly be sort-of-raid6.
> > > It is exactly like raid6 except that the Q blocks are all one
> > > the one drive, and drive that previously didn't exist.
> > > If you have a spare, it will start building the Q blocks
> > > on that drive and when it finishes you will have true raid6
> > > redundancy, though possibly a little less than raid6 performance,
> > > as a real raid6 has the Q block distributed.
> > >
> > > When mdadm-3.1 is released, you will be able to tell the raid6
> > > to re-stripe with a more traditional layout.  This will take quite
> > > a while, but you can continue to use the array (though a bit more
> > > slowly) will it progresses.
> > > Of course you don't need to do that step if you don't want to.
> > 
> > I have a raid5 array on 2.6.18 that I'd like to grow like this.  I
> > might wait until mdadm-3.1 so I can stripe Q from the git-go.  I'd
> > like to --stop the array on the 2.6.18 machine, and export the
> > individual disks over iscsi to a 2.6.30 machine, and use the newer
> > mdadm there to grow the array from raid5 to raid6.  Then --stop it on
> > the 2.6.30 machine, unexport the disks, and --start the array again on
> > the 2.6.18 machine.  Disclaimers aside, should that work?  My main
> > concern is 2.6.18's ability to work with this 'creative' raid6
> > implementation that currently results from the grow from raid5 to
> > raid6.
> 
> 2.6.18 will not understand the raid6 created by simply echoing 'raid6'
> in to the 'level' file.  It will need to be restriped with the help of
> mdadm-3.1 first.
> 
> > 
> > I've also got a few disks to add, so maybe the better solution would
> > be to add one and get the unstriped Q, then add another and let Q
> > stripe with everything else during the reshape.  That is, if it will
> > stripe Q during the reshape.
> 
> Your best bet would be to wait for mdadm-3.1 and do it all at once,
> something like:
>   mdadm --grow /dev/md0 --level=raid6 --raid-disks=8
> 
> NeilBrown
> --
> 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
--
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