Re: Backup file size when migrating from raid5 to raid6?

[Thomas Fjellstrom <thomas@fjellstrom.ca>]

On Thu Aug 16, 2012, NeilBrown wrote:
> On Thu, 16 Aug 2012 17:28:13 -0600 Thomas Fjellstrom <thomas@fjellstrom.ca>
> 
> wrote:
> > On Sun May 6, 2012, NeilBrown wrote:
> > > On Mon, 7 May 2012 00:32:35 +0000 Garðar Arnarsson <gardar@giraffi.net>
> > 
> > wrote:
> > > > That's an excellent idea, I was going to add another disk for extra
> > > > space right after migrating to raid6.
> > > > 
> > > > Just to be clear, I'll be running the normalize attribute just once
> > > > to straighten the array out right? Or will I have to do it for every
> > > > extra drive I add in the future?
> > > 
> > > Just once.
> > > 
> > > > And what are the N+1 you mention in --raid-devices=N+1
> > > 
> > > By "N+1" I just meant "1 more than the number of devices currently in
> > > the array".
> > > 
> > > If you have both new devices ready to go, you just do a single reshape
> > > operation that converts to RAID6 and adds more space.  This does not
> > > need a backup file and is probably the best approach.
> > > 
> > > If you currently have a 10-drive RAID5 and want a 12-drive RAID6, then
> > > 
> > >  mdadm --grow /dev/md0 --raid-devices=12 --level=6
> > > 
> > > is what you want.
> > 
> > I apologize for bringing back a long dead thread, but I've been wondering
> > if mdadm does the grow op in this case, in one step? Or does it
> > internally do each step separately, doing a reshape with each one?
> > 
> > I've currently got a 7x1TB disk raid5, and have a couple more disks to
> > add and I was planning on moving to raid6. I'm hoping to reduce the
> > amount of time the array is "reshaping" because I'm a bit paranoid that
> > my bad luck with hard drives will decide to hit right then and there.
> 
> If you change the level and the number of devices in the one command, and
> there are already enough spares present to satisfy the requirements of the
> new size, then it will only perform a single reshape operation which will
> use the minimal amount of time.

Ah. Thank you for clarifying that for me :) just running the two new drives 
through a bit of a stress test. Then I'll get to expanding the array.

Thanks.

> NeilBrown


-- 
Thomas Fjellstrom
thomas@fjellstrom.ca
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