From: NeilBrown <neilb@suse.de>
To: "Garðar Arnarsson" <gardar@giraffi.net>
Cc: linux-raid@vger.kernel.org
Subject: Re: Backup file size when migrating from raid5 to raid6?
Date: Sun, 6 May 2012 21:00:28 +1000 [thread overview]
Message-ID: <20120506210028.6212b2f8@notabene.brown> (raw)
In-Reply-To: <CAH-e9vLiK6=HmDjM=Ub7p_Lxrp_L0x1bkAa2oP=ykajqvtkfDQ@mail.gmail.com>
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On Sun, 6 May 2012 10:17:52 +0000 Garðar Arnarsson <gardar@giraffi.net> wrote:
> My raid5 array has gotten a bit big, it's containing total 10 drives
> right now (I started out with 3 drives). So I am going to convert it
> to raid6 before it gets any bigger.
>
> I am doing a test-run on a virtual machine with virtual drives to see
> that everything works flawlessly.
>
> When I tried to convert the array to raid6 I got a error message about
> a missing backup-file
>
> mdadm --grow /dev/md0 --raid-devices=5 --level=6
>
> mdadm level of /dev/md0 changed to raid6
> mdadm: /dev/md0: Cannot grow - need backup-file
> mdadm: aborting level change
>
> I added the backup file and was able to convert the array successfully
> after that.
>
> My question is, how big is this backup file going to be? My real raid
> array consists of 2tb drives, will the backup file be as big as one
> drive in the array, or will it just be few megabytes or gigabytes?
> I'm asking because I'm wondering if I need to buy an extra hdd for the
> backup file or if the backup file can just be on my OS hdd that has
> around 100gb free.
The backup file is a few megabytes. Around 16MB I think.
However if you are likely to add another device in the not too distant future
you can save yourself a bit of time.
If you
mdadm --grow /dev/md0 --level=6 --layout=preserve
It will just make the new few a 'Q-block' device, containing the extra RAID6
'parity' block for each stripe. This doesn't require any reshape or or any
backup file and is a lot faster. All it requires is a normal recovery
operation.
Then when you later add another device you can
mdadm --grow /dev/md0 --raid-devices=N+1 --layout=normalise
This will convert from the Q-on-the-last-device layout to a more normal
rotated-P-and-Q layout at the same time as adding extra space.
NeilBrown
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next prev parent reply other threads:[~2012-05-06 11:00 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAH-e9vLTY2eo0p3ud5FaWNe_2f8hej0aitFuu8K0M1RZdObiXQ@mail.gmail.com>
2012-05-06 10:17 ` Backup file size when migrating from raid5 to raid6? Garðar Arnarsson
2012-05-06 11:00 ` NeilBrown [this message]
[not found] ` <CAH-e9vJkrv2R-HTR7JfHwZK1sbYQ3fduGbtxEwtor4gtyd6PKQ@mail.gmail.com>
2012-05-07 0:35 ` Garðar Arnarsson
2012-05-07 0:54 ` NeilBrown
2012-08-16 23:28 ` Thomas Fjellstrom
2012-08-17 0:39 ` NeilBrown
2012-08-17 0:45 ` Thomas Fjellstrom
2012-08-17 0:52 ` John Robinson
2013-07-17 13:01 ` Boyan Alexiev
2013-07-17 20:51 ` NeilBrown
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