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From: Wols Lists <antlists@youngman.org.uk>
To: Nix <nix@esperi.org.uk>, NeilBrown <neilb@suse.com>
Cc: linux-raid@vger.kernel.org
Subject: Re: 4.11.2: reshape raid5 -> raid6 atop bcache deadlocks at start on md_attr_store / raid5_make_request
Date: Mon, 22 May 2017 20:07:18 +0100	[thread overview]
Message-ID: <592336E6.8080906@youngman.org.uk> (raw)
In-Reply-To: <87o9ukykmk.fsf@esperi.org.uk>

On 22/05/17 16:30, Nix wrote:
> I'll give it a try -- I hit it twice in succession, once with a
> --backup-file, once without. Since mdadm does not warn about the lack of
> a --backup-file, I guess the statement in the manual that it is
> essential to provide one when changing RAID levels is untrue: I suspect
> that it's necessary *if* you're not increasing the number of disks at
> the same time, but since I'm growing into a spare, adding a
> --backup-file only slows it down?

I did discuss this with Neil while I wrote it, so I hope I got it right :-)

https://raid.wiki.kernel.org/index.php/A_guide_to_mdadm#Array_internals_and_how_it_affects_mdadm

aiui, provided you're using a v1 superblock, the data offset means there
is spare space on the drives precisely for the purpose (one of then at
least) of keeping a backup. So the reshape will start reshaping into the
spare space and eliminate the need for the backup - the new version of
the stripe will be safely written before the space occupied by the old
stripe is required.

Cheers,
Wol

  reply	other threads:[~2017-05-22 19:07 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-05-22  9:13 4.11.2: reshape raid5 -> raid6 atop bcache deadlocks at start on md_attr_store / raid5_make_request Nix
2017-05-22 11:35 ` NeilBrown
2017-05-22 15:30   ` Nix
2017-05-22 19:07     ` Wols Lists [this message]
2017-05-22 20:43       ` Nix
2017-05-23  1:20         ` NeilBrown
2017-05-23 10:10           ` Nix
2017-05-23  1:39       ` NeilBrown
2017-05-23 14:47         ` Wols Lists
2017-05-24  1:50           ` NeilBrown
2017-05-23  1:07     ` NeilBrown
2017-05-22 21:38   ` Nix
2017-05-23 14:16     ` Wols Lists
2017-05-23 15:00       ` Nix
2017-05-24  1:24     ` NeilBrown
2017-05-24 13:28       ` Nix
2017-05-25  1:31         ` NeilBrown
2017-05-25 12:14           ` Nix
2017-05-24 19:42       ` Nix
2017-05-24 22:57       ` Shaohua Li
2017-05-25  1:30         ` NeilBrown
2017-05-25  1:46           ` Shaohua Li
2017-05-26  3:23             ` NeilBrown
2017-05-26 16:40               ` Shaohua Li
2017-05-28 23:17         ` NeilBrown
2017-05-30 17:41           ` Shaohua Li
2017-06-05  6:49             ` [PATCH] md: fix deadlock between mddev_suspend() and md_write_start() NeilBrown
2017-06-06  0:01               ` Shaohua Li
2017-06-07  1:45                 ` NeilBrown

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