From: Wols Lists <antlists@youngman.org.uk>
To: Amy Chiang <amychiang@qnap.com>, linux-raid@vger.kernel.org
Subject: Re: conf->min_offset_diff calculation timing of growing raid5
Date: Tue, 2 Jan 2018 06:57:35 +0000 [thread overview]
Message-ID: <5A4B2D5F.8090505@youngman.org.uk> (raw)
In-Reply-To: <CAJtTb3GYuEL-tco3Uy7L0G3ssTFez3=Qwghd5DzqTU5y-snh3Q@mail.gmail.com>
On 02/01/18 03:49, Amy Chiang wrote:
> I didn't specify --backup-file because I thought mdadm would give me a
> warning if there's a possibility that I might lose my data if this
> operation crash.
I'm slightly surprised at your results (although I shouldn't be :-).
Backup files are now almost entirely legacy - a modern setup should
pretty much never need them - which is why I'm surprised at your
results, I would have expected mdadm to ignore the backup-file option.
In the old days, a reshape used to copy a stripe to backup, and then
rewrite it. Rinse, lather and repeat. So the i/o overhead was high. Now,
with "data offset" and superblock 1, mdadm calculates where the reshaped
array is going to be, then starts copying from the old to array to where
the new array does not overlap the old array. This makes a window where
there are two copies of the data. When it runs out of space, it moves
the window to create more space and carries on copying. As you can see,
this is a lot less work ...
Cheers,
Wol
prev parent reply other threads:[~2018-01-02 6:57 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-02 3:49 conf->min_offset_diff calculation timing of growing raid5 Amy Chiang
2018-01-02 6:57 ` Wols Lists [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=5A4B2D5F.8090505@youngman.org.uk \
--to=antlists@youngman.org.uk \
--cc=amychiang@qnap.com \
--cc=linux-raid@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).