All of lore.kernel.org
 help / color / mirror / Atom feed
From: Andreas Klauer <Andreas.Klauer@metamorpher.de>
To: Reindl Harald <h.reindl@thelounge.net>
Cc: Adam Goryachev <mailinglists@websitemanagers.com.au>,
	Jeff Allison <jeff.allison@allygray.2y.net>,
	linux-raid@vger.kernel.org
Subject: Re: proactive disk replacement
Date: Tue, 21 Mar 2017 13:41:29 +0100	[thread overview]
Message-ID: <20170321124129.GA18865@metamorpher.de> (raw)
In-Reply-To: <8b108a89-9d17-63f0-de1c-80b17be4411a@thelounge.net>

On Tue, Mar 21, 2017 at 01:03:22PM +0100, Reindl Harald wrote:
> the IO of a RAID5/6 rebuild is hardly linear beause the informations 
> (data + parity) are spread all over the disks

It's not "randomly" spread all over. The blocks are always where they belong.

https://en.wikipedia.org/wiki/Standard_RAID_levels#/media/File:RAID_6.svg

It's AAAA, BBBB, CCCC, DDDD. Not DBCA, BADC, ADBC, ...

There is no random I/O involved here, at worst it will decide to not read 
a parity block because it's not needed but that does not cause huge/random
jumps for the HDD read heads.

> while in case of RAID1/10 it is really linear

Actually RAID 10 has the most interesting layout choices... 
to this day mdadm is unable to grow/convert some of these.

In a RAID 10 rebuild the HDD might have to jump from end to start.

Of course if you consider metadata updates (progress has to be 
recorded somewhere?) then ALL rebuilds regardless of RAID level 
are random I/O in a way.

But such is the fate of a HDD, it's their bread and butter. 
Any server that does anything other than "idle" does random I/O 24/7.

If there was no other I/O (because the RAID is live during rebuild) 
and no metadata updates (or external metadata) you could totally do 
RAID0/1/5/6 rebuilds with tape drives. That's how random it is.
RAID10 might need a rewind in between.

Regards
Andreas Klauer

  reply	other threads:[~2017-03-21 12:41 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-20 12:47 proactive disk replacement Jeff Allison
2017-03-20 13:25 ` Reindl Harald
2017-03-20 14:59 ` Adam Goryachev
2017-03-20 15:04   ` Reindl Harald
2017-03-20 15:23     ` Adam Goryachev
2017-03-20 16:19       ` Wols Lists
2017-03-21  2:33   ` Jeff Allison
2017-03-21  9:54     ` Reindl Harald
2017-03-21 10:54       ` Adam Goryachev
2017-03-21 11:03         ` Reindl Harald
2017-03-21 11:34           ` Andreas Klauer
2017-03-21 12:03             ` Reindl Harald
2017-03-21 12:41               ` Andreas Klauer [this message]
2017-03-22  4:16                 ` NeilBrown
2017-03-21 11:56           ` Adam Goryachev
2017-03-21 12:10             ` Reindl Harald
2017-03-21 13:13           ` David Brown
2017-03-21 13:24             ` Reindl Harald
2017-03-21 14:15               ` David Brown
2017-03-21 15:25                 ` Wols Lists
2017-03-21 15:41                   ` David Brown
2017-03-21 16:49                     ` Phil Turmel
2017-03-22 13:53                       ` Gandalf Corvotempesta
2017-03-22 14:12                         ` David Brown
2017-03-22 14:32                         ` Phil Turmel
2017-03-21 11:55         ` Gandalf Corvotempesta
2017-03-21 13:02       ` David Brown
2017-03-21 13:26         ` Gandalf Corvotempesta
2017-03-21 14:26           ` David Brown
2017-03-21 15:31             ` Wols Lists
2017-03-21 17:00               ` Phil Turmel
2017-03-21 15:29         ` Wols Lists
2017-03-21 16:55         ` Phil Turmel
2017-03-22 14:51 ` John Stoffel

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=20170321124129.GA18865@metamorpher.de \
    --to=andreas.klauer@metamorpher.de \
    --cc=h.reindl@thelounge.net \
    --cc=jeff.allison@allygray.2y.net \
    --cc=linux-raid@vger.kernel.org \
    --cc=mailinglists@websitemanagers.com.au \
    /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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.