From: Peter Rabbitson <rabbit+list@rabbit.us>
To: Michael Guntsche <mike@it-loops.com>
Cc: Maurice Hilarius <maurice@harddata.com>, linux-raid@vger.kernel.org
Subject: Re: Severe slowdown with LVM on RAID, alignment problem?
Date: Fri, 29 Feb 2008 11:37:58 +0100 [thread overview]
Message-ID: <47C7E086.5080203@rabbit.us> (raw)
In-Reply-To: <872d9b69db95a1b08319e935595743cc@localhost>
Michael Guntsche wrote:
>
> Is it possible that my computer is just too slow to get good read results?
unlikely
> While reading is a little bit faster it's nowhere near the speed I get on
> md0 itself.
>
I would guess that you did not set the correct read-ahead values for the LV.
If you do not specify anything it will default to 128k (256 sectors), which is
terribly small for sequential reads. On the contrary the MD device will do
some clever calculations and set its read-ahead correctly depending on the
raid level and the number of disks. Do:
blockdev --setra 65536 <your lv device>
and run the tests again. You are almost certainly going to get the results you
are after.
Peter
next prev parent reply other threads:[~2008-02-29 10:37 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-02-29 8:12 Severe slowdown with LVM on RAID, alignment problem? Michael Guntsche
2008-02-29 10:37 ` Peter Rabbitson [this message]
2008-02-29 10:45 ` Michael Guntsche
2008-03-01 20:45 ` Bill Davidsen
2008-03-01 21:26 ` Michael Guntsche
2008-03-02 20:14 ` Bill Davidsen
2008-03-04 19:52 ` Severe slowdown with LVM on RAID, alignment problem? - Autodetect? Janek Kozicki
[not found] <47C75436.9010301@harddata.com>
2008-02-29 7:37 ` Severe slowdown with LVM on RAID, alignment problem? Michael Guntsche
-- strict thread matches above, loose matches on Subject: below --
2008-02-29 0:05 Michael Guntsche
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=47C7E086.5080203@rabbit.us \
--to=rabbit+list@rabbit.us \
--cc=linux-raid@vger.kernel.org \
--cc=maurice@harddata.com \
--cc=mike@it-loops.com \
/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).