From: Peter Rabbitson <rabbit+list@rabbit.us>
To: linux-raid@vger.kernel.org
Subject: Suboptimal raid6 linear read speed
Date: Tue, 15 Jan 2013 23:33:01 +1100 [thread overview]
Message-ID: <20130115123301.GA11948@rabbit.us> (raw)
Hello,
Apologies in advance if this question has been answered before - I
perused the archives to no avail.
I am experiencing slow linear read from a bare raid6 device, while the
underlying drives are capable of saturating their capabilities. I can't
seem to find an explanation for this.
Regular parallel read from members:
===========
Imladris:~# echo 3 > /proc/sys/vm/drop_caches; sleep 3; for d in /dev/sd[abcd] ; do dd if=$d of=/dev/null bs=1M count=2048 & done
[1] 13953
[2] 13954
[3] 13955
[4] 13956
Imladris:~# 2048+0 records in
2048+0 records out
2147483648 bytes (2.1 GB) copied, 17.331 s, 124 MB/s
2048+0 records in
2048+0 records out
2147483648 bytes (2.1 GB) copied, 17.5719 s, 122 MB/s
2048+0 records in
2048+0 records out
2147483648 bytes (2.1 GB) copied, 18.47 s, 116 MB/s
2048+0 records in
2048+0 records out
2147483648 bytes (2.1 GB) copied, 18.6834 s, 115 MB/s
===========
Same sort of read from array itself:
===========
Imladris:~# echo 3 > /proc/sys/vm/drop_caches; sleep 3; dd if=/dev/md6 of=/dev/null bs=1M count=8192
8192+0 records in
8192+0 records out
8589934592 bytes (8.6 GB) copied, 34.9699 s, 246 MB/s
===========
I was expecting to see numbers in the neighborhood of 450 MB/s
My kernel: linux-image-3.2.0-4-rt-amd64 3.2.32-1 Linux 3.2 for 64-bit PCs, PREEMPT_RT
My raid6 parameters: http://paste.debian.net/224887/
My partition alignment: http://paste.debian.net/224888/
(reationale: 4k * 255 * 63, keeps both 4k sector drives aligned and older
partition utilities happy)
My disk parameters: http://paste.debian.net/224890/
Readaheads: http://paste.debian.net/224892/
Any ideas/suggestions welcome.
Cheers
next reply other threads:[~2013-01-15 12:33 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-15 12:33 Peter Rabbitson [this message]
2013-01-15 12:45 ` Suboptimal raid6 linear read speed Mikael Abrahamsson
2013-01-15 12:56 ` Peter Rabbitson
2013-01-15 16:13 ` Mikael Abrahamsson
2013-01-15 12:49 ` Phil Turmel
2013-01-15 12:55 ` Peter Rabbitson
2013-01-15 17:09 ` Charles Polisher
2013-01-15 19:57 ` keld
2013-01-16 4:43 ` Charles Polisher
2013-01-16 6:37 ` Tommy Apel Hansen
2013-01-16 9:36 ` keld
2013-01-16 16:09 ` Charles Polisher
2013-01-16 20:40 ` EJ Vincent
2013-01-15 23:17 ` Phil Turmel
2013-01-16 2:48 ` Stan Hoeppner
2013-01-16 2:58 ` Peter Rabbitson
2013-01-16 20:29 ` Stan Hoeppner
2013-01-16 21:20 ` Roy Sigurd Karlsbakk
2013-01-17 15:51 ` Mikael Abrahamsson
2013-01-18 8:31 ` Stan Hoeppner
2013-01-18 9:18 ` Mikael Abrahamsson
2013-01-18 22:56 ` Stan Hoeppner
2013-01-19 7:43 ` Mikael Abrahamsson
2013-01-19 22:48 ` Stan Hoeppner
2013-01-19 23:51 ` Maarten
2013-01-20 0:16 ` Chris Murphy
2013-01-20 0:49 ` Maarten
2013-01-20 1:37 ` Phil Turmel
2013-01-20 9:44 ` Chris Murphy
2013-01-20 6:26 ` Mikael Abrahamsson
2013-01-20 9:39 ` Chris Murphy
2013-01-20 16:55 ` Mikael Abrahamsson
2013-01-20 17:15 ` Chris Murphy
2013-01-20 17:17 ` Mikael Abrahamsson
2013-01-20 17:20 ` Chris Murphy
2013-01-19 23:53 ` Phil Turmel
2013-01-20 9:04 ` Wolfgang Denk
2013-01-20 19:28 ` Peter Grandi
2013-01-20 21:09 ` Mikael Abrahamsson
2013-01-20 21:50 ` Peter Grandi
2013-01-21 5:24 ` Mikael Abrahamsson
2013-01-21 14:40 ` Peter Rabbitson
2013-01-21 20:32 ` Peter Grandi
2013-01-21 20:55 ` Peter Grandi
2013-01-21 22:00 ` Peter Grandi
2013-01-19 13:21 ` Roy Sigurd Karlsbakk
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