From: Tomasz Chmielewski <tch@virtall.com>
To: "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
Subject: RAID-1 - suboptimal write performance?
Date: Fri, 16 May 2014 16:48:15 +0100 [thread overview]
Message-ID: <20140516164815.1c33149b@s9> (raw)
While doing rsyncs of large archives from one RAID-1 btrfs filesystem
to another RAID-1 btrfs filesystem:
btrfs filesystem 1: sda + sdb (RAID-1), being copied to:
btrfs filesystem 2: sdc + sdd (RAID-1)
Server has 32 GB RAM
I can observe the following:
>From time to time, rsync "freezes", while there is high IO on only *one*
of write drives.
To reproduce:
dd if=/dev/urandom of=/mnt/btrfs1/bigfile.img bs=1M count=10000; sync
# cp should work, too, but won't show copy speed/progress
rsync -a -v --progress /mnt/btrfs1/bigfile.img /mnt/btrfs2/
In another terminal, run iostat -m 1:
1) a few seconds of writes to only one RAID-1 member:
Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
sdc 355.00 0.00 177.50 0 177
sdb 0.00 0.00 0.00 0 0
sdd 0.00 0.00 0.00 0 0
sda 0.00 0.00 0.00 0 0
2) then, a few seconds of writes to the other RAID-1 member:
Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
sdc 0.00 0.00 0.00 0 0
sdb 0.00 0.00 0.00 0 0
sdd 351.00 0.00 175.50 0 175
sda 0.00 0.00 0.00 0 0
Is it optimal behaviour? With software RAID-1, I'm seeing writes to
both devices at the same time.
Also, what happens when the system crashes, and one drive has several
hundred megabytes data more than the other one?
--
Tomasz Chmielewski
http://wpkg.org
next reply other threads:[~2014-05-16 15:48 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-16 15:48 Tomasz Chmielewski [this message]
2014-05-16 18:06 ` RAID-1 - suboptimal write performance? Calvin Walton
2014-05-16 20:41 ` Tomasz Chmielewski
2014-05-16 21:36 ` Austin S Hemmelgarn
2014-05-18 18:49 ` Brendan Hide
2014-05-23 12:57 ` Roman Mamedov
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