From: Li Wang <liwang@ubuntukylin.com>
To: ceph-devel@vger.kernel.org
Cc: Sage Weil <sage@inktank.com>
Subject: 4x write amplification?
Date: Wed, 10 Jul 2013 10:08:37 +0800 [thread overview]
Message-ID: <51DCC225.1050700@ubuntukylin.com> (raw)
Hi,
We did a simple throughput test on Ceph with 2 OSD nodes configured
with one replica policy. For each OSD node, the throughput measured by
'dd' run locally is 117MB/s. Therefore, in theory, the two OSDs could
provide 200+MB/s throughput. However, using 'iozone' from clients we
only get a peak throughput at around 40MB/s. Is that because a write
will incur 2 replica * 2 journal write? That is, writing into journal
and replica doubled the traffic, respectively, which results in a total
4x write amplification. Is that true, or our understanding is wrong,
and some performance tuning hint?
Cheers,
Li Wang
next reply other threads:[~2013-07-10 2:08 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-10 2:08 Li Wang [this message]
2013-07-10 17:43 ` 4x write amplification? Gregory Farnum
2013-07-11 8:23 ` Oleg Krasnianskiy
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