From mboxrd@z Thu Jan 1 00:00:00 1970 From: Li Wang Subject: 4x write amplification? Date: Wed, 10 Jul 2013 10:08:37 +0800 Message-ID: <51DCC225.1050700@ubuntukylin.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from m59-178.qiye.163.com ([123.58.178.59]:58407 "EHLO m59-178.qiye.163.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753627Ab3GJCIr (ORCPT ); Tue, 9 Jul 2013 22:08:47 -0400 Sender: ceph-devel-owner@vger.kernel.org List-ID: To: ceph-devel@vger.kernel.org Cc: Sage Weil 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