From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marco Subject: Re: raid1 performance Date: Mon, 26 Jul 2010 09:37:20 +0000 (GMT) Message-ID: <23123.42111.qm@web28503.mail.ukl.yahoo.com> References: <443220.14357.qm@web28508.mail.ukl.yahoo.com> <20100725211926.7547c12e@natsu> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Return-path: In-Reply-To: <20100725211926.7547c12e@natsu> Sender: linux-raid-owner@vger.kernel.org To: Roman Mamedov Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids >> doing a simple performance tests i obtained some very unexpected results: if >> i issue hdparm -t /dev/md2 i obtain 61 - 65 MB/s while issuing the same test >> directly on the partitions which compose md2 (/dev/sda3 and /dev/sdb3) i >> obtain 84 - 87 MB/s. I didn't expect a so big difference between md2 and one >> of its member. What can cause this difference ? > >Maybe their read-ahead settings are different? >Check out "blockdev --getra /dev/md2", and compare that with the same >setting of the member disks. You can experiment with changing it by using >"--setra" as well. Hi Roman, thank you for your hint, I verified the read-ahead settings and they are the same for all the block devices involved in the test: the value is 256 for all /dev/sd?? and for all /dev/md? there should be something else which is influencing raid 1 performance. Have someone of you ever had a similar issue ? thank you Marco