From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Landmann Subject: Re: RAID 5 doesn't scale Date: Wed, 3 Apr 2013 21:12:59 +0000 (UTC) Message-ID: References: <515C2C3C.3020400@hardwarefreak.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids > Note also that you're doing 4KB random writes against RAID5. This is > going to generate substantial RMW cycles. The Intel X25-M G2 is not a > speed daemon. Its published max 4KB IOPS throughput is for purely > random writes, not the read+write pattern created by parity RMW. So > while your random read should get a nice jump with this test, your > random write may not improve as much. The limitation here is a function > of the SSD controller on the X25-M G2, not md/RAID5. If you test 5 > drives in md/RAID0 you'll see a bump in random write IOPS. > It seems so. I let fio run a bit longer and in each settings the ssd- performance decreased after few minutes. While mpstat still showed ~100% ssd- utilization.