From mboxrd@z Thu Jan 1 00:00:00 1970 From: Martin Wilck Subject: Re: RAID 5 doesn't scale Date: Wed, 03 Apr 2013 20:23:47 +0200 Message-ID: <515C73B3.5060704@arcor.de> References: <515C2C3C.3020400@hardwarefreak.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <515C2C3C.3020400@hardwarefreak.com> Sender: linux-raid-owner@vger.kernel.org To: stan@hardwarefreak.com Cc: Peter Landmann , linux-raid@vger.kernel.org List-Id: linux-raid.ids On 04/03/2013 03:18 PM, Stan Hoeppner wrote: > You didn't mention your stripe_cache_size value. It'll make a lot of > difference. Make sure it's at least 4096. The default is 256. I'm not getting it - why would stripe cache size matter in a random read/write test? If the disks are large enough and the pattern is really random, the cache should hardly ever be hit (s_c_z = 4096 =^ 16MB cache per disk, that's 0.01% of disk size for a 160GB SSD). I read that Peter confirmed the influence of stripe_cache_size, but I'd like to understand why it matters in this case. Martin