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 20:36:49 +0000 (UTC) Message-ID: References: <515C2C3C.3020400@hardwarefreak.com> <515C73B3.5060704@arcor.de> 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 > > 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 I'm very sorry but now i can't confirm anymore that stripe_cache_size helps. My test was to short. With every minute the IOPS decrease. So stripe_cache_size does only help for very short tests. I will provide details in another post. Peter