From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stan Hoeppner Subject: Re: recommended way to add ssd cache to mdraid array Date: Wed, 16 Jan 2013 16:06:39 -0600 Message-ID: <50F7246F.2040004@hardwarefreak.com> References: <201212212357.19292.thomas@fjellstrom.ca> <201301142052.06390.thomas@fjellstrom.ca> <50F5157A.2080308@hardwarefreak.com> <201301152231.43704.thomas@fjellstrom.ca> Reply-To: stan@hardwarefreak.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <201301152231.43704.thomas@fjellstrom.ca> Sender: linux-raid-owner@vger.kernel.org To: thomas@fjellstrom.ca Cc: Tommy Apel Hansen , Chris Murphy , linux-raid Raid List-Id: linux-raid.ids On 1/15/2013 11:31 PM, Thomas Fjellstrom wrote: > That gets me thinking. Maybe try a test with the record test size set to the > stripe width, that would hopefully show some more accurate numbers. That will give you less accurate numbers, if you're looking for numbers that reflect real world performance. Again, in general, most real world writes are not stripe aligned, and not full width, especially with the insanely large 512KB chunk size. For all but a few workloads, storage should be designed and optimized assuming most writes will be unaligned or not full width, -not- assuming most will be full stripe writes. -- Stan