From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stan Hoeppner Subject: Re: Small chunk size read performance penalty Date: Sun, 18 Aug 2013 20:40:50 -0500 Message-ID: <521177A2.2010704@hardwarefreak.com> References: 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: Sender: linux-raid-owner@vger.kernel.org To: Ian Pilcher Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 8/18/2013 5:05 PM, Ian Pilcher wrote: > Can anyone point me to a good explanation of the read performance impact > of small (RAID-5 and RAID-6) chunk sizes? Can you elaborate on your workload that demonstrates this? Different workloads behave differently with different chunk sizes. > I understand why large chunks hurt write performance... Again this is workload dependent. Large chunks increase write and read performance for large streaming workloads. > The "read penalty" is definitely there; I can see it in the test data > from my NAS. I just don't understand *why* it's there. If you can see it, then please demonstrate this read penalty with numbers. You obviously have test data from the same set of disks with two different RAID5s of different chunk sizes. This is required to see such a difference in performance. Please share this data with us. -- Stan