From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Robinson Subject: Re: Performance of a software raid 5 Date: Tue, 21 Apr 2009 01:52:54 +0100 Message-ID: <49ED18E6.1090301@anonymous.org.uk> References: <49ED096E.1000002@anonymous.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Johannes Segitz Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 21/04/2009 01:10, Johannes Segitz wrote: > On Tue, Apr 21, 2009 at 1:46 AM, John Robinson > wrote: >> I would have thought it's because you're running in degraded mode and one in >> 3 sectors is having to be regenerated from the parity. It still seems a bit >> slow, though. > > i don't think that that is a problem. The data is there without > redundancy so i can't see > how there would be the need to calculate anything There's no redundancy but it's still the RAID-5 4-disc layout with 3 data and 1 parity, the parity on a different disc in each stripe. In your case with a missing disc, for 3 stripes in 4 you have 2 data and 1 parity. Of course the parity is having to be calculated when you're writing, and whatever would be written to your missing disc is being discarded. On the other hand if you were using RAID-0 over 3 discs there would be no need to calculate anything. Cheers, John.