From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Brown Subject: Using of RAID10,offset for faster writes Date: Sat, 09 Apr 2011 14:03:21 +0200 Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids During a discussion about RAID in another context (a Linux newsgroup), I began thinking about the speeds of the different RAID10 layouts for different usages. RAID10,far is often the fastest choice for general use - you get striped reads for large reads, and access times are good because you can get the data from either disk. The disadvantage is that writes involve a lot of extra head movement, as you need copies of the data on two widely separated areas on the each disk. But for general use, you read a lot more often than you write, so the tradeoff is worth it. In the discussion we were looking particularly at swap space on RAID. This is a usage that requires a lot of writing, especially small writes. Using the RAID10,offset layout should give you most of the benefits of RAID10,far when it comes to reading - you don't get quite as efficient block reads for large reads, but you can still do a lot of striping in the reads. And writes will involve far less head movement, and so should complete faster. Has anyone tried this, or done any benchmarking?