From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Dan Williams" Subject: Re: What is the exacting meaning of Striped_Cache_Size? Date: Sun, 21 Jan 2007 23:06:37 -0700 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Disposition: inline Sender: linux-raid-owner@vger.kernel.org To: Liang Yang Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 1/21/07, Liang Yang wrote: > Hello, > > I have tried to increase the Striped_Cache_Size from 256 (default for my > MD-RAID5 array) to 8192, it does improve the MD-RAID5 Write performance > which varies with the size of I/O packet. > > However, I'm still not very clean the meaning and the potential performance > impact of this Striped_Cache_Size? Is the unit for this parameter Byte or > KiloByte? > > Could anyone here explain with a little bit more details? > stripe_cache_size is the number of stripes in the cache. Each stripe (strip) is composed one PAGE_SIZE block per disk. If your page size is 4k and you have 4 disks in your array then a stripe_cache_size of 256 is 4k * 4 * 256 = 4MB. Increasing this number increases the chances that a write to the array will not generate reads to satisfy the parity calculation. > Thanks, > > Liang > Regards, Dan