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: Mon, 22 Jan 2007 09:36:36 -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: > Dan, > > Thanks for your reply. Still get two questions left. > > Suppose I have a MD-RAID5 array which consists of 8 disks. > 1. Do we need to consider the chunk size of the RAID array when we set the > value of Striped_Cache_Size? For example, if the chunk size is changed from > 64k to 256k, do we need to adjust the Striped_Cache_Size accordingly? > stripe_cache_size and the chunk size are completely independent settings. The chunk size only determines how much data will be accessed from one disk before proceeding to the next disk. > 2. The performance improvement of large size I/O packets (128k, 256k) is > larger than small size I/O packets (512B, 1KB) when I change the > Striped_Cache_Size. How do you explain the difference here? > With smaller I/Os the chances that you are staying within one stripe are higher so you would see less benefit of having more stripes in the cache. > Liang > Dan