From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Boldi Subject: Re: RAID0 performance question Date: Fri, 2 Dec 2005 22:53:17 +0300 Message-ID: <200512022253.17282.a1426z@gawab.com> References: <437E2CB6.2030903@xss.co.at> <200511272040.47644.a1426z@gawab.com> <041e01c5f605$6a7c0830$0400a8c0@dcccs> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <041e01c5f605$6a7c0830$0400a8c0@dcccs> Content-Disposition: inline Sender: linux-raid-owner@vger.kernel.org To: JaniD++ Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids JaniD++ wrote: > > > > > > But the cat /dev/md31 >/dev/null (RAID0, the sum of 4 nodes) > > > > > > only makes ~450-490 Mbit/s, and i dont know why.... > > > > > > > > > > > > Somebody have an idea? :-) > > > > > > > > > > Try increasing the read-ahead setting on /dev/md31 using > > > > > 'blockdev'. network block devices are likely to have latency > > > > > issues and would benefit from large read-ahead. > > > > > > > > Also try larger chunk-size ~4mb. > > But i don't know exactly what to try. > increase or decrease the chunksize? > In the top layer raid (md31,raid0) or in the middle layer raids (md1-4, > raid1) or both? > What I found is that raid over nbd is highly max-chunksize dependent, due to nbd running over TCP. But increasing chunksize does not necessarily mean better system utilization. Much depends on your application request size. Tuning performance to maximize cat/dd /dev/md# throughput may only be suitable for a synthetic indication of overall performance in system comparisons. If your aim is to increase system utilization, then look for a good benchmark specific to your application requirements which would mimic a realistic load. -- Al