From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Rabbitson Subject: Re: Help with chunksize on raid10 -p o3 array Date: Mon, 12 Mar 2007 15:46:19 +0100 Message-ID: <45F567BB.3090804@rabbit.us> References: <45ED4FE1.5020105@rabbit.us> <17908.55047.408840.852816@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <17908.55047.408840.852816@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Neil Brown wrote: > The different block sizes in the reads will make very little > difference to the results as the kernel will be doing read-ahead for > you. If you want to really test throughput at different block sizes > you need to insert random seeks. > Neil, thank you for the time and effort to answer my previous email. Excellent insights. I thought that read-ahead is filesystem specific, and subsequently I would be safe to use the raw device. I will definitely test with bonnie again. >> * Why although I have 3 identical chunks of data at any time, dstat >> never showed simultaneous reading from more than 2 drives. Every dd run >> was accompanied by maxing out one of the drives at 58MB/s and another >> one was trying to catch up to various degrees depending on the chunk >> size. Then on the next dd run two other drives would be (seemingly >> random) selected and the process would repeat. > > Poor read-balancing code. It really needs more thought. > Possibly for raid10 we shouldn't try to balance at all. Just read > from the 'first' copy in each case.... Is this anywhere near the top of the todo list, or for now raid10 users are bound to a maximum read speed of a two drive combination? And a last question - earlier in this thread Bill Davidsen suggested to play with the stripe_cache_size. I tried to increase it (did just two tests though) with no apparent effect. Does this setting apply to raid1/10 at all or it is strictly in the raid5/6 domain? If so, are there any tweaks apart from the chunk size and the layout that can affect raid10 performance? Once again thank you for the help. Peter