From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sevrin Robstad Subject: Re: bad performance on RAID 5 Date: Thu, 18 Jan 2007 21:47:02 +0100 Message-ID: <45AFDCC6.5030604@start.no> References: <45AE9640.1040500@start.no> <45AEA550.5070005@lucidpixels.com> <45AFBA3E.9070000@start.no> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7BIT Return-path: In-reply-to: Sender: linux-raid-owner@vger.kernel.org To: Mark Hahn Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Mark Hahn wrote: >>> Chunk Size : 256K > > well, that's pretty big. it means 6*256K is necessary to do a > whole-stripe update; your stripe cache may be too small to be effective. > >>> If they are on the PCI bus, that is about right, you probably should >>> be getting 10-15MB/s, but it is about right. If you had each drive >>> on its own PCI-e controller, then you would get much faster speeds. > > 10-15 seems bizarrely low - one can certainly achieve >100 MB/s > over the PCI bus, so where does the factor of 6-10 come in? > seems like a R6 resync would do 4 reads and 2 writes for every > 4 chunks of throughput (so should achieve more like 50 MB/s if the > main limit is the bus at 100.) > >> There are two controllers, 4 disks connected to one controller on the >> PCI-bus and 2 disks connected to the other controller. > > well, you should probably look at the PCI topology ("lspci -v -t"), > and perhaps even the PCI settings (as well as stripe cache size, > perhaps nr_requests, etc) > > I've tried to increase the stripe_cache_size a lot, no noticable difference. I set it to 8096.... [root@compaq md]# lspci -v -t -[0000:00]-+-00.0 VIA Technologies, Inc. VT8366/A/7 [Apollo KT266/A/333] +-01.0-[0000:01]----00.0 ATI Technologies Inc Rage 128 RF/SG AGP +-05.0 Silicon Image, Inc. SiI 3114 [SATALink/SATARaid] Serial ATA Controller +-07.0 Silicon Image, Inc. SiI 3114 [SATALink/SATARaid] Serial ATA Controller +-08.0 Realtek Semiconductor Co., Ltd. RTL-8169 Gigabit Ethernet +-11.0 VIA Technologies, Inc. VT8233 PCI to ISA Bridge \-11.1 VIA Technologies, Inc. VT82C586A/B/VT82C686/A/B/VT823x/A/C PIPC Bus Master IDE [root@compaq md]#