From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Bryan J. Smith" Subject: Re: mkfs options for a 16x hw raid5 and xfs (mostly large files) Date: Wed, 26 Sep 2007 10:11:56 -0700 (PDT) Message-ID: <673292.62672.qm@web32906.mail.mud.yahoo.com> References: Reply-To: b.j.smith@ieee.org Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Justin Piszcz , Bryan J Smith Cc: xfs-bounce@oss.sgi.com, Ralf Gross , linux-xfs@oss.sgi.com, linux-raid@vger.kernel.org List-Id: linux-raid.ids Justin Piszcz wrote: > I have a question, when I use multiple writer threads (2 or 3) I > see 550-600 MiB/s write speed (vmstat) but when using only 1 thread, > ~420-430 MiB/s... It's called scheduling buffer flushes, as well as the buffering itself. > Also without tweaking, SW RAID is very slow (180-200 > MiB/s) using the same disks. But how much of that tweaking is actually just buffering? That's a continued theme (and issue). Unless you can force completely synchronous writes, you honestly don't know. Using a larger size than memory is not anywhere near the same. Plus it makes software RAID utterly n/a in comparison to hardware RAID, where the driver is waiting until the commit to actual NVRAM or disc is complete. -- Bryan J. Smith Professional, Technical Annoyance b.j.smith@ieee.org http://thebs413.blogspot.com -------------------------------------------------- Fission Power: An Inconvenient Solution