From mboxrd@z Thu Jan 1 00:00:00 1970 From: Justin Piszcz Subject: Re: Software RAID5 Horrible Write Speed On 3ware Controller!! Date: Wed, 18 Jul 2007 07:32:33 -0400 (EDT) Message-ID: References: <20070718110525.GF13772@boogie.lpds.sztaki.hu> <469DF8D3.8020908@theendofthetunnel.de> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Return-path: In-Reply-To: <469DF8D3.8020908@theendofthetunnel.de> Sender: linux-raid-owner@vger.kernel.org To: Hannes Dorbath Cc: Gabor Gombas , linux-ide-arrays@lists.math.uh.edu, xfs@oss.sgi.com, linux-raid@vger.kernel.org, linux@vger.kernel.org List-Id: linux-raid.ids On Wed, 18 Jul 2007, Hannes Dorbath wrote: > On 18.07.2007 13:19, Justin Piszcz wrote: >> For the HW RAID tests (2) at the bottom of the e-mail, no, I did not set >> nr_requests or use the deadline scheduler. >> >> For the SW RAID tests, I applied similar optimizations, I am probably not >> at the latest firmware. The main thing I wanted to use though was SW RAID >> because the card itself offers so many ports, however, with write speed >> being that slow I am not sure its a good idea. > > I think what you might be experiencing is that XFS can read su,sw values from > the MD device and will automatically optimize itself, while it can't do that > for the HW RAID device. It is absolutely essential to align your file system, > to prevent implicit reads, needed for parity calculations. > > Set su to the stripe size you have configured in your controller (like 128K) > and sw to 9 (for a 10 disk RAID 5 array). > > > -- > Regards, > Hannes Dorbath > Yes I agree here, but I guess my question is why is SW RAID5 so slow on the 3ware card? Justin.