From mboxrd@z Thu Jan 1 00:00:00 1970 From: asho@chuany.net Subject: Re: Software RAID0 behaviour/performance on ATA drives Date: Fri, 25 Mar 2005 17:04:54 +0800 Message-ID: <20050325090454.GA8352@acer1200> References: <4242EAFB.9060008@nospam.com> <16963.37953.872779.652517@cse.unsw.edu.au> Mime-Version: 1.0 Content-Type: text/plain; charset=big5 Content-Disposition: inline In-Reply-To: <16963.37953.872779.652517@cse.unsw.edu.au> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids > > The raid0 driver is 'clever' at all. > It is given requests by the filesystem or mm subsystem, maps them to > the correct device/sector, and sends them straight on to the > appropriate driver. It never waits for requests, just maps and > forwards. > > So if the filesystem sends 128 4k read-ahead requests to the raid0 > driver it will forward each one to the relevant device and, depending > on chunk size etc, you might get, say, 32 4K requests sent to each of > 4 drives. The drives would (depending on the internals of the driver) > processes all these requests in parallel. > > In your example, if the filesystem or mm subsystem submitted writes > for 4 consecutive chunks on a two-drive raid0 array without waiting > for earlier ones to complete before submitting later ones, then they > would all get to the device driver in a timely fashion, and the device > driver(s) should be able to drive the two drives in parallel. > > So if the writer handles the required parallelism, and the devices > handle the required parallelism, then the raid0 layer won't interfere > at all. > NeilBrown Hi Neil I am curious about that, too. In my memory, the IDE Channel can only allow one IDE device read/write at once. If one driver(e.g. master) was writing, the second driver (e.g. slave) must wait until the master driver finished... If you were right, can I plug the two disk into the same IDE channel in raid 1 without losing any performance? Asho Yeh -- ~ Asho Yeh 'v' GnuPG-Key ID: 1CC92D7F // \\ Fingerprint: 192B 76FD 5643 6EE7 3DEC 9EAF 3088 48D2 1CC9 2D7F /( )\ ^`~'^