On Wed, Dec 12, 2001 at 09:00:34AM +1030, Greg Lehey wrote: > On Tuesday, 11 December 2001 at 15:34:37 +0100, Wilko Bulte wrote: > > On Tue, Dec 11, 2001 at 11:06:33AM +1030, Greg Lehey wrote: > >> On Monday, 10 December 2001 at 10:30:04 -0800, Matthew Dillon wrote: > >>>
.. > >>> and will go down the drain for reads if you cross a stripe - > >>> something that is quite common I think. > >> > >> I think this is what Mike was referring to when talking about parity > >> calculation. In any case, going across a stripe boundary is not a > >> good idea, though of course it can't be avoided. That's one of the > >> arguments for large stripes. > > > > In a former life I was involved with a HB striping product for SysVr2 > > that had a slightly modified filesystem that 'knew' when it was > > working on a striped disk. And as it know, it avoided posting I/O s > > that crossed stripes. > > So what did it do with user requests which crossed stripes? Memory is dim, but I think the fs code created a second i/o to the driver layer. So the fs never sent out an i/o that the driver layer had to break up. In case of a pre-fetch while reading I think the f/s would just pre-fetch until the stripe border and not bother sending out a second i/o down. In the end all of this benchmarked quite favorably. Note that this was 386/486 era, with the classic SysV filesystem. -- | / o / /_ _ email: [EMAIL PROTECTED] |/|/ / / /( (_) Bulte Arnhem, The Netherlands To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-current" in the body of the message
