On Tue, Dec 11, 2001 at 03:34:37PM +0100, Wilko Bulte wrote: > On Tue, Dec 11, 2001 at 11:06:33AM +1030, Greg Lehey wrote: > > 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.
Here some real world statistics with UFS softupdates: Plex d1.p0: Size: 8736473088 bytes (8331 MB) Subdisks: 3 State: up Organization: striped Stripe size: 256 kB Part of volume d1 Reads: 83546 Bytes read: 258429952 (246 MB) Average read: 3093 bytes Writes: 100109 Bytes written: 818750464 (780 MB) Average write: 8178 bytes Multiblock: 279 (0%) Multistripe: 82 (0%) Subdisk 0: d1.p0.s0 state: up size 2912157696 (2777 MB) Subdisk 1: d1.p0.s1 state: up size 2912157696 (2777 MB) Subdisk 2: d1.p0.s2 state: up size 2912157696 (2777 MB) You can easily see that the number of Multistripe transactions are unnoticeable low. Here another case with 64k stripe size: Plex d7.p0: Size: 36419796992 bytes (34732 MB) Subdisks: 2 State: up Organization: striped Stripe size: 64 kB Part of volume d7 Reads: 934001 Bytes read: 3718752768 (3546 MB) Average read: 3981 bytes Writes: 220293 Bytes written: 3702993920 (3531 MB) Average write: 16809 bytes Multiblock: 50037 (4%) Multistripe: 25047 (2%) Subdisk 0: d7.p0.s0 state: up size 18209898496 (17366 MB) Subdisk 1: d7.p0.s1 state: up size 18209898496 (17366 MB) You can see that even we have an absolute extrem situation the number of multistripe transactions is still very low. But a value of 384k would be a much better value for other reasons. You may want to compare the multistripe number with the multiblock number and yes it doesn't look that good anymore, but you also see that the change from 64k to 256k get much better results, while the average transaction size is 5865 bytes for the first case and 6429 bytes for the second - not that different. Most of my plexes are concat anyway. -- B.Walter COSMO-Project http://www.cosmo-project.de [EMAIL PROTECTED] Usergroup [EMAIL PROTECTED] To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-current" in the body of the message