On Wed, 26 May 1999 [EMAIL PROTECTED] wrote:
>
> Yes, I guess you're right that the way raid-1 stripes the reads doesn't
> necessarily yield higher read performance after all... Here's a little
> test I did:
>
> raid-0 on two disks:
> -------Sequential Output-------- ---Sequential Input-- --Random--
> -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
> Machine MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU
> 900 6160 97.1 21710 73.3 8559 52.5 7841 94.2 23977 63.9 157.3 5.5
>
> raid-1 on the same disks:
> -------Sequential Output-------- ---Sequential Input-- --Random--
> -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
> Machine MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU
> 470 5801 94.6 11719 39.5 5264 32.5 6931 83.0 11861 34.8 167.4 4.7
>
> Hmm.... I know that raid-1 does distribute the reads to both disks, so I would
> think that read-performance should increase. But it seems like it doesn't. At
> least not in this case. Btw. the disks where on separate SCSI controllers.
RAID1 won't increase sequential read speeds, but it *will* increase the
number of I/O operations you can perform concurrently, which is generally
a much more important factor in performance than raw I/O bandwidth.
Notice that RAID1's random seek performance is similar to RAID0's
performance. Odds are, testing with a single (non-RAID) drive would yield
similar bandwidth number to RAID1, but only ~80 I/O operations per second.
Scott
