On Thu, 28 Oct 1999, Mika Kuoppala wrote:
> Here is my results for Raid-1 read performance weirdness:
>
> Raid 1: Chunk size 4k: /dev/md1:
>
> -------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
> raid1ch4 1000 1651 97.1 15473 81.2 6408 54.8 1769 99.4 8317 30.5 136.2 6.4
>
>
> Non raid partition: /dev/sda4:
>
> -------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
> sda4_fdc 1000 1713 99.7 15432 58.7 6202 53.0 1781 99.5 15095 47.3 126.5 4.5
>
>
> In short, Raid-1 performance drops to almost 1/2 of the
> performance of the non raid one device.
>
> There is definitely something weird in raid-1 code if
> others are getting same results. If you are, post them !!!
Not nearly as bad here...
-------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
non-raid 400 8927 67.6 10924 25.0 3620 16.7 7765 53.8 10036 17.2 103.3 3.8
-------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
raid1 400 8502 65.0 10236 18.3 3502 19.1 7646 53.2 8882 16.2 144.6 5.2
though I was surprised to find reading from the RAID1 to be slower at all.
My config is similar to Mika's, with kernel 2.2.11-ac3, an aic7880 and a
pair of UW IBM DDRS-34560D disks (with CTQ enabled, queue depth 32).
-Andy
