On Wed, 30 Jun 1999, D. Lance Robinson wrote:
> Try bumping your chunk-size up. I usually use 64. When this number is low,
> you cause more scsi requests to be performed than needed. If really big (
> >=256 ) RAID 0 won't help much.
Richard said in his original message that he's running IDE disks, not
SCSI.
> Richard Schroeder wrote:
>
> > Help,
> > I have set up RAID-0 on my Linux Redhat 6.0. I am using RAID-0
> > (striping) with two IDE disks (each disk on it's own IDE controller).
> > No problems in getting it running. However, my tests show I/O
> > performance seems to be worse than on a "normal" non-RAID filesystem. I
> > have tried different chunk-sizes to no avail. I must be missing
> > something. Shouldn't I be seeing a slight performance gain?
Richard, do you know if your disks are using DMA? Do a "hdparm -d
/dev/hda" (and also for /dev/hdc) to find out. If they're not, do "hdparm
-d1 /dev/hda" and "hdparm -d1 /dev/hdc".
I don't consider myself an authority on Linux software raid, or on IDE,
but from my experience setting the drives to use DMA makes all the
difference in the world in an IDE system. In contrast, adjusting
chunk-size may or may not get you a noticeable performance increase,
depending on how you use the array (a few really large files vs. many,
many small files).
On every Linux RAID0 system I've built, formatting the filesystem using 4k
blocks instead of the default 1k made a far greater difference in
performance than any chunk-size I tried (from 4 to 128). Do a "mke2fs -b
4096 /dev/md0".
Mike
--
Mike Tibor Univ. of Alaska Anchorage (907) 786-1001 voice
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