Hi Mike,
You are using a very small chunk size. Increase this number to 128. I
think you may need to remake the array though. This is kind of silly
since in RAID-1, the data isn't laid out any differently for different
chunk sizes as other raid personalities are. It would be nice to be able
to just edit the radtab file and have it automagically change.
The significance of the chunk size is this. The RAID-1 personality has a
read balancing mechanism that tries to use the same drive so long as the
requests are sequential and not bigger than the chunk size. With a chunk
size of 4, the raid driver is breaking the read requests into 4KB
chunks, then switching to the next disk which is hardly optimal. A value
of 128 is much better. For bonnie tests, the larger the better, but
bonnie is not a real world test. I find 128 a good compromise.
<>< Lance.
Mike Black wrote:
>
> I'm a little confused on RAID1...running 2.2.11 with
> raid0145-19990824-2.2.11.bz2 on a PII/233
>
> I just set up a mirror this weekend on an IDE RAID1 - two 5G disks on the
> same IDE bus (primary and master).
>
> I was under the impression that I shouldn't see any slowdown and maybe even
> a speedup but, alas, it is not so.
>
> Here's the hparm test (ran several times -- similar results each time):
>
> /dev/hda:
> Timing buffer-cache reads: 64 MB in 0.95 seconds =67.37 MB/sec
> Timing buffered disk reads: 32 MB in 3.28 seconds = 9.76 MB/sec
>
> /dev/md0:
> Timing buffer-cache reads: 64 MB in 0.85 seconds =75.29 MB/sec
> Timing buffered disk reads: 32 MB in 6.10 seconds = 5.25 MB/sec
>
> It looks like I've lost half of the bandwidth on disk reads. Did I miss
> something?? Here's the raidtab entry:
>
> raiddev /dev/md0
> raid-level 1
> nr-raid-disks 2
> nr-spare-disks 0
> persistent-superblock 1
> chunk-size 4
>
> device /dev/hda1
> raid-disk 0
> device /dev/hdb1
> raid-disk 1
>
> ________________________________________
> Michael D. Black Principal Engineer
> [EMAIL PROTECTED] 407-676-2923,x203
> http://www.csi.cc Computer Science Innovations
> http://www.csi.cc/~mike My home page
> FAX 407-676-2355
