On Sunday 28 January 2007 08:45, Brian Candler wrote:
> On Sun, Jan 28, 2007 at 12:29:21AM -0800, Joe wrote:
> > Why is the write performance of my RAID controller so slow?
>
> ...
>
> > (write test running bsd kernel)
> > # dd if=/dev/zero of=/data/testfile count=20000 bs=128k
> > 20000+0 records in
> > 20000+0 records out
> > 2621440000 bytes transferred in 113.978 secs (22999380 bytes/sec)
>
> That's about 22MB per second. Sounds plausible to me, given that RAID5
> arrays intrinsically have very poor write performance. What value were you
> expecting to see?
This is what I see on a DL 380 G4. It has two 300GB drives in RAID1
configuration and 4 300 GB drives on RAID 5 configuration.:
RAID5 with 4 300GB drives
# dd if=/dev/zero of=testfile count=20000 bs=128k
20000+0 records in
20000+0 records out
2621440000 bytes transferred in 31.360 secs (83589627 bytes/sec)
RAID 1 with 2 300 GB drives
#dd if=/dev/zero of=testfile count=20000 bs=128k
20000+0 records in
20000+0 records out
2621440000 bytes transferred in 43.803 secs (59845997 bytes/sec)
bioctl -h ciss0 gives me
bioctl: Can't locate ciss0 device via /dev/bio
If possible, please let me know what has to be set up to get the info from
bioctl.
sysctl hw gives me
hw.machine=i386
hw.model=Intel(R) Xeon(TM) CPU 3.80GHz ("GenuineIntel" 686-class)
hw.ncpu=1
hw.byteorder=1234
hw.physmem=2147000320
hw.usermem=2146467840
hw.pagesize=4096
hw.disknames=sd0,sd1,cd0,fd0
hw.diskcount=4
hw.cpuspeed=3801
hw.vendor=HP
hw.product=ProLiant DL380 G4
It does not give me the type of output hw.sensors.0 etc. If possible, please
let me know how to get this also. I can then run another test that makes it
more comparable.
>
> For comparison, what do you get for the same test but for read speed? i.e.
>
> # dd if=/data/testfile of=/dev/null bs=128k
>
> RAID5 writes are slow because a single block write involves 4 disk
> operations (read old data block, read old parity, write new data block,
> write new parity). A non-volatile write-through cache can speed things up
> to a degree though.
>
> If you want high write performace, try setting up your six-disk array as
> three separate mirrored pairs, or as a single RAID-01 (strip/mirror) and
> see what you get. Of course your available storage size will be reduced to
> 3/5ths of what it was.
>
> Regards,
>
> Brian.
>
>
> !DSPAM:1,45bcb760150711234514069!
--
Vijay Sankar
ForeTell Technologies Limited
59 Flamingo Avenue, Winnipeg, MB, Canada R3J 0X6
Phone: +1 (204) 885-9535, E-Mail: [EMAIL PROTECTED]
