[Sunhelp] Slow writes compared to reads with DiskSuite

[David Rouse]

We have a U250 providing file service for a bunch of Macintosh clients. 
The machine is running Solaris 2.6 and DiskSuite 4.2 and has two 
internal 4 GB drives (mirrored) for stuff like /, /var, etc. and four 9 
GB drives for client files. The four 9GB drives are arranged in a RAID 5 
through DiskSuite.

I had noticed that it takes longer for our clients to write to the 
server than to read from it, something like twice as long. A third-party 
software vendor suggested running the following tests to check the speed 
of our disks:

Write test -
dd if=/dev/zero bs=1024k of=tstfile count=1024

Read test -
dd if=tstfile bs=1024k of=/dev/null

I used 'time' to time the test and recorded the 'real' time. I averaged 
three runs and ran the tests during a quite time. To provide myself with 
comparison data I also ran the test on a stock, older U5 running Solaris 
7 and a U1 also running 2.6 and DiskSuite 4.2 with mirrored drives.

U5 --
Write: 223s
Read: 220s

U250's RAID --
Write: 417s
Read: 74s

U250's mirror --
Write: 149s
Read: 61s

U1's mirror --
Write: 95s
Read: 62s

Assuming that this was a fair test, I guess then it is normal to have 
asymmetrical reads v writes with DiskSuite. I'll also buy the 
differences between the U1 and U250 mirrors because the U1 has a better 
setup (more SCSI controllers) I also knew that a software RAID wouldn't 
provide blazing performance. But should the RAID 5 writes be this bad? 
Worse than the U5! What would a hardware RAID 5 (like the A1000) give 
us? Has anyone heard when Sun's RAID card would be available for the 
internal disks of a U250?

Thanks for any advice, etc.

--  
David Rouse
Network Manager
Goldsboro News-Argus