SCSI disk speed inconsistency

I get a read speed of 69MBps from my SCSI disk and a write speed of 49MBps from the same. An IOMeter benchmark on the net says that 68MBps is the sustained speed for a write.

Could someone tell me how to increase my IO speed?

I have a Linux Kernel 2.6 in a RedHat Enterprise Linux WS 4 and I used the foll. Read : sg_dd if=/dev/sdb of=/dev/null bs=262144 count=1024 dio=1
Write: sg_dd if=/dev/zero of=/dev/sdb bs=262144 count=1024 dio=1

Karthik,
For accurate timing with "sd" devices use "odir=1" rather than "dio=1". "dio=1" only applies to sg devices so it has no effect in your above example. [Perhaps I should add a warning about this in sg_dd.]

Also with sg_dd you should use "bs=512" and read about the "bpt=<n>" option in the man page. Also look at the "blk_sgio=0|1" and the "time=1" option.

Doug Gilbert