Hi, I've been using the sg3_util_.1.3's sg_dd, and
I'm running into some strange behaviors. I'm running
RedHat 9, 64bit, Linux 2.6. I have a qla2310 HBA
card, attached to it via Fiber Channel is a JMR JBOD
2G6, inside of it are 2 drives (Seagate Cheetah 15k.3
37GB (ST336753FC) and a Seagate Cheetah 15k 17GB
(ST318453FC)). The 37GB is mapped to /dev/sdb and
/dev/sg2, the 17GB is mapped to /dev/sdc and /dev/sg3.

I run the following:

>time sg_dd if=/dev/zero of=/dev/sdb bpt=128
count=1200000
->this finishes is around 10 seconds

>time sg_dd if=/dev/zero of=/dev/sdb bpt=129
count=1200000
->this finishes is around 17 seconds

I've tried this with different bpt, and it seems to go
slower when bpt is odd with both drives.

In addition, I wrote a simple program that uses
generic sg driver (SG_IO of ioctl) to write random
junk to a disk. When I write to the 37GB disk with a
bpt of 128, my transfer rate is around 175Mbs, but
when i perform the same operation/code on my 17GB, I
obtain 500Mbs. Read from the disks both yield 500Mbs.
Why such a big difference? and only on the write?

Any help is much appreciated. Thanks in advance.

-Ying