Large Sequential Reads Being Broken Up. Why?

["Martin W. Schlining III" <mschlining@datadirectnet.com>]

I am running a program on my Linux box which is asking for 2M IO (reads 
and writes) with the file handle being opened with the O_DIRECT flag. 
However, the IO being put out on the wire is no larger than 512K.  My 
target device is the SCSI block device (/dev/sdb in this case). What is 
preventing me from getting large IO through the SCSI block layer? How 
can I fix it?

The sg device can achieve the 2M IO size, so I know its at least 
possible. How can I improve the IO size for the SCSI block layer?

Details:

Dell 2850 server with dual Xeons, 1G RAM
OS: Linux racerx 2.6.11.4-21.10-smp #1 SMP Tue Nov 29 14:32:49 UTC 2005 
x86_64 x86_64 x86_64 GNU/Linux
Emulex LP11000 Fibre Channel HBA using driver version 8.0.13 (changing 
the driver hasn't helped, so far)
I set the lookahead value pretty large to improve read performance 
(hdparm -a)
The scheduler for this device is anticipatory.

Any ideas?

Thanks,
Martin Schlining