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
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