iSCSI read/write cost difference

[mingz <mingz@ele.uri.edu>]

I recently did some experiments on iSCSI benchmarking. I used the UNH iSCSi 
ref18_03 implementation and use a ram based scsi device for iscsi target use. 
so there is no any disk overhead.

I used a linux kernel module to send fixed size read/write requests to iscsi 
initiator, which eventually will be filled by iscsi target. i use interl 
pro1000 gigabit nic and intel 470 gigabit switch. and both initiator and 
target use same type piii 866 pc with 1g ram. 

now the IOPS result shows that 

		2k		4k		8k		16k		32k
read		1975	1781	1557	1081	767
write 	2877	2225	1588	812		533

for small reuqests, read is slower than write, while for large requests, read 
is faster than write. i redo the experiments on another enviroment, also get 
similar results.

can anybody explain why this happens?

thanks a lot.


ming