iScsi Performance Test
Here some useful tips:
What/kind how fast are the drives?
What kind of numbers are you getting from the Host Server with hdparm?
You should see a significant increase of performance after enabling write caching on the target (details depends on the implementation) and your disks.
The price however is that this will endanger data integrity (especially if you run databases) in the case of a power outage or a system hang of the SAN, as data which is thought to have been permanently written to disk, only resided in volatile DRAM.
To mitigate this risk, you should use a controller with BBWC (battery-backed write cache) where data would survive a power outage for a while (typically 1-2 days).
hdparm -W 1 /dev/sda hdparm -W 1 /dev/sdb
vmstat(watch to wait and I/O ops)
scenarios with iometer: 1) sequential read/write -- this should give nice, fat numbers. 2) random access to the drive -- here you should be in for a land of hurt. Setup a file for tests large enough to force it to be pushed out of cache of the virtual machine.