In reply to Thomas.

Good question, Thomas, thanks!

First, I’d like to thanks my colleagues and Cisco Services SAN experts, Venkat Kirishnamurthyi and Jing Luo, for their insights here.

It varies depends on the OS you are loading, the hardware it is running and iSCSI software or hardware and physical connections.
For disk timeout on Windows, it can be configured in OS. For iSCSI, It is usually set as 60 seconds.

There are some implications of this, however.

Firstly, a consistent 40 ms latency is not really optimal in any situation. Even though the SCSI timeout is typically set to 60 seconds for Windows servers, you are going to have a very poorly performing system given the 40 ms latency. The fact that you are not getting a blue screen at 40ms is the only saving grace in this situation. Plus because of the 40 ms latency you will at some point of time start running out of buffers (TCP) leading to dropped packets and this will result in re trying of I/O further leading to very poor I/O performance.

Secondly, most applications expect a sub 10 ms latency for disk access. Oracle for example expects the I/O to complete with 3- 6 ms for optimal performance. Given the application requirements, you will have application issues making it an unworkable solution.

Hope this helps!
Stephen