I just ran sqlio while using an iscsi volume (only using a single 1Gb ethernet connection, jumbo frames not enabled). It was pretty slow for random read I/O in cache. In fact, it was about only 470 I/O when I ran it this way (with a 200MB test file):

sqlio -kR -s60 -frandom -o128 -b4 -LS -Fparam.txt

The param.txt file has only this in it: "H:\testfile.dat 1 0x0 200", which is where the test file is located (i.e. we are testing the D volume right now, which happens to be iSCSI) and how many threads to run (one) and the bitmask that sets processor affinity (does not apply, since there's only one core) and how big of a test file in megabytes. When I did both the FC volume and the iSCSI volume, I used NTFS with 4096Byte blocksize. The initiator is MS S/W iSCSI 2.08. The iSCSI target is block I/O mounted with writeback cache enabled. The FC volume uses 4096 byte blocksize.

Whereas when I use a FC volume over a 1Gb FC interface, it's about 14000 random read I/O.

I've done this a few times now, and it seems quite obvious that FC is far superior for random I/O reads from cache. Granted, I am only able to test one thread at a time right now, since my initiator side is only single-core. Oh well.

I tried running the same thing on the FC volume right after this test (but first running a sequential sqlio run to put the benchmark file in the DSS system cache, as in the iSCS volume test). I get over 14,000 random read I/Os!

BTW, the easiest way to make sure the whole benchmark test file is in the cache while using sqlio is to just run sqlio in sequential mode beforehand once or twice for a long enough for it to read the entire test file. If this were not a benchmark but a production environment with a cache large enough for, say, an entire mysql database to fit in, one could just "dd if=/dev/sda1 of=/dev/null bs=4k" to make sure everything is in cache before you start using it. This could be done on the DSS side or the client side. The DSS side would be a little faster, but it doesn't really matter that much, since you'd only rarely have to do it.


PS, I'll try to see what difference jumbo frames makes, if I can enable it.