Quote Originally Posted by Robotbeat
Block I/O is better. Fewer caching layers (I think), lower latency. In some circumstances, that means cached I/O can be a little slower, but if you have a fast back-end (a decent RAID card), it works fine. In fact, in some cases, File I/O just gets in the way.
I agree. Believe it or not... my machines have a great hardware backend and 32GB of RAM each, but File I/O just couldn't cut it.

I have a simple setup with 2 ESX servers and 2 DSS servers, each ESX targets both DSS and has an even split of VMFS volumes on each DSS.

After switching to Block I/O... Storage vMotion, vMotion, etc all sped up greatly(10x faster in some cases), barely increased "High Disk Latency" counter on the ESX servers during storage moves.

Overall I am much happier using Block I/O.