I recently came across an older article about defragmenting SANs (read it here). It includes interviews with analysts, SAN vendors (some pro-defrag, some against), and an employee from Diskeeper Corporation.
I was particulary impressed with the EMC’ers response:
“The SAN can’t do anything about the fact that Windows sees the file in 30 bits,” said Wambach. “That’s really something that is happening outside of the storage realm.”
He highlights the abstraction perfectly. SAN vendors claim that a defragmenter cannot correct fragmentation due to the fact it is abstracted from the physical blocks. We absolutely agree with this statement. And for that same reason, SANs cannot fix fragmentation in the NTFS file system, which causes excess and unnecessary overhead on the OS.