Recently sp_blitz procedure on one of my OLTP servers returned alarming notification about high latency on one of the disks (more than 100ms per IO). Our chief storage guy didn’t understand what I was talking about – according to his measures, average latency is only about 15ms. In order to investigate the issue, I’ve recorded 2 snapshots of sys.dm_io_virtual_file_stats and calculated latency per read and write separately. Results appeared to be even more alarming: while for read average latency...(read more)