What does it mean? What do I do about it?
Measures the time to create a 100MB file without buffered writes. Transaction notes are written to disk synchronously and poor synchronous IO performance will be reflected in poor transaction throughput.
< 10 - Performance is inexcusably bad. Replace this IO subsystem immediately
< 20 - Performance is barely acceptable.
< 50 - Performance is "ok" if the system is not very demanding.
>= 50 - Performance is excellent.
Poor synchronous IO is an inherent characteristic of RAID5, RAID6, SAN, NAS and similar configurations.