Some more observations:
- Microsoft's defrag APIs fully and safely support defragmentation of Exchange datastores without first shutting down Exchange services.
- While I agree that kicking off a defrag pass on a drive with a heavy I/O load can result in a slowdown in drive performance, it does NOT mean that it is unsafe to do - regardless of application (file serving, Exchange, SQL, etc...)
- I have searched for several years now for information from Microsoft indicating that it is unsafe to run a file-level defragmenter on drives where Exchange datastores/files are located and have yet to find any whatsoever.
While many Exchange people strongly believe that it is unsafe, they are never able to point to a definitive source (Microsoft) to justify. Usually it is, "somebody told me it was unsafe" or "I heard it was unsafe".
Greg/Microsoft MVP - Windows File Systems
Microsoft
