Crystal Disk Mark and SQL Server recommended some benchmarking tools for SQL Server users via Glenn Berry’s SQL Server Performance Blog. Problem is, one of the tools is pretty badly flawed.

Berry recommended Crystal Disk Mark, which is a cute tool that ostensibly measures disk performance. Thing is, it does a pretty shoddy job. If you run the test, you’ll notice that the disk queue for the drive its testing is never deeper than one. That is, it doesn’t do multi-threaded or overlapped I/O requests. Instead, it issues a single blocking requests. It doesn’t take long to download the source code and confirm this fact.

For desktop machines, doing only one I/O at a time isn’t so bad because that matches the workload desktop machines typically show their drives during normal use.

It seems a bit irresponsible to recommend such a tool for servers, though–particularly machines which will be running SQL Server, where multiple outstanding I/O operations are key to achieving any sensible level of performance. I like to have at least a couple outstanding I/O operations per logical spindle on the servers I run. This lets the controller and the drive have a shot at elevator seeking across multiple requests, combining redundant requests in cache, and batching as best as possible.

Since none of Crystal Disk Mark’s test modes provide any I/O request depth, it won’t provide an accurate measure of performance for the disk arrays and storage subsystems that are typically used with SQL Server installations and it isn’t an appropriate tool for capacity planning or evaluating hardware for such installations.







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