What is disk latency?

Disk latency refers to the time delay between a request for data and the return of the data. It sounds like a simple thing, but this time can be critical to the performance of a system.

What is a good disk latency?

For hard drives, an average latency somewhere between 10 to 20 ms is considered acceptable (20 ms is the upper limit). For solid state drives, depending on the workload it should never reach higher than 1-3 ms. In most cases, workloads will experience less than 1ms latency numbers.