Examining cache needs for tempdb

Look at your use of tempdb:

With this information, you can a form a rough estimate of the amount of simultaneous I/O activity in tempdb. Depending on your other cache needs, you can choose to size tempdb so that virtually all tempdb activity takes place in cache, and few temporary tables are actually written to disk.

In most cases, the first 2MB of tempdb are stored on the master device, with additional space on another logical device. You can use sp_sysmon to check those devices to help determine physical I/O rates.