Evaluating cache needs

Generally, configure caches in proportion to the number of times that the pages in the caches will be accessed by queries, and configure pools within caches in proportion to the number of pages used by queries that choose I/O of that pool’s size.

If your databases and their logs are on separate logical devices, you can estimate cache proportions using sp_sysmon or operating system commands to examine physical I/O by device.

See Performance and Tuning Series: Monitoring Adaptive Server with sp_sysmon.