As Gail suggested above, the higher is this ratio the better. It simply means that your memory is having sufficient amount of data in the cache which will reduce the physical I\O operations.

However, if you are really interested to go deeper into this analysis, create your small warehouse for analysis of memory,disk and cpu counters over the period of time(say 2 weeks) so that you can have a fair bit of idea on the overall processing. you may use DMVs or the good old perfmon but make sure that during this period you do not reboot sql server or use dbcc commands to flush the cache because logically it will impact the analysis negatively.

Thanks

Chandan