Seems like an simple question, but using Resource monitor and Performance monitor, I only seem to get snapshots of memory usage.
What is the best way to determine what available memory was at 03:00 hours yesterday? Is it possible to do with the built-in perfomance software of windows server?
You can't do it retrospectively unless you've already created a working counter log but if you want to do this in the future then just create a counter log in perfmon.
If this is a long term requirement you might consider using something like MRTG to gather, record and chart the data from your Windows server(s). This way you can gather the data over extended periods easily.
What is the best way to determine what available memory was at 03:00 hours yesterday?
Unless you were already logging it, you can't. That information is only recorded if you record it. So now that the time has passed, you can't get that information back. To enable you to have it in the future, look into what either Chopper or John suggested.
You might also want to think about a monitoring system that can record this kind of information for all your servers... they're generally pretty complicated to set up, but well worth the effort, because you can make sure you'll always have an answer to this kind of question.
