To make the window as large as possible there are some tricks you can try:
- Filter out junk data. In many TACACS+ Admin logs up to 90% of rows can be full of scripted commands from (amongst others) CiscoWorks. By setting up a pre-filter (Options/Import Options/Pre-Filter) you can filter out rows containing strings such as "Scripts", "ping" or "show". This can drastically increase the reporting window as matching rows are simply discarded during import.
- Use Multi-DB (new in v2.2). Depending on your deployment it may be possible to split your data and import each dataset into its own aaa-reports! backend database (or multi-db). For example, you have 2 ACS servers - one handling VPN and the other Device Admin. This is a prime candiate for 2 multi-dbs. Multi-Db can be enabled via the Options page.
The next major release, aaa-reports! enterprise edition, will feature an entirely new backend database engine with approximately 32GB of storage. Combined with Multi-DB and that's a HUGE potential.