Nimbostratus
CirrusA very good article:
https://devcentral.f5.com/articles/-the101-irules-101-datagroups-amp-tables
An extract: "Whether you’re storing 100 or 100,000 entries, queries are roughly the same thanks to the indexed, hashed format of data groups. This makes them far and away the best option for storing large lists of data as well as frequently performed queries that can be represented in a read-only fashion. The bottom line is: If you’re not updating the data in the list, and you’re dealing with more than a handful of items, be it strings, IPs or otherwise, datagroups are likely your best bet."