ZFS cache hierarchy controls
An interesting new feature had it´s flag day. With PSARC 2008/393 a feature called “zfs primarycache and secondarycache prop” found it´s way into Solaris for build 96. With this properties you can control, what ZFS caches in the ARC and the L2ARC.
The introduction of the 'primarycache' property will allow administrators the ability to control what is cached in the ARC. The possible choices are: all, none, and metadata. If 'all' is chosen, then both user data and metadata are cached. If 'none' is chosen, then neither user data nor metadata is cached. If 'metadata' is chosen, then only metadata is cached. The default is 'all'. The introduction of the 'secondarycache' property will allow administrators the ability to control what is cached in the l2ARC. The possible choices are the exact same as 'primarycache'. The default is also 'all'.
This is interesting for situations, when you know that your application is caching data as well (thus it makes no sense to cache it twice) or you aware of the fact that caching is just waste of time because of the access pattern. You can find details about this feature in the PSARC discussion for 2008/393 and in the specs.