eric kustarz wrote: > > On Jun 23, 2008, at 1:20 PM, Darren Reed wrote: > >> eric kustarz wrote: >>> >>> On Jun 23, 2008, at 1:07 PM, Darren Reed wrote: >>> >>>> Tim Haley wrote: >>>>> .... >>>>> primarycache=all | none | metadata >>>>> >>>>> Controls what is cached in the primary cache (ARC). If set to >>>>> "all", then both user data and metadata is cached. If set to >>>>> "none", then neither user data nor metadata is cached. If set to >>>>> "metadata", then only metadata is cached. The default >>>>> behavior is >>>>> "all". >>>>> >>>> >>>> The description above kind of implies that user data is somehow >>>> separate to metadata >>>> but it isn't possible to say cache only user data (with the text >>>> given.) Is this just an >>>> oversight or is this really saying you cannot cache only the user >>>> data? >>> >>> We couldn't come up with any realistic workload that would want to >>> cache user data but not metadata, so we're not allowing it. >>> >>> We can always add the option later, but if someone has a realistic >>> use case for it, i'd be happy to add it now. >> >> It's not so much the "why", but maybe I'd like to say the primarycache >> gets metadata and the secondary cache gets user data (or vice versa.) >> If that make sense? Or would that require linkage between metadata >> and user data (across cache boundaries) in order to maintain sanity? > > It is the "why". If there's no reason to do it, then we shouldn't > allow it (adds more complexity, more confusion, more ways for a > customer to shoot themselves in the foot). > > However, if there is a legitimate use case, let's discuss that.
I think we can move that discussion to one of the ZFS discussion forums on OpenSolaris.org. The important point I was curious about was if there was an architectural ommission or mistake. Darren
