On Jun 25, 2008, at 12:53 PM, Darren Reed wrote: > eric kustarz wrote: >> >> On Jun 25, 2008, at 12:02 PM, Darren Reed wrote: >> >>> eric kustarz wrote: >>>> >>>> On Jun 25, 2008, at 11:49 AM, Darren Reed wrote: >>>> >>>>> This would seem to be a significant use case for the model of >>>>> having >>>>> non-overlapping data types in each of the two caches. Since no >>>>> reply >>>>> was received on zfs-discuss, I'm redirecting it to psarc to >>>>> indicate that >>>>> this question isn't closed. >>>> >>>> I see some comments, but no direct question. So what is the >>>> question? >>> >>> If the primary and secondary cache are different media, especially >>> in the case >>> of one being non-volatile, shouldn't it be possible to allow the >>> user to specify >>> that they want to use the non-volatile cache for meta data without >>> requiring >>> them to forgo caching user data in a volatile cache? >> >> Sure: >> # zfs set primarycache=all tank/fs >> # zfs set secondarycache=metadata tank/fs >> >> ARC (server memory) is the primary cache, l2ARC (SSD) is the >> secondary cache. >> >> eric > > Oh. are you saying that because metadata is directly s[ecofoed to be > cached in one place, it won't also be cached in the other? The case > didn't make that behaviour clear, if so.
No - the ARC will cache both data and metadata. The l2ARC will only cache metadata. > > > the desire would be primary=user data, secondary=meta data... Desire for what workload? You would have to *always* go to the secondary cache (or disk) for metadata in order to get to the data cached in the primary cache. I don't see a sensible use case for this - this is why we are not allowing a data only option. But we've been over this already. eric
