eric kustarz wrote: > > 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.
Ugh, brain fade... I was thinking of the caches as being in parallel rather than layered. Darren
