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? Darren >> Darren J Moffat wrote: >>> Darren Reed wrote: >>> >>>> So I spent some time thinking about different directions you could >>>> build >>>> on this in the future, for example: >>>> 1) controlling the size of the ARC/L2ARC by controlling the cache size >>>> 2) specifying different backing storage for primary/secondary cache >>>> 3) having more than two levels of cache >>>> ...none of which is precluded by current efforts. >>>> >>>> With (2), if the backing storage for each cache is different and it >>>> is slower >>>> to access the secondary cache than the primary, then you may not want >>>> metadata to be stored in the secondary cache for performance reasons. >>>> >>>> As an example, you might be using NVRAM (be it flash or otherwise) >>>> for the primary cache and ordinary RAM for the secondary. In this >>>> case >>>> you probably don't want any metadata to be stored in the secondary >>>> cache (power failure issues) but the same may not hold for user data. >>>> But I'm probably wrong about that. >>>> >>> >>> I doubt you would be, the primarycache is system memory not a cache >>> device. The secondarycache is the L2ARC devices specified with the >>> "cache" vdev type to zpool so your examle would be the otherway around. >>> >>> >
