l2arc - why not attempt to make it persistent?

devsk devsku at gmail.com
Sun May 22 11:30:51 EDT 2011


Are u using it for metadata only or for all?

-devsk

On May 22, 8:05 am, Uncle Stoatwarbler <stoatw... at gmail.com> wrote:
> Given that:
>
> 1: If there is a cache device problem the cache device gets dumped.
> 2: If there is a cache object inconsistency with what's on disk then the
> cached objects get dumped.
> 3: if there are any other kinds of inconsistencies then the disk wins
>
> Why not attempt to preserve the l2arc cache across reboots/mounts and as
> an effect, (hopefully) speed up access from the outset rather than
> having to wait for the cache to build out again? (if there are any
> problems, the cache should be dumped, but if it's intact, why dump it?)
>
> I've just been benchmarking my (rather slow, cheap) ssds vs disks and
> even for the worst case scenarios there are 5-10 times the speed of the
> spinning media for all except sequential writes (where they are only
> twice the speed)
>
> My concern partly stems from the limited write cycles of ssds
> (especially cheap ones) and having just seen 40Gb of cache (on a 64Gb
> cache device) being dumped, but also from the realization that my system
> is significantly slower after a reboot, until the cache is repopulated
> (zfs on root)
>
> Alan



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