ZFS L2ARC hit ratio

[Wiktor Niesiobedzki]

2011/6/24 Attila Nagy <bra at fsn.hu>:
> On 06/21/11 21:59, Wiktor Niesiobedzki wrote:
>>
>> I've recently migrated my 8.2 box to recent stable:
>> FreeBSD kadlubek.vink.pl 8.2-STABLE FreeBSD 8.2-STABLE #22: Tue Jun  7
>> 03:43:29 CEST 2011     root at kadlubek:/usr/obj/usr/src/sys/KADLUB  i386
>>
>> And upgraded my ZFS/ZPOOL to newest versions. Though through my
>> monitoring I've noticed some declination in L2ARC hit ratio (server is
>> not busy, so it doesn't look that suspicious). I've made some tests
>> today and I guess, that there might be some problem:
>
> Likely because vfs.zfs.l2arc_noprefetch is now 1.
>
>

I'm running on i386 so prefetch for me was always disabled. It turns
out, that the "bad" behaviour is a result of putting:
vfs.zfs.prefetch_disable=0

In loader.conf

I thought that this is somehow better in ZFS v28, than in v15. Anyhow,
it looks like prefetching shall be left disabled for now.


Cheers,

Wiktor Niesiobedzki