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Date:      Sun, 26 Jun 2011 23:35:34 +0200
From:      Wiktor Niesiobedzki <bsd@vink.pl>
To:        freebsd-fs@freebsd.org
Subject:   Re: ZFS L2ARC hit ratio
Message-ID:  <BANLkTi=G_W3V-M5_M3Vue%2BgYaA3TTHVwzQ@mail.gmail.com>
In-Reply-To: <4E0435B6.30004@fsn.hu>
References:  <BANLkTinyveD7D=PYv3eqdxZb=KneKxg9Zg@mail.gmail.com> <4E0435B6.30004@fsn.hu>

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2011/6/24 Attila Nagy <bra@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@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


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