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Date:      Wed, 9 Mar 2011 13:28:50 +0000
From:      Tom Evans <tevans.uk@googlemail.com>
To:        Jeremy Chadwick <freebsd@jdc.parodius.com>
Cc:        Matthias Andree <matthias.andree@gmx.de>, freebsd-stable@freebsd.org
Subject:   Re: ZFS performance as the FS fills up?
Message-ID:  <AANLkTimMct3Ni0p7CBsmNJmW_t6e75mZcHhQ8dppQbCb@mail.gmail.com>
In-Reply-To: <20110309125132.GB62338@icarus.home.lan>
References:  <BD2C8439-AC1E-49CB-ABE2-9F7F0B292933@punkt.de> <20110308114810.GA37554@icarus.home.lan> <4D775CF1.1010501@gmx.de> <20110309125132.GB62338@icarus.home.lan>

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On Wed, Mar 9, 2011 at 12:51 PM, Jeremy Chadwick
<freebsd@jdc.parodius.com> wrote:
>
> Otherwise, I can imagine that prefetching could cause what you describe,
> which is enabled by default in 8.0 and 8.1 and auto-disables in 8.2 if
> the amount of available memory is less than 4GB.
>

I don't think this is accurate. Prefetch was certainly disabled by
default on 8.0 if you had 4GB of RAM or less, requiring the sysctl
vfs.zfs.prefetch_disable=0 to be set if you wanted prefetch and had
4GB of RAM or less.

Cheers

Tom



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