Some questions about vfs.zfs.prefetch_disable=1 and ZFS filesystem versions

Jeremy Chadwick freebsd at jdc.parodius.com
Tue Mar 16 05:11:50 UTC 2010


On Tue, Mar 16, 2010 at 01:40:25AM +0200, Dan Naumov wrote:
> After looking at the arc_summary.pl script (found at
> http://jhell.googlecode.com/files/arc_summary.pl), I have realized
> that my system has set vfs.zfs.prefetch_disable=1 by default, looking
> at dmesg, I see:
> 
> =========================
> ZFS NOTICE: Prefetch is disabled by default if less than 4GB of RAM is present;
>             to enable, add "vfs.zfs.prefetch_disable=0" to /boot/loader.conf.
> =========================
> 
> ...except I do have 4gb of RAM. Is this caused by integrated GPU
> snatching some of my memory at boot? From dmesg:
> 
> =========================
> real memory  = 4294967296 (4096 MB)
> avail memory = 4088082432 (3898 MB)
> =========================

I've blogged about this problem when testing out 8.0-RC1.  See the
bottom third of my post for an explanation:

http://koitsu.wordpress.com/2009/10/12/testing-out-freebsd-8-0-rc1/

The message is confusing/badly worded, despite having gone through
numerous commits to change its wording.

-- 
| Jeremy Chadwick                                   jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |



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