Zaphod Beeblebrox zbeeble at gmail.com
Mon Sep 29 15:09:47 UTC 2008

On Mon, Sep 29, 2008 at 3:16 AM, Andrew Snow <andrew at modulus.org> wrote:

> However, as a core general purpose filesystem, it seems to have flaws, not
>> the least of which is a re-separation of file cache and memory cache.
> For me, this doesn't matter because ZFS is so much faster than UFS
> overall.  Even if you don't use any of its features, the latest version
> does sequential I/O and heavy random I/O faster than UFS on the same
> hardware for me.
> Cases where UFS is faster are proving to be the exception rather than
> the rule.
> However, I cannot recommend its use until it is stable, which it
> currently still is not, under very heavy load.

I certainly can't agree with this.  I don't think you're measuring the
performance of the machine --- only measuring the performance of the
filesystem.  When ZFS is active, memory is committed in the kernel to ZFS.
That memory is then no longer available for paging.  Also, there exists data
within the ARC (I'm always tempted to say the ARC Cache, but that is
redundant) that is also then in paging memory.  You end up having to tune
the size of the ARC to your workload, which is how UN*X did it upto 1992 or
so.  If you choose the wrong size for the ARC, you end up with very poor

In particular, the ARC fights for space with the nvidia binary driver (which
really does need _real_ memory).  To have the driver work at all, I have to
keep the ARC from growing too large --- which is at odds with filesystem

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