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Date:      Wed, 18 Jan 2006 14:18:31 -0500
From:      Kris Kennaway <kris@obsecurity.org>
To:        Ensel Sharon <user@dhp.com>
Cc:        freebsd-hackers@freebsd.org
Subject:   Re: tuning to run large (1000+) numbers of null_mounts
Message-ID:  <20060118191831.GA47747@xor.obsecurity.org>
In-Reply-To: <Pine.LNX.4.21.0601181228590.8684-100000@shell.dhp.com>
References:  <Pine.LNX.4.21.0601181228590.8684-100000@shell.dhp.com>

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On Wed, Jan 18, 2006 at 12:35:29PM -0500, Ensel Sharon wrote:
>=20
> I am running over 2000 null mounts on a FreeBSD 6.0-RELEASE system.  I am
> well aware of the status of the null_mount code, as advertised in the
> mount_nullfs man page:
>=20
>      THIS FILE SYSTEM TYPE IS NOT YET FULLY SUPPORTED (READ: IT DOESN'T
> WORK)
>      AND USING IT MAY, IN FACT, DESTROY DATA ON YOUR SYSTEM.  USE AT YOUR
> OWN
>      RISK.  BEWARE OF DOG.  SLIPPERY WHEN WET.
>=20
> So, based on this, all of my null_mounts are actually mounted read-only.

As others have said, this is no longer applicable to FreeBSD 6.0, and
it's been removed from HEAD.

> I am noticing both system instability and data corruption issues on disk
> following crashes.  Both of these seem to be related to the null
> mounts.  I have two very quick questions:

I've not used 2000 null mounts, but I commonly use ~100 of them at
once on a number of systems and have not observed problems relating to
this.  However, it's possible you're finding new bugs, so you should
report them in the usual way (gdb backtrace of panics, etc).

Kris

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