Vinum Offset for Swap: 265 or 281?

[Greg 'groggy' Lehey]

On Sunday, 19 October 2003 at  0:42:38 -0700, rtjohan at syspres.com wrote:
> Hi,
>
> Sanity check whether the mirrored vinum root drive is setup correctly.
> Going to setup two more machines the same way, so wanted to make sure the
> reference machine was setup correctly.
>
> Was surprised to see that the vinum dumpconfig shows the offset for the
> swap partition to be 265. Remember vaguely that it was supposed to be 281.
> Do I have a misconfigured machine? The bsdlabel reports the offset to be
> 281. The vinum.conf used driveoffset of 265s for swap - would think it
> should have been 281s.
>
> The machine works, but have had a couple of unexplained reboots. The
> mirrored drives are ad4s1 and ad8s1.

Vinum uses the first 265 sectors on a drive for configuration
information.  That has never changed.  It leaves the first 7 sectors
free for other stuff and puts the Vinum label in sector 8.
Unfortunately, this isn't compatible with bootstraps, which use
sectors 1 to 16.  The result is that if you put a Vinum drive exactly
at the beginning of a bootable disk, you will overwrite the bootstrap.
Thus the recommendation to put the drive at offset 16, so that nothing
will get clobbered.  This means that the first subdisk in the drive
will be at offset 281 from the beginning of the disk.  The offset of
the first subdisk in the drive remains the same at 265.  That's what
you have on your system:

>  b:   4194023      281      swap
>  h: 398283401       16     vinum

If you're having "reboots" (I suppose you mean panics or spontaneous
resets), it's almost certainly not because of the disk layout.  Follow
the instructions and we can probably find out what it is.  Note that
Vinum seems to be tickling bugs in -CURRENT ata code at the moment.

Greg
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