gmirror is confusing me, will I be bitten by the last-sector-use?

illoai at gmail.com illoai at gmail.com
Tue Feb 21 16:50:30 PST 2006


> > Now, how can I check whether my current partitions will cause trouble
> > with the metadata-sector or not? I've done some searching on the net,
> > but I'm still a bit confused. If I understand correctly, the consumers
> > ad0/ad2 span 488397168 sectors (mediasize/sectorsize), and the
> > mirror/gm0 spans 488397167 sectors.
> >
> In short: kernel (g_mirror) won't let you write to the last sector of its
> media.
>

So long as your partition(s) exist(s) within the mirror device, you can't
problem the metadata.  If you tried writing to the last sectors of /dev/ad0
or /dev/ad2, you would damage or destroy the metadata.  So, don't do that.

I am curious about this case, does FreeBSD periodically check for the
existance of the metadata, or (like some things, the kernel for instance)
does it, once read and not rewritten, exist in memory, thus being able
to be written over on disk, not to be noticed until reboot (or modification,
if such would be your wont)?

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