gmirror, gpart and MBR vs GPT in the Handbook

Julien Cigar jcigar at
Tue Dec 3 09:26:11 UTC 2013

On Mon, Dec 02, 2013 at 08:56:13AM -0700, Warren Block wrote:
> On Mon, 2 Dec 2013, Julien Cigar wrote:
> > If you want to use GPT with gmirror you may want to mirror each
> > partition instead of the whole disk.
> >
> > For example on my box I have the following:
> There are a couple of potential problems with that.  The big one is when 
> a disk fails and is replaced.  If you're not careful, the rebuild of all 
> those mirrored partitions will start at the same time.  Head contention 
> will bring that to a near-standstill.  It also puts a heavy load on the 
> drive that still works.  Hopefully it is not the same model and age as 
> the one that failed, or its "warranty timer" may also be close to 
> expiring.

That's true, I turned off autosynchronization of stale components to
avoid this kind of bad scenario ..

> A less-serious problem is that only the partitions are mirrored.  That 
> leaves out metadata like the partition tables and bootcode, but those 
> typically do not change very often and might not be a problem.  The 
> admin has to remember to manually install such things on a new 
> replacement disk, though.

It's just a matter of gpart backup / gpart restore, right ?

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