gmirror, gpart and MBR vs GPT in the Handbook

Warren Block wblock at
Mon Dec 2 15:56:15 UTC 2013

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 

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.

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