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Date: Sun, 2 Jun 2013 15:27:03 -0600 (MDT)
From: Warren Block <wblock@wonkity.com>
To: Dmitry Morozovsky <marck@rinet.ru>
Subject: Re: Corrupt GPT header on disk from twa array - fixable?
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On Mon, 3 Jun 2013, Dmitry Morozovsky wrote:

> On Sun, 2 Jun 2013, Warren Block wrote:
>
> [snip]
>
>> gmirror is good.  GPT is also good.  The combination is a problem. gmirror
>> metadata overwrites the backup GPT, so those disks will show "corrupt" also.
>> For now, the recommended workaround is to just use MBR, which doesn't have any
>> metadata at the end of the disk.
>
> ... or gmirror not whole disks, but GPT partitions (as OP does, as far as I can
> tell from gmirror dmesg reports)

That works, but if there is more than one partition per disk, rebuilds 
fight with each other for the heads.