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Date: Tue, 23 Sep 2014 09:26:44 -0600 (MDT)
From: Warren Block <wblock@wonkity.com>
To: Beeblebrox <zaphod@berentweb.com>
Subject: Re: Gpart: Adding mirror to existing zpool
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On Tue, 23 Sep 2014, Beeblebrox wrote:

> Hi.
> I have added another HDD to my system and I want to mirror my existing zpool
> named mydata on HDD1. I assume that both of the GPT partitions on either HDD
> housing mydata should be the same size, but I am a bit lost as to how to run
> gpart for this.
>
> # gpart add -a 4k -s <what?> -i 3 ada2

The output of 'gpart show' can be used to get the values from the 
existing drive.  But 'gpart backup' and 'gpart restore' are easier.

> Setting size parameter to output from "gpart show ada*1*p3", will not make
> both of these partitions properly synced IMHO. What would be the solution
> here?

Sorry, I don't understand this.  If the sizes of two partitions are 
identical, they can be used in a mirror.  Alignment is to make sure the 
drive performs well, particularly on writes.