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Date: Sun, 30 Dec 2012 18:25:01 -0500
From: Nikolai Lifanov <lifanov@mail.lifanov.com>
To: <kpaasial@gmail.com>
Subject: Re: Zpool made of =?UTF-8?Q?ZVOLs=3F?=
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> Is it possible and even recommended to create a zpool out of block
> devices that are actually ZVOLs?
>
> I'd like to have a separate zfs pool for poudriere because building
> ports with it disrupts the snapshotting on my main pool if the
> poudirere jails are created on it. At the same time I don't want to
> resort to using external disks to create a pool that is only used for
> a jail or two.
>
> Regards,
>
> -Kimmo
>

I'm sure that this is not what you want.
I think you are trying to snapshot your root pool and volatility + size 
of poudriere data makes this impractical. The first pool would still be 
the provider of zvols for the second pool.
If you can't have pools backed by separated devices (i.e. rpool on 
separate disks from tank), then you can always arrange the data that 
poudriere is interfering with to be on a different dataset.
So, from tank/poudriere/... arrangement you can move to tank/ROOT/... 
and tank/DATA/poudriere.

- Nikolai Lifanov