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Date:      Thu, 26 Jan 2012 16:49:23 -0700
From:      "Kenneth D. Merry" <ken@freebsd.org>
To:        Nikolay Denev <ndenev@gmail.com>
Cc:        freebsd-fs@freebsd.org
Subject:   Re: BIO_DELETE support for ZVOLs?
Message-ID:  <20120126234923.GA712@nargothrond.kdm.org>
In-Reply-To: <B2F72C4D-6B95-4801-8865-D40E6FA92726@gmail.com>
References:  <B2F72C4D-6B95-4801-8865-D40E6FA92726@gmail.com>

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On Wed, Jan 25, 2012 at 09:51:04 +0200, Nikolay Denev wrote:
> I'm don't know if anyone thought about this but it seems like a
> nice feature to support TRIM like functionality for ZVOLs.
> 
> For example : if there is a sparse ZFS volume, formatted with UFS,
> and you fill it up once, then the disk space used will be with the size of the ZVOL.
> Then even if there is freed space on the UFS filesystem,
> the ZVOL disk space allocated from the ZVOL will remain the same.
> 
> This also will be very nice if can be supported for FC exported ZVOLs via the new CAM Target Layer.
> 

We're (i.e. Spectra Logic) planning to do trim support for CTL.  The
eventual goal is to plumb it all the way down through ZFS via the file
and ZVOL paths, so that ZFS frees the space, and passes the trim commands
down to any component disks so they can free the blocks as well.

I don't know when that'll all get done, but we're planning to do it.  If
anyone wants it sooner, they're welcome to help with the implementation. :)

Ken
-- 
Kenneth Merry
ken@FreeBSD.org



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