From owner-freebsd-fs@freebsd.org  Wed Dec 14 09:57:33 2016
Return-Path: <owner-freebsd-fs@freebsd.org>
Delivered-To: freebsd-fs@mailman.ysv.freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by mailman.ysv.freebsd.org (Postfix) with ESMTP id 1179BC76C0F
 for <freebsd-fs@mailman.ysv.freebsd.org>; Wed, 14 Dec 2016 09:57:33 +0000 (UTC)
 (envelope-from 000.fbsd@quip.cz)
Received: from elsa.codelab.cz (elsa.codelab.cz [94.124.105.4])
 (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
 (Client did not present a certificate)
 by mx1.freebsd.org (Postfix) with ESMTPS id C7F701C9F
 for <freebsd-fs@freebsd.org>; Wed, 14 Dec 2016 09:57:32 +0000 (UTC)
 (envelope-from 000.fbsd@quip.cz)
Received: from elsa.codelab.cz (localhost [127.0.0.1])
 by elsa.codelab.cz (Postfix) with ESMTP id 4395C28437;
 Wed, 14 Dec 2016 10:57:24 +0100 (CET)
Received: from illbsd.quip.test (ip-86-49-16-209.net.upcbroadband.cz
 [86.49.16.209])
 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))
 (No client certificate requested)
 by elsa.codelab.cz (Postfix) with ESMTPSA id A1E9128429;
 Wed, 14 Dec 2016 10:57:23 +0100 (CET)
Subject: Re: Re-sparse a file-backed IO device + zfs
To: Jan Bramkamp <crest@rlwinm.de>, freebsd-fs@freebsd.org
References: <fa5f1d106a6b4a21ad408b30e8b14ffa@exch2-4.slu.se>
 <43b81c7e-8a7b-73f4-0a13-5c91c92663b6@rlwinm.de>
From: Miroslav Lachman <000.fbsd@quip.cz>
Message-ID: <58511783.9000702@quip.cz>
Date: Wed, 14 Dec 2016 10:57:23 +0100
User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:42.0) Gecko/20100101
 Firefox/42.0 SeaMonkey/2.39
MIME-Version: 1.0
In-Reply-To: <43b81c7e-8a7b-73f4-0a13-5c91c92663b6@rlwinm.de>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 8bit
X-BeenThere: freebsd-fs@freebsd.org
X-Mailman-Version: 2.1.23
Precedence: list
List-Id: Filesystems <freebsd-fs.freebsd.org>
List-Unsubscribe: <https://lists.freebsd.org/mailman/options/freebsd-fs>,
 <mailto:freebsd-fs-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-fs/>
List-Post: <mailto:freebsd-fs@freebsd.org>
List-Help: <mailto:freebsd-fs-request@freebsd.org?subject=help>
List-Subscribe: <https://lists.freebsd.org/mailman/listinfo/freebsd-fs>,
 <mailto:freebsd-fs-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Wed, 14 Dec 2016 09:57:33 -0000

Jan Bramkamp wrote on 2016/12/13 10:59:
> On 13/12/2016 07:54, Karli Sjöberg wrote:

>> Wouldn't you have needed TRIM on the disk(s) inside the VM and it
>> would have taken care of all this for you?
>
> The ahci-hd driver supports TRIM on ZFS volumes. Why do you use sparse
> file instead of a ZFS volume?

I something had not changed you need twice the space of ZVOL to make a 
snapshot. So in some scenarios it is better to use files instead of ZVOL.

Miroslav Lachman