From owner-freebsd-stable@FreeBSD.ORG  Fri Feb  3 15:47:26 2012
Return-Path: <owner-freebsd-stable@FreeBSD.ORG>
Delivered-To: freebsd-stable@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 9DD441065670
	for <freebsd-stable@freebsd.org>; Fri,  3 Feb 2012 15:47:26 +0000 (UTC)
	(envelope-from dmagda@ee.ryerson.ca)
Received: from eccles.ee.ryerson.ca (eccles.ee.ryerson.ca [141.117.1.2])
	by mx1.freebsd.org (Postfix) with ESMTP id 59BCC8FC08
	for <freebsd-stable@freebsd.org>; Fri,  3 Feb 2012 15:47:26 +0000 (UTC)
Received: from webmail.ee.ryerson.ca (eccles [172.16.1.2])
	by eccles.ee.ryerson.ca (8.14.4/8.14.4) with ESMTP id q13FlLG1033270;
	Fri, 3 Feb 2012 10:47:21 -0500 (EST)
	(envelope-from dmagda@ee.ryerson.ca)
Received: from 206.108.127.2 (SquirrelMail authenticated user dmagda)
	by webmail.ee.ryerson.ca with HTTP; Fri, 3 Feb 2012 10:47:21 -0500
Message-ID: <01775b9823b5bacb14d03315a6321d61.squirrel@webmail.ee.ryerson.ca>
In-Reply-To: <E1RtKfv-000BKF-4L@dilbert.ingresso.co.uk>
References: <E1RtKfv-000BKF-4L@dilbert.ingresso.co.uk>
Date: Fri, 3 Feb 2012 10:47:21 -0500
From: "David Magda" <dmagda@ee.ryerson.ca>
To: "Pete French" <petefrench@ingresso.co.uk>
User-Agent: SquirrelMail/1.4.20
MIME-Version: 1.0
Content-Type: text/plain;charset=iso-8859-1
Content-Transfer-Encoding: 8bit
Cc: freebsd-stable@freebsd.org
Subject: Re: Sector size of a zvol
X-BeenThere: freebsd-stable@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Production branch of FreeBSD source code <freebsd-stable.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-stable>, 
	<mailto:freebsd-stable-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-stable>
List-Post: <mailto:freebsd-stable@freebsd.org>
List-Help: <mailto:freebsd-stable-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-stable>,
	<mailto:freebsd-stable-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 03 Feb 2012 15:47:26 -0000

On Fri, February 3, 2012 10:03, Pete French wrote:
> [...] But what I am talking about is the sector size
> presneted by the 'fake' disc that a ZVOL creates - that always seems
> to be 512 bytes, despite the fact that the zvol blocksize is 8k. Seems
> odd to me (and that 8k size os alterable, but just doesnt seem to
> be reflected in the zvol). As it stands I can make a zpool on top
> of 4k discs, a ZVOL using 8k blocks on top of that, but the things
> talking to it will use 512 byte chunks, which surely impacts performance ?

Try the following from the zfs(1M) man page:

    zfs create [-ps] [-b blocksize] [-o property=value] ... -V size volume
    [...]
	 -b blocksize

	   Equivalent to -o  volblocksize=blocksize.  If  this  option  is
	   specified  in  conjunction  with -o volblocksize, the resulting
	   behavior is undefined.

http://www.freebsd.org/cgi/man.cgi?query=zfs

Did use "blocksize" or "volblocksize" in your "zfs create" command?


A thread for zfs-discus on "volblocksize":

http://mail.opensolaris.org/pipermail/zfs-discuss/2005-November/000450.html