From owner-freebsd-stable@FreeBSD.ORG Fri Feb 3 15:03:57 2012 Return-Path: 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 46720106564A for ; Fri, 3 Feb 2012 15:03:57 +0000 (UTC) (envelope-from petefrench@ingresso.co.uk) Received: from constantine.ingresso.co.uk (constantine.ingresso.co.uk [IPv6:2a02:b90:3002:e550::3]) by mx1.freebsd.org (Postfix) with ESMTP id D8F5A8FC15 for ; Fri, 3 Feb 2012 15:03:56 +0000 (UTC) Received: from dilbert.london-internal.ingresso.co.uk ([10.64.50.6] helo=dilbert.ingresso.co.uk) by constantine.ingresso.co.uk with esmtps (TLSv1:AES256-SHA:256) (Exim 4.76 (FreeBSD)) (envelope-from ) id 1RtKfv-0003ND-54; Fri, 03 Feb 2012 15:03:43 +0000 Received: from petefrench by dilbert.ingresso.co.uk with local (Exim 4.76 (FreeBSD)) (envelope-from ) id 1RtKfv-000BKF-4L; Fri, 03 Feb 2012 15:03:43 +0000 To: dmagda@ee.ryerson.ca, petefrench@ingresso.co.uk In-Reply-To: <015aa2883208e47457fdd56e63aab878.squirrel@webmail.ee.ryerson.ca> Message-Id: From: Pete French Date: Fri, 03 Feb 2012 15:03:43 +0000 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 List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 03 Feb 2012 15:03:57 -0000 > AFAIK, there is no way to specify the sector size to use in a ZFS pool: it > is completely automatic when you call "zpool create". Ideally it should > query the disk about its sector size and use that, but I don't know if > that has been implemented (and can't be bothered to dig through the source > at this time :). I think we are talking about different things - the sector size used by the zpool on the underlying system is automatic, and may or may not come from the disc sector size (like you, I hope it does, but havent checked ;-) ). 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 ? -pete.