From owner-freebsd-questions@FreeBSD.ORG Tue Mar 13 19:14:27 2007 Return-Path: X-Original-To: questions@freebsd.org Delivered-To: freebsd-questions@FreeBSD.ORG Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 96F0216A403 for ; Tue, 13 Mar 2007 19:14:27 +0000 (UTC) (envelope-from wmoran@potentialtech.com) Received: from mail.potentialtech.com (internet.potentialtech.com [66.167.251.6]) by mx1.freebsd.org (Postfix) with ESMTP id 5A12713C455 for ; Tue, 13 Mar 2007 19:14:27 +0000 (UTC) (envelope-from wmoran@potentialtech.com) Received: from vanquish.pgh.priv.collaborativefusion.com (pr40.pitbpa0.pub.collaborativefusion.com [206.210.89.202]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mail.potentialtech.com (Postfix) with ESMTP id 5D331EBC6A; Tue, 13 Mar 2007 15:14:26 -0400 (EDT) Date: Tue, 13 Mar 2007 15:14:25 -0400 From: Bill Moran To: "Pietro Cerutti" Message-Id: <20070313151425.5fc464db.wmoran@potentialtech.com> In-Reply-To: References: <64784.69.129.174.18.1173797935.squirrel@email.polands.org> <20070313111029.49bd1d14.wmoran@potentialtech.com> <53038.69.129.174.18.1173799128.squirrel@email.polands.org> <20070313143555.ee27a265.wmoran@potentialtech.com> X-Mailer: Sylpheed 2.3.1 (GTK+ 2.10.9; i386-portbld-freebsd6.1) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: questions@freebsd.org Subject: Re: UFS2 Snapshot limitiations X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 13 Mar 2007 19:14:27 -0000 In response to "Pietro Cerutti" : > On 3/13/07, Bill Moran wrote: > > In response to "Pietro Cerutti" : > > > > > On 3/13/07, Doug Poland wrote: > > > > > > > > On Tue, March 13, 2007 10:10, Bill Moran wrote: > > > > > In response to "Doug Poland" : > > > > > > > > > >> Hello, > > > > >> > > > > >> I seem to recall, but cannot find, the limitation on the number of > > > > >> snapshots allowed on UFS2. Could someone point me in the right > > > > >> direction please? > > > > > > > > > > The handbook has it: > > > > > http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/snapshots.html > > > > > > > > > Thank you very much. > > > > > > > > > > Sorry for joining the thread, but it's raised my curiosity: what's the > > > reason for this limit? > > > > I'm not 100% sure, but I believe it's because snapshot information is stored > > in the filesystem superblock, and that's all that can fit in the space > > available in the superblock. > > This is the same thing that came to my mind, but in the handbook page I found: > "Active snapshots are recorded in the superblock so they are > persistent across unmount and remount operations along with system > reboots." > > 1) what an "active" snapshot is? I think you're trying too hard to read into this. Active snapshot, as opposed to a snapshot that has been deleted/unmounted and existed in the past, is what I took it to mean. Keep in mind that the existence of a snapshot mandates certain activity on the part of the FFS drivers in order to keep that snapshot's data valid. Thus, any snapshot is "active" as long as it exists. In other words, if you delete a file from the filesystem while a snapshot is active, the FFS drivers can not reclaim that space, as it would result in data loss within the snapshot. > 2) is that limit limited (...) to active snapshots? Sure. I don't know what an "inactive" snapshot would be. -- Bill Moran http://www.potentialtech.com