From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from rx0ar-terminal-systems-international.ed.BIGPIPEINC.COM ([208.118.95.38]:50884 "EHLO mail.terminalsystems.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750943AbaLEShr (ORCPT ); Fri, 5 Dec 2014 13:37:47 -0500 Received: from localhost (localhost [127.0.0.1]) by mail.terminalsystems.com (Postfix) with ESMTP id 49FAB40671 for ; Fri, 5 Dec 2014 12:27:51 -0600 (CST) Received: from mail.terminalsystems.com ([127.0.0.1]) by localhost (tsiblade9.terminalsystems.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id bEpSeYygFq2F for ; Fri, 5 Dec 2014 12:27:45 -0600 (CST) Received: from [192.168.7.202] (unknown [192.168.7.202]) (using TLSv1 with cipher ECDHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) (Authenticated sender: jwest) by mail.terminalsystems.com (Postfix) with ESMTPSA id BA41B40670 for ; Fri, 5 Dec 2014 12:27:45 -0600 (CST) Message-ID: <5481F91B.6090700@terminalsystems.com> Date: Fri, 05 Dec 2014 12:27:39 -0600 From: James West MIME-Version: 1.0 To: linux-btrfs@vger.kernel.org Subject: Possibility to have a "transient" snapshot? Content-Type: text/plain; charset=ISO-8859-1; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: This is just a random idea that popped through my mind while I was looking into hardening a filesystem against damage, might be impractical, but the idea seems promising, and well suited to a snapshot file system. I'm sure some creative shell scripting could do something like this already, but I was more looking for something more bulletproof. General idea would be to have a transient snapshot (optional quota support possibility here) on top of a base snapshot (possibly readonly). On system start/restart (whether clean or dirty), the transient snapshot would be flushed, and the system would restart the snapshot, basically restarting from the base snapshot. If desired, the transient snapshot could be promoted to a regular snapshot (say after a software upgrade). If desired, a different base snapshot could be selected (although I'm sure the file system would have to be restarted to do this) From a caching perspective, this could make a noticable performance difference, since if you're running in a transient snapshot, the file system can be _extremely_ lazy about committing changes to disk. For the optional quote support I mentioned, on an unattended box, if the quota gets exceeded, a system reboot would probably fully correct the system. (Presumably a log file got out of control in that situation).