From owner-freebsd-hackers@FreeBSD.ORG Wed Jun 23 00:29:21 2004 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id D2DDF16A4CE for ; Wed, 23 Jun 2004 00:29:21 +0000 (GMT) Received: from web53302.mail.yahoo.com (web53302.mail.yahoo.com [206.190.39.231]) by mx1.FreeBSD.org (Postfix) with SMTP id 80D0343D4C for ; Wed, 23 Jun 2004 00:29:21 +0000 (GMT) (envelope-from non_secure@yahoo.com) Message-ID: <20040623002850.95962.qmail@web53302.mail.yahoo.com> Received: from [24.94.23.114] by web53302.mail.yahoo.com via HTTP; Tue, 22 Jun 2004 17:28:50 PDT Date: Tue, 22 Jun 2004 17:28:50 -0700 (PDT) From: Joe Schmoe To: freebsd-hackers@freebsd.org MIME-Version: 1.0 X-Mailman-Approved-At: Wed, 23 Jun 2004 12:06:57 +0000 Content-Type: text/plain; charset=us-ascii X-Content-Filtered-By: Mailman/MimeDel 2.1.1 Subject: A few technical items on UFS2 and snapshots... X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 23 Jun 2004 00:29:22 -0000 (posted to -questions a few days back, but with no response) Hi - a few questions about UFS2 and snapshots: 1. Is it dangerous to mount all 20 possible filesystem snapshots and _leave them mounted_ to use at any time ? What about automatically mounting all 20 snapshots at boot time ? 2. Related to the first question, it seems like I am getting space out of nowhere ... that is, if I fill up a drive, then make a snapshot, then erase the drive and fill it again, then make another snapshot ... and do this 20 times, AND THEN mount all 20 snapshots, it seems like I now have 20x as much disk space as before (granted, most of it is read-only) ... it seems like I am getting something for nothing. What am I missing here ? What tradeoffs do I begin to make as I mount up more and more snapshots and get more and more browsable space ? 3. When I mount a snapshot, as described in the man page, but then later mount -uw the snapshot ( to make that a writeable mount) and, say, touch a file or create a file in the mounted snapshot ... what exactly am I doing ? Have I corrupted the snapshot ? Is it still usable as a snapshot ? Where does this space end up being used at if I write a file in a write-enabled, mounted snapshot ? 4. This is not related to snapshots, but is a UFS2 question ... I see that if I am doing filesystem activity, and before I can sync the disks, my machine crashes ... the machine sort of goes back in time when it reboots - the files or directories I had created no longer exist when it reboots. This is expected, I suppose, and makes sense. However, it seems like I have also seen the following behavior: write file A write file B crash file A exists, but B does not write file B crash BOTH file A and B _no longer exist_ Is this possible ? Have I really seen that behavior, or am I remembering it wrong ? I swear that I have seen something like this happen ... if this is possible, can someone explain how ? It seems like it shouldn't be possible... Thanks! --------------------------------- Do you Yahoo!? Yahoo! Mail is new and improved - Check it out!