Date: Tue, 22 Jun 2004 17:28:50 -0700 (PDT) From: Joe Schmoe <non_secure@yahoo.com> To: freebsd-hackers@freebsd.org Subject: A few technical items on UFS2 and snapshots... Message-ID: <20040623002850.95962.qmail@web53302.mail.yahoo.com>
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(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!
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