Date: Sat, 30 Mar 2002 23:01:04 -0500 From: Garance A Drosihn <drosih@rpi.edu> To: Kirk McKusick <mckusick@beastie.mckusick.com> Cc: arch@FreeBSD.ORG Subject: Re: UFS snapshots in current Message-ID: <p05101534b8cc3050bcdc@[128.113.24.47]> In-Reply-To: <200203282250.g2SMoDD99826@beastie.mckusick.com> References: <200203282250.g2SMoDD99826@beastie.mckusick.com>
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At 2:50 PM -0800 3/28/02, Kirk McKusick wrote: > From: Garance A Drosihn <drosih@rpi.edu> > > More useful question: what should I look at for > info on using snapshots? > >General references are found at: > > http://www.mckusick.com/softdep/index.html > >The soft updates paper has a section on snapshots. The >background fsck paper goes into snapshots (and their >general usage) in a bit more detail, so is likely to >be more useful. Okay, well, I was trying this out and I had something odd happen. As I sit here waiting for my PC to return to life, I'll ask if what I was trying to do something which would be a BadIdea(tm). I wanted to use a snapshot to "freeze" the system in time before doing a large-scale set of changes. So, I created a snapshot of /usr. I then did a 'cvs update' of /usr/src, and checked how the snapshot worked. It seemed to be doing just exactly what I wanted. I then got interrupted and forgot about the snapshot. I may have also done a reboot, but I'm not sure about that. Days pass, I come back, do another 'cvs update' of the latest sources. I buildworld, buildkernel, installkernel. So far no problem (note that /usr/obj is on a separate partition). I reboot, and go to do an installworld. It goes merrily along for awhile, and then just stops. After letting it sit there for about 15 minutes, I attention out of the buildworld. It had not used a lot of cpu time. so, I tried it again. it went a few lines and then stopped again. I finally decided to just reboot. The shutdown started, and then got stuck at 'Writing entropy file'. I then hit the power button. It didn't power off! I had to unplug the machine to get it to reboot. After it came back up, I removed the checkpoint file. I forget how large it was, but it was pretty large. Before removing it, I did a 'df -k -i', and /usr had plenty of spare filespace and spare inodes. I didn't know what else I should check for. By then the system told me that I had to do an fsck of /usr by hand, so I've done that, and now have 1500 files in lost+found. It happens I have an exact duplicate of my current system in a different set of partitions, so one way or another I can get the system back to what I need. But the main question is: Could my problems have been due to that snapshot being active when I did the 'installworld'? I only *meant* it to be there during the 'cvs update', buildworld, and buildkernel, but I had forgotten it was there. It's hard to believe that this was due to any of the changes made to current in the past week. And if it is a bad idea, how hard would it be to get it to fail a little more gracefully? :-) Also, if this had worked, I probably would have duplicated this new system to my backup partitions. From what I've read of the paper, I think that would not cause a problem (other than maybe wasting disk space), because a plain copy (using pax) wouldn't add the snapshot file to the list of snapshots in the superblock of the destination partition. True? -- Garance Alistair Drosehn = gad@eclipse.acs.rpi.edu Senior Systems Programmer or gad@freebsd.org Rensselaer Polytechnic Institute or drosih@rpi.edu To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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