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Volume Shadow Copy For Linux?
An anonymous reader writes "I was asked to manage a number of Linux servers at work. I would like to use volume snapshots to improve my backup scripts and keep recent copies of data around for quick restore. I normally manage Windows servers and on those I would just use Microsoft's Volume Shadow Copy for this. I tried Linux LVM snapshots, but most of the servers I manage run regular partitions with ext3 file systems, so LVM snapshots will not work. I found some versioning file systems out there like ext3cow and Tux3. Those look interesting, but I need something I can use on my existing ext3 file systems. I also found the R1Soft Hot Copy command-line utility, but it does not yet support my older 2.4 Linux servers. What are you using to make snapshots on Linux?"
If you have backups, then moving to LVM is obviously the way to go if you desire snapshots. The others options are short-term hackery, LVM was designed from the ground up to do such things. And Ext3 has nothing to do with the price of butter.
To clarify, let me rephrase your question for the other way around
"I was asked to manage a number of *Windows* servers at work. I would like to use volume snapshots to improve my backup scripts and keep recent copies of data around for quick restore. I tried Windows Shadow Copy, but most of the servers I manage run MBR partitions with FAT file systems, so Shadow Copy will not work. I found some versioning file systems out there... Those look interesting, but I need something I can use on my existing FAT file systems. I also found --random freeware--, but it does not yet support my older Windows NT 3.5 servers. What are you using to make snapshots on Windows?"
Except, in that case, it makes more sense because the filesystem is the determining factor, not the volume management. If you have LVM, it doesn't matter what the underlying filesystem is, really. Stop faffing about - if you have a server, with backups, that you need snapshots on, take the hit and wipe the drives to a config that supports that... while you're there upgrade that damn kernel already. If nothing else, it will test that the backups you're making are actually worth the effort. It's like complaining that 95 on FAT16 doesn't support Shadow Copy. If you absolutely *can't* take those servers down, or am unable to restore your backups to another machine for testing such changes (whether because of compatibility, software licensing and/or bad backups), you have bigger problems than some random desire for a feature you don't actually *need* at the moment.
If they are indeed regular partitions, he can't use LVM snapshots. However, the best solution is to convert from partitions to LVM volumes. It's a little effort to do so, but switching is worth it. Second best is to wait until btrfs is more usable. As a ZFS user, I can say that filesystem-level snapshot are much nicer than LVM snapshots in lots of ways.
Another possibility is to abuse hardlinks. You can create a copy of a directory with cp -al, and then overwrite (not modify) files on the original, you'd have copy-on-write copy. If you make your backups with rsync, you can configure rsync to never write to existing files and always overwrite, then use cp -al each weak or day, to store "incremental" backups for weeks and maybe more. I personally found this solution nice, but then I installed Solaris on the backup machine and used ZFS snapshots which do the same safer, simpler and more efficiently. If the backups are stored on a separate machine, switching it to Solaris is an option.
Another thing that can be done is to keep the LVM snapshots on a separate machine, and leave the current partitions as they are. It can be done with rsync, or a drdb device can be used to sync with the server (it can be created without reformatting the partitions, but you still need to make some changes like shrinking and/or moving the data, which might destroy the data if you don't know what you're doing).