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backing up active filesystems safely

Posted on 1998-08-04
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Last Modified: 2013-11-15
I'm using Redhat Linux 5.0 with a scsi 4mm tape drive.
I don't have any problems writing to or reading from the tape.
For example:
  To backup I can type:  tar -czvSf /dev/tape /home/mag
  To restore I can type:  cat /dev/tape >foo.tar.gz
    then I can type: gzip -d foo.tar.gz
    then I can type: tar xvf foo.tar
    and I'm back in business.

I have heard that tar is not a good backup tool to use if the filesystem is changing.

Is it any part of the filesystem that corrupts the backup?  Or is it only a problem if the file being backed up changes?

Is their a failsafe method of backing up the files to a tape drive?  dump?  zip?
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Question by:mag062397
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by:JYoungman
ID: 1637706
If the data being backed up changes during the backup,
you may find that the data on the tape for a given file does not correspond to what was the contents of the file at *any* time; it may be half-and-half or something like that.

Common wisdom has it that dump(1) is more resistant to these problems, but I haven't read the source so I'm not sure.

Personally, I do backups with tar, but duiring the night when those filesystems are not being used.

Filesystem snapshots will appear in the 2.3 or 2.5 Linux kernel series, I think, so in the end the problem will be solved the right way.

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jlms earned 140 total points
ID: 1637707
The problem of "live" filesystems is one of the filesystem you are using. Only a few recent filesystems allow you to do that, but Linux does not have them implemented (Veritas fs for example).

   So to be 100% in the safe side, you should back up filesystems that are not been used. Utilities like dump allow you to do so with the filesystem unmounted, which guarantees the fiabilty of what goes to the tape.
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