On Mon, Dec 17, 2007 at 08:02:12PM -0800, Tracy R Reed wrote:
David Brown wrote:
Bacula falls under the list of "doesn't understand what an incremental
backup is". It's on their "not implemented page", but as far as I'm
concerned makes it utterly worthless. What exactly is the point of backup
software if it can't restore data that was on my machine at the time of
backup.
What is your definition of an incremental backup? I do not understand how
bacula cannot restore data that was on your machine at the time of backup.
As far as I can see that is exactly what it does.
A "full" backup is a backup that copies all file data to the backup
destination. An incremental is one that tries to not have to write all
data. However, it is important that when you restore the full and
necessary incrementals that the filesystem is in the same state it was in
before doing this backup.
This is not the case with bacula, as can be trivially demonstrated:
% mkdir aaa
% echo hello > aaa/file1
% echo there > aaa/file2
Perform level 0, wait at least a few seconds.
% mv aaa bbb
% echo goodbye > bbb/file2
Perform incremental backup. Try restoring it, you'll end up with both an
'aaa' and a 'bbb', with aaa/file1 and bbb/file2, and possibly aaa/file2
still having 'there' in it. Some programs even delete aaa/file1 and don't
put bbb/file1 in place, and other really bad things. Some are a little
smarter, and you have to put the changed entity down a directory.
No imagine that is in the middle of a large development project and some
directories have been rearranged. After a restore you're left with a
hodgepodege of files in random places often with little resemblance to what
the tree looked like at the time of backup. This kind of rearrangement is
very common on a machine that is used for software development.
Others may think this is useful, but I'm not sure what for. The Bacula
authors at least realize this is a deficiency, but don't seem to think it
is very important to fix. I guess I have some kind of silly expectation
that the purpose of a backup is to be able to restore it.
I had one machine whose backup was verifying with bad data in the middle of
a file. It was a single big. It ended up being bad memory in the
computer. I now consider it worth paying extra for ECC memory.
Dave
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