Stephen,

> I am running BackupPC 3.1.0 on Nexenta.  It seems to be working for the 
> most part.  I am having a problem with BackupPC_tarCreate.  I am trying 
> to create a tar of a 30gb backup.  The tar I create ends up being 30gb, 
> but when extracted it only takes up 5gb and is missing a lot of files.  
> I can restore the missing files using the web interface, so I know that 
> they are being backed up and that BackupPC has permission to access 
> them.  Does anyone have any idea what's going on?  The only clue I have 
> is that I repeatedly get "tar: Skipping to next header" when untaring 
> the file.

There appears to be some problem with the file header that precedes
each file in the tar archive.  If a file header field (most likely the
file size) isn't written correctly by BackupPC_tarCreate or interpreted
correctly by tar, then it will have symptoms like you see.  Similarly,
if the size of the file written to the archive doesn't match the size
in the header you will see the same problem.

The challenge is debugging this with such a large archive.

First, what version of tar are you using?

If you run:

    tar tvf largeArchive.tar

please look for the first error message.  This should be +/- one
file of where the first corrupted (or mismatching) header is.

You could then try making an archive with just that file in it
(maybe also with the prior file or two).  Is that one bad too?
If so, is it small enough to send to me?

Alternatively, you can repeat with tar's -R option which should
show the block number close to the first bad header.  You could
then use dd to extract the file headers just before, at, and just
after the problem. Those would be small enough to send to me for
inspection.  I'd need to know the correct uncompressed size of
each of those nearby files too.

Craig

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