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Re: [Bug-tar] Unchanged directories in listed-incremental level 1

From: Joerg Schilling
Subject: Re: [Bug-tar] Unchanged directories in listed-incremental level 1
Date: Mon, 12 Jul 2010 20:47:28 +0200
User-agent: nail 11.22 3/20/05

David <address@hidden> wrote:

> Using gnu tar 1.22 on ext3 here, every level 1 incremental archive
> created contains an entry for every unchanged subdirectory. This
> disagrees with the expected behaviour described in the manual. Quoting
> from
> http://www.gnu.org/software/tar/manual/html_section/Incremental-Dumps.html#SEC94:
> "
> Some time later you create another incremental backup.  You will then see:
> $ tar --create --file=archive.2.tar --listed-incremental=/var/log/usr.snar 
> /usr
> tar: usr/local/db: Directory is new
> usr/local/db/
> usr/local/db/data
> usr/local/db/index
> The created archive `archive.2.tar' will contain only these three members.
> "
> Note it says: "only these three members".

>From my view, it it not really important whether the documentation matches
actual behavior. It is of course desirable that the documentation is right,
but does GNU tar _do_ what you expect?

If you like to trust in GNU tar incrementals, I recommend you to do a 100% test.
It is not really important what a program puts into the incremental archives.
The only thing of interest is whether the restore portation is able to re-create
the current state of a file system from scratch. That means, you need to test
with an empty disk, restore all needed incrementals in the right order and then
compare the original with the re-created new disk.

For a complete test, you need to:

-       create a set of files of all types and create a full backup

-       modify some of the files.

-       rename some of the files.

-       create some files of different type with the name of previously 
        renamed old files.

-       create some files with the same name and type of previously
        renamed old files. Take care to include populated directories
        with this test.

Then make an incremental backup of the modifications and later start
to restore.

After the incremental restore is ready, do a full compare of the original
and the re-created filesystem. Check whether there is no less and no more
files than in the original - besides the comparison.

I did this test with ufsdump/ufsrestore, star and GNU tar after I introduced
incrementals in star in summer 2004.

star did fully pass the test.

ufsdump/ufsrestore did mainly pass the test. There habe been a few problems
but I don't remember the exact cause anymore.

GNU tar did fail with renamed directories.

I did make a bug report at that time, bug I am not sure whether this has been 
fixed. So it may be worth to run a test with the current version.


 EMail:address@hidden (home) Jörg Schilling D-13353 Berlin
       address@hidden                (uni)  
       address@hidden (work) Blog: http://schily.blogspot.com/
 URL:  http://cdrecord.berlios.de/private/ ftp://ftp.berlios.de/pub/schily

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