Re: missing files from incremental backups

Lasse Kliemann <[email protected]> wrote:

>
> Experiment:
>
> One process repeatedly generates a random filename and then touches, removes 
> or writes a files by this name (which can result in an existing file to be 
> modified). In other words: we have a very simple simulation of an active 
> filesystem.

This is a case, that cannot be handled correctly without using a fs snapshot
for the dump.


> While this goes on, incremental backups of levels 0 to 9 are done with the 
> following command:
>
> star -c -xdev -sparse -acl -link-dirs level="${level?}" -wtardumps \
>   f=level-"${level?}".star -C "${mount?}" .
>
> Then, the generating process is stopped and one final backup of level 10 is 
> made. Nothing modifies the filesystem during this.

If files in a directory are removed/renamed or created after the directory 
namelist has been read using readdir() and before star archives them, many 
things may happen.

As star uses fetchdir(), all files that miss after the readdir has been done
will create a warning. If the file system may reuse the inode numbers for 
other file names that did exist before with a different inode number, anything
may happen. Star is not better than the OS you run it on. If you like to backup
a life filesystem use snapshots.


> A copy of the backed-up filesystem is made using `cp -a' (from now on called 
> `the copy'), then the filesystem is deleted and restored with the command 
> from the manual page:
>
> cd /filestem-mount-point 
> star -xpU -restore f=...
>
> applied to files level-0.star up to level-10.star. During the restore, there 
> are several warnings like this one:
>
> star: WARNING: No new inode number for /alive/file_391
>
> Then the copy is compared to the restored filesystem.

See above, anything may happen. Better use snapshots.

Jörg

-- 
 EMail:[email protected] (home) Jörg Schilling D-13353 Berlin
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       [email protected]     (work) Blog: http://schily.blogspot.com/
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