Tar Backups and Size Limits

[Joseph C. Lininger]

Hi,
First, allow me to clear up a little bit of confusion regarding limits of 
fat32. When you look at a filesystem, there are two major limits you will 
run into. The first is an over all limit, meaning how large the entire 
filesystem can be. The second limit is a bit more suttle. It is a limit on 
the size of an individual file. The fat32 filesystem can support filesystems 
up to 2 terabytes in total size. However, each individual file in a fat32 
filesystem may not be larger than 4gigabytes. Now, I will address Steve's 
original question.

The tar program is designed for tapes, and all the -f option does is to tell 
it to write the same contents to a file that it would write to the tape. 
This means that when it hits the size limit you have specified with -L it 
will simply start over with the next portion in the file. What you have to 
do to get around this if you want to do it this way is to have a script that 
runs in between each portion (see the -F option) which will rename the file 
tar uses for its work to something else so that when tar recreates it for 
the next part you don't lose the previous one. Tar does not automatically 
provide this functionality. I can provide more details on how such a script 
would work if desired.

You do have one other option. You could format the drive using ext2 or ext3, 
and then use ext2fsd under Windows to read and write the filesystem. The 
driver is not perfect, but it does work. This would overcome your size 
limitation. This would also allow you to use the -j option to tar since you 
would be using a single file, meaning the file would be much smaller since 
you would be using compression.
--
Joseph C. Lininger
jbahm at pcdesk.net
Verification: 5eab38a77ac40416e075be8f50607ff7
----- Original Message ----- 
From: "Steve Holmes" <steve at holmesgrown.com>
To: <speakup at braille.uwo.ca>
Sent: Sunday, November 07, 2004 1:24 AM
Subject: Tar Backups and Size Limits


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> Hey, I'm trying to backup my linux system (home directories to a 200
> GB external drive using tar.  It seems that there is an upper size
> limit either due to the fat32 file system on this external drive or
> tar.  I can't emagine tar having imposed any limits.  So I tried to
> use -M multi-volume option and a -L limit of 4GB.  It got through the
> first file seemingly ok and it put up the prompt to start the next
> file.  Well, I figured tar would just go ahead and create the next
> file with a different suffix or something.  Well, it appears that it
> did not.  When I looked in another console I saw that the size of the
> second archive started over as I would expect but it is actually the
> original file.  In other words, I think the back procedure is
> overlaying the first file.  The tar command I used is:
> tar -cvf archive.tar -M -L 4000000 FILES...
>
> I figured later I would do incremental backups against this tar file.
> Am I missing something? If I reformatted my external drive as ext3 or
> something, I could probably have done all this without size limits but
> I also intend to use this same drive to backup my winblows boxes as
> well.  This is a 200 GB drive with a pre configured VFAT single
> partition.
>
> Any ideas out there? Thanks.
>
> - -- 
> HolmesGrown Solutions
> The best solutions for the best price!
> http://ld.net/?holmesgrown
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