sparse files

[Roger Oberholtzer]

On Sat, 2005-05-21 at 12:37 +0800, Man-wai Chang wrote: 
> > Next I wanted to copy the image to another computer. So, I thought I
> > would use tar's --sparse option to make a file to copy, and then untar
> > it and have the sparse file on the other computer. Nope. The untarred
> > file stops at 2GB. So, I thought I had some file size limit. So, I tried
> 
> What file system does your target system use?

Same as the source - ext3.

The sparse file is not re-created correctly on the same system the
original sparse file exists. The odd thing is that if the original
sparse file contains, say, 500MB of actual content in a 6GB sparse file,
the recreated sparse file is always 2 GB. Could it be that there is a
2GB limit on the ext3 file system that does not apply to sparse files? I
wonder what would happen if I tried to fill the sparse file with more
than 2GB of content. I also need to check if the file created by tar is
really sparse. Anyone know how to fine how much space is really used in
a sparse file?

What confuses me is that all the discussions of this are joyous about
how well tar does this. Many predate the newer file systems, so I guess
they are for ext2/3 file systems. Sadly they seldom tell.

I will experiment a bit more. 

-- 
Roger Oberholtzer <roger at opq.se>