I have 25 .tar files like: filename.tar.001 - filename.tar.025
When I want to unpack them with cat myarchive.tar.* | tar xvf - it does, but missing files: whole .tar is 1,2 GB, but unpacked files have just 600MB - I have ~200 files missing out of ~400.
Ive tared them using 7zip on my Windows OS: add to archive > .tar > 50 MB per part
Little image what I mean: 
--multi-volumeoption? – Zoredache Jun 25 '12 at 23:40