[kwlug-disc] So why not tar -cf tarball.tar a.xz b.xz c.xz, instead of tar -cJf tarball.tar.xz a b c ?

[B.S.]

By itself, tar has no individual file integrity (checksumming) ability - 
albeit the entire tarball itself is checksummed when used, as 
traditionally, with compressors such as gzip.

I've read that tarballs can be fragile. And when damaged, there's no way 
to know which files remain undamaged. [Yet tar is the only archiver kept 
current with filesystems enhancements, such as ACLs, xattr, links, 
pipes, devices, etc.. Zip (also an archive) isn't, nor gzip, et al.]

Yes, md5's would also confirm integrity - while adding awkwardness and 
sidecar files to also track and validate.

So why is tar'ring gzip's instead of gzip'ping tarballs not more 
popular? [Google-fu fail.] Yes, it won't compress as much, but that 
seems a small price to pay for individual file integrity assurance.