> if you use the -u (update) function in TAR to freshen an archive, what
> actually happens in the file? Is dead space created? Does the archive file
> increase in size each time it is freshened or does it rebuild the archive
> and just update the files that have changed?
The manual answers that question (if you understand unixspeak)
-u
only append files that are newer than copy in
archive
Unix world people use "append" specifically to mean extend the file. Since
there are no record based and btree file systems as the base fs in Unix
the meaning is unambiguous, unlike on many other systems
> So my options for backing things up are
> 1) Tar critical directory trees on a daily, weekly and monthly basis, FTP
> them to the HFS on s/390 so they get backed up by existant things.
> 2) Get NFS working on S/390 and Linux so that S/390 can mount my Linux file
> system and back it up.
If you have both S/390 and Linux/x86 boxes, and you can do tape dumps off
the Linux/x86 box then Amanda will do precisely what you need. You can do
tar backups over NFS, and I backup my home machines this way.
On the S/390 box edit /etc/exports (or use distro specific gui stuff) and
add
# Export to PC for backups - read any file, but no writing
/ a.b.c.d(ro,no_root_squash)
where a.b.c.d is the IP addresss of your PC backup box. Then do
exportfs -a
(to tell nfs to reread the data - only needed once)
on the client
mkdir /mnt/s390
mount s390:/ /mnt/s390
cd /mnt/s390
Then tar up the contents with something like
tar cvMf /dev/st0 .
If you are using something like DDS2/DDS3 tapes on a PC let the tape drive
do compression. A gzip file is lost beyond the first error which is bad for
backup tapes. The tape compression done by the drive is a little bit more
robust.
A second approach is on the S390 to do something like (untested)
tar cf - / | ssh mypcbox cat >/dev/st0
this keeps the data being backed up encrypted on the network and may well be
preferable in an insecure environment.
info tar has a few tutorials on tar and backup strategies. They won't teach a
sysadmin too many new tricks but they do give you good examples of the
command lines for each of them.
Alan
