[BBLISA] Definition of dump levels?

[Edward Ned Harvey]

> - Do I use tape 1 for all backups?
>  	- If yes, I perform a level 0 on it.  I then perform a subsequent
>  	(/dev/nst0) level 9 to it.  Will dump complain that a level 1
>  	doesn't exist and force a level 0 again?

Although I personally only use level0 and level1, the selection of
dumplevels is pretty much arbitrary.  I could do 0+5 instead, with the same
result.  Or 0+7, or 0+9, or whatever.  The system will not complain about
doing a level 9 when the most recent backup was a level0.

In fact, you never have to do a level0 either (although it is conventional.)
Let's suppose you create a weekly level5, and a daily level9.  Then your
level5 is your full backup, and your level9 is incremental/differential.

The one thing you need to remember is:
* Every dumplevel will copy all the files that have been changed since the
most recent backup of a lower dumplevel.

This means dumplevel 0 will always get everything (there is no number lower
than 0.)

For now, just to avoid confusion, I'm going to recommend 0+9.  If you
discover that your daily level9's are growing too large, then revisit the
issue to figure out how to intermingle some intermediate dumplevels.

Regarding which tapes to use, and overwrite versus append - I think you'll
have to make this decision on your own; you can do it any way you wish.  If
you want, you can put level 0 onto tape 1, and then append level 9 after it,
or whatever.  Each level9 can overwrite the previous level9, or just append
again.  Same tape, or different tape.  Your call.  I positively recommend
*testing* your backups regularly, by actually *performing* a restore.

Personally, what I do is this:

On Saturday I create a level 0.
On Sunday I create another level 0 on a different tape.
On Mon-Fri, I create level 1's ; all on different tapes.

When I arrive to the office on Monday, I take Saturday's tape offsite, and
replace it with a fresh blank tape.  But Sunday's level0 stays onsite,
because it could be needed for a restore.  

The next Saturday it all starts over again.  I never append; only overwrite.
I'm not scared of overwriting, because every week I have another full backup
offsite.

In retrospect, it would have been smarter for me to choose level 0+9 instead
of 0+1, because 0+9 allows more freedom to restructure your backups at a
later date.  If I discover that level1's get too large, my only recourse is
to get rid of level 1, and start using something like 0+5+9.