On Fri, May 16, 2003 at 07:10:20AM -0400, Mitch Collinsworth wrote:
> [many good points snipped]
>
> Oh, and for the record, if it's one or the other, my vote would be for
> tape chunking to be implemented first.

So would mine!  I don't think I'd give a hoot about taper
algorithms if chunking were implemented.  However...

> , there is still a significant
> problem domain for each one to solve by itself.

Significant, perhaps, but they're *not* equally difficult, IMO.

Tape chunking has been discussed to death a few times.  The net
result of those discussions is that it's highly desirable, and
clearly possible ... and it's a hard problem:
  - it's risky
  - makes it harder to restore with vanilla tools (which means it
    requires adding the emergency-restore-tarball feature that
    someone (re)suggested yesterday (good idea; but not needing
    it in the first place is even better :-))
  - too hard to get right (JJ's warnings about the evilness of
    tape)
  - too invasive:  it touches at least driver, taper, and
    amrestore; the driver/taper interface; holding-disk file
    management; maybe amrecover too
All the cons that have been raised over the years.

It's been on the most-wanted list since I started using Amanda
the first time around, circa 1995, but it still doesn't exist.  I
concluded that there are good and valid reasons for that, and
thus that it isn't likely to exist any time soon.  (I'm NOT
accusing anyone here; just trying to be realistic.)

The taper-algorithm enhancements, on the other hand, don't change
Amanda's fundamental assumptions, so they'll be a lot easier for
people to swallow.  More important, they're nowhere near as
invasive as chunking.  The changes are local to one program,
driver, and the interesting part is local to one *file*,
driver.c; the rest is just config-file parsing.

The taper-algorithm stuff seems to me to be a medium-sized,
un-dangerous, eminently doable task, that would make life easier
while we wait for the tape-chunking Godot.

--

|  | /\
|-_|/  >   Eric Siegerman, Toronto, Ont.        erics AT telepres DOT com
|  |  /
My Wine works.  However it crashes about half the time on startup.
Apparently their simulation of windoze API is getting too accurate.  :)
        - Kyle Sallee