>docs/RAIT says two things that I'm confused about:
>
>   - "[RAIT supports only 3 or 5 drive configurations.]"  I have four
>     drives and no capacity for another in my library... this means I
>     should just remove one of my drives right?

Like any RAID setup, you need "N+1" drives where "N" is a divisor of the
data read/write size.  Internally, the tape code is getting (by default)
32KByte chunks of data, so "N" must be a power of 2.  The chunks have
to be split evenly among the "data" drives ("N") and then there needs
to be one more drive for the parity.

I'm not sure why the docs say "only 3 or 5".  As far as I know, that's
wrong.  I'm almost positive you can use 2 drives to achieve mirroring
(one data, one parity, which with a single drive turns out to be a copy
of the original).  And I don't know of anything in the code that limits
the striping to five (four plus 1).

>   - "currently it is only integrated with the chg-manual script." Ok
>     this means I have no hope of using my library automatically (eg,
>     as I could with chg-mtx if not using RAIT) ?

There is a new chg-rait in the current sources.  I don't know anything
about it, but I'd bet it's worth a shot.

>   - is anyone using RAIT in a production environment?

Marc Mengel (bless him!) at FNAL provided the RAIT code and as far as
I know is, and has been, using it in production for years.

>   - with just the tapes and no Amanda, is it possible to "destripe" a
>     RAIT set or otherwise get at the data?

It would be pretty tricky, and that's certainly something you should
consider before commiting to it.  One of the major benefits/features of
(non-RAIT) Amanda is that you can recover your data with only the normal
tools you get with a standard OS install (dd, possibly gunzip and whatever
the appropriate restore program is).  It's possible some clever script
(shell/Perl) programming, and a lot of testing, would be able to put
things back together again, but rather than go through that pain, I'd
make sure you keep a source copy of Amanda around that you can rebuild,
and/or keep the Amanda amdd binary around, which *can* read such tapes.

>   - is there a 2.5 tree somewhere with additional features?

Yes (as others have pointed out), but please understand that this is not
even alpha quality code.  This is where us developers go to play :-).
You're welcome to help test it :-), but you should not be surprised if
things go wrong and be prepared to help us diagnose what happened.

>Thanks.

John R. Jackson, Technical Software Specialist, jrj AT purdue DOT edu