>All of this discussion concerning primary backup to tape ignores
>the unreliability of tape, particularly as a primary storage
>medium.

I don't think anyone's arguing that tape should be the only media
-- in fact, ADSM operates much better if given even a small disk
staging area. The issue really turns on capacity for the
staging area. The issue really turns on capacity for the
price. The same amount of money that buys a optical jukebox in
the hundreds of megabytes will buy several terabytes of tape
storage -- on a large scale, the cost per byte of tape is still
so favorable that it's the secondary storage medium of choice. I
will agree that optical storage is certainly appropriate for
archival storage, however I hesitate to agree that it is more
appropriate than tape due to the high cost per byte stored.

> Tape should not be used as a primary storage medium.  It is only effective
> when data is streamed to the tape from beginning to end.

Our observations in use disagree with this conclusion. If the
tape transport supports block positioning, as the 8mm and 3x90
devices do, tape is very effective in this kind of application.
The paradigm is to consider tape as _secondary offline storage_.
You still need disk as random-access space, but only for catalog
lookup and staging space.

> Use disk - optical, or magnetic - where it is necessary.
> Attempting to use tape in its place is a false
> economy.  You will lose your customer's data and will have
> saved only pennies.

A properly managed tape library is as reliable as any other
removable media. Even the cost of a 3590 -- which is significant
-- is still peanuts compared to a optical library jukebox. The
difference is in the tens of thousands of dollars, not pennies,
difference is in the tens of thousands of dollars, not pennies,
and the capacity of the jukebox is limited by the number of
optical cartridges that can be accessible to the robot at a given
time. Tape devices are limited only by the storage space
available for the tape library, a much less expensive resource
(unless you live in Tokyo!).