Magnetic tape filesystem

[John Wilson]

On Mon, Feb 09, 2015 at 10:50:32AM +1000, Tom Sparks wrote:
>I am wondering if there were any magnetic tape filesystem?

I have a vague memory of hearing about something (one of the Unices maybe?
although handling tapes well is WAY out of character for them) that would
attempt to use 9-track tapes as block-replaceable media.  Which I think
meant using the "erase" command to add 3" of nothing after each block so
that you had at least some chance of rewriting that block w/o trashing what
comes after (this would cause a huge cut in capacity, but maybe I'm
misremembering the whole thing).  I've never seen this in person though,
and I'm a little surprised that it would work (maybe only on certain
drives?).

And as others have said, that's on top of intentionally block-replaceable
tapes like DECtapes (which act like disks), and file systems that accept
the tapiness of it all like ANSI or DOS-11 or CAPS-11 or OS-labeled tapes
(where you can write a fresh tail onto the tape from anywhere but you'd
better have a plan).  And almost everybody's got something like BRU or
:DUMP or SAVRES or tar which can store/retrieve archives of disk files on
tape -- but that's not the same as accessing tape files through the OS's
usual disk-file API.

John Wilson
D Bit