On 27-May-98 Stephen Carpenter wrote:
> On Tue, May 26, 1998 at 10:15:58PM -0600, Lazar Fleysher wrote:
>> Is it possible to create a file system on a tape drive ( like on
>> mainframes) and use it as a disk? I know it is very slow, but is it
>> possible?
>
> That is really very sick and twisted to even think of such a thing...
> hmm I wonder why I never thought of it :)
Of course it CAN be done (and when tape was the main storage medium for larger
archives it often was done). But only dire necessity would justify setting up a
fullly functional file system on tape, because of the sequential access.
For instance, you can't readily recycle freed-up space on a tape after
"deleting" a file: OK if the next file to go in is shorter than the freed space,
but if it's longer then either it all goes at the end (if there's room) or part
goes in the gap and the rest at the end/next gap, which might mean several
minutes to reposition for the next chunk of the file; and collating the logic
required to simultaneously retrieve several files stored fragmentally in this
way is likely to lead to mental dysfunction of the programmer ("sick and
twisted" indeed).
>> If not, is it possible to have several files on one tape and how to
>> access them?
As Steve says, tar + mt provide the basic tape resources for reading, writing
and positioning. You could reserve a fixed size block at the beginning to store
a file as a "pseudo directory", say with space for 1024 entries each with 256
bytes, so you get filename, size, date and sequential position[s] on tape. You
read this off first and use it to plan the rest of the operations. When you've
changed the tape contents you update this "directory" and write it back to its
old position. You could even organise fragmented storage this way ...
Ted.
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E-Mail: (Ted Harding) <[EMAIL PROTECTED]>
Date: 27-May-98 Time: 21:37:37
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