🚀 go-pugleaf

In article <4f6oej$mp9@steel.interlog.com> ldh@interlog.com (Laurent-Daid Hasson) writes:

>I have seen ONE product called TapeDisk that claims that it can make accessing a 
>SCSI tape drive as if it were a regular HD (besides performance of course). I 
>uess that what it does is to install a new file system and mounts the tape drive 
>as a drive letter. 

I use TapeDisk (or, as the authors quaintly call it, TAPEDISK).  It does 
indeed mount a tape drive as a DOS/Windows drive letter.

More specifically, it creates "chapters" on a tape and it can mount one of 
these chapters as a drive letter.  What is really powerful is what happens 
when you mount an existing chapter and start writing more files to it.  You 
can't rewrite the tape in place, so TapeDisk creates a *new* chapter at the 
end of the tape.  It writes only your changes to this chapter, but it writes a 
full file directory including both the data stored in the new chapter and the 
data in the original chapter.

From your point of view, the original chapter and the new one look like 
complete copies of your data, even though the new chapter really contains only 
the incremental changes.

TapeDisk includes some utilities that take advantage of this chaptering to do 
incremental backups.  This is completely different from the grossly inadequate 
way traditional backup programs do incremental backups.

With a traditional backup program, when you do an incremental backup, the 
program looks *on the disk* to see which files have not yet been backed up.  
Fine, but it only lets you do *one* incremental backup.

Suppose you have made two full backups, and now you would like to bring both 
these tapes up to date.  You can't do that with traditional incremental 
backups: you can only bring one tape up to date.  If you want to have two 
tapes that both contain complete backups, at least of them has to be a full 
backup, not an incremental.

With TapeDisk's chapter approach, an incremental backup backs up files that 
are not already on *that* particular tape.  So you can take two tapes, run 
"incremental" backups on both, and now each one is really in effect a full 
backup.

The only other backup program I know of that does this is Retrospect on the 
Macintosh.  It's really a puzzle that all the PC backup programs use the 
inherently flawed method of checking disk attribute flags.

-Mike (Mike@Geary.com, http://www.geary.com)