[CLUE-Tech] Tape Drives - why?

[David Anselmi]

Eric Jorgensen wrote:
[...]
> Let's say that you have to go back to "last Tuesday,
> 'cuz I think I deleted the file on Wednesday." 
> Unfortunately, in our jobs, this does come up!  So if
> you're doing a simple rsync, you've just rsync'd over
> the data you need.

I saw a script a guy used with rsync.  He would rsync a directory tree 
into a "current" backup directory.  Then the next day he would copy that 
(using hard links) to a "yesterday" tree and rsync a new current.  The 
next day "yesterday" became "two days" ago (just a plain mv), "current" 
became "yesterday", and a new current was rsync'd.

This is a copy on write sort of scheme.  If a file has changed, rsync 
writes a new copy into the current tree (of the whole file, though only 
changed blocks cross the network).  If a file hasn't changed, rsync 
leaves it alone and it is pointed to by all the backup trees that use it.

Not quite as nice as filesystem level snapshotting, but not bad.  And 
allows you to go back to "last Tuesday".  Perhaps what you meant by 
"difficult but doable".

Dave