[buug] Backups [Was: Trapped in Upgrade Hell]

Rick Moen rick at linuxmafia.com
Mon Mar 8 19:35:25 PST 2004


Quoting Nick Moffitt (nick at zork.net):

> 	Agreed. You may wish to look into rdiff-backup instead.  It
> does incrementals, and the last backup is always a "live" directory
> tree.  Go ape and back THAT up to removeable media for maximal peace
> of mind.

That's a good thought.

One refinement over incrementals that doesn't occur to a lot of people:
_Differential_ backups.

In an incremental scheme, there's (say) a Friday night full backup, and
then the subsequent four weekday incremental sets catch the changes from
Friday to Monday (Monday night tape), Monday to Tuesday (Tuesday night
tape), Tuesday to Wednesday (Wednesday night tape), and Wednesday to Thursday
(Thursday night tape) -- one day's worth of state, each).

The same scheme done with differential daily backups would load all
changes since Friday on Monday night's tape, all changes since Friday on
Tuesday night's tape, etc.  Each daily tape has all cumulative state 
since the last full backup.

And why would you do that, some would ask.  Because it reduces single
points of failure.

Example:  On Friday morning, your hard drive dies.  You mount a new hard
drive, and load the OS.  You restore the preceding Friday full backup,
then the Monday incremental, then the Tuesday incremental, then the
Wednesday incremental, then the Thursday incremental.  {Phew!}  You've
lost only a few hours of machine state.  Good!  

But suppose the Monday tape is bad?  Makes those next three days' tapes
pretty useless, doesn't it?




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