[Gllug] XFS_repair cannot find master or secondary superblocks

[Martin A. Brooks]

Tethys wrote:
> 	A copy on disk is _not_ a backup.
> 
> That's rubbish.

A copy on disk is a copy.

A backup is an indexed archive that guarantees a point-in-time recovery 
of data to a time resolution decided by local policy. A backup is 
distributed, is stored off or near line, and is non-trivial to corrupt 
or delete.  A backup is on non-fragile media - a hard disk drive will 
almost certainly not survive dropping 1 meter onto concrete, a DLT tape 
almost certainly will.  A backup let's you see what changed, when 
(within the above set time resolution), and preferably whom it was 
changed by.

A backup is what you use when your data centre has burned down, all the 
hardware is beyond recovery and you somehow have to get your production 
systems operational again.

In this scenario if I turned round and said "Oh sorry, I copied all that 
important stuff onto a RAID5 set, well, that's sort of a backup, isn't 
it? And would you know it, it's corrupted on me!"  I'd expect to be 
stared at in wild-eyed disbelief followed by laughter as they realise 
that no-one, no-one who has ever dealt with mission critical data, ever, 
could possibly confuse a backup system for copying stuff onto a bunch of 
hard disks.

And then, as I have done mercifully few times before, I call up Hayes, 
who's number has been in my mobile phone for a long time, and say 
"Please send our last full backup set, and all the dailies since, on a 
bike as soon as possible please."



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