Is tape dead?

Mouse mouse at Rodents-Montreal.ORG
Tue Sep 15 12:41:42 CDT 2015

>> Delete it on the master and have it faithfully deleted on the replica.
> Backup should NOT be connected to the computer that it is backing up,
> and should be a drive, NOT a connected computer.

Depends on why you have backups - that is, what kind of trouble the
backups are intended to defend against.

I've identified three basic reasons to keep backups:

(1) "Oops."  This includes things like running rm in the wrong
directory by mistake.

(2) "History."  This is things like "okay, this was working last May,
what was in the config file then?" and "when was it we installed

(3) "Oh no."  This includes things like disk drives dying.

If anyone has a fourth reason to suggest, I'd be interested.  (Note
that getting cracked is basically a cross of (1) and (2) - and, indeed,
(1) can be viewed as a very-short-term form of (2).)

The thing is, for (3) you _want_ live replication, because you want
your replica to be as up-to-date as possible when a drive fails - but
for (1) and (2) live replication goes against the whole point (though
depending on how it's done it can be tool in the service of such
backups; historical backups can be done by freezing live replication
and saving offline copies of the replicas).

Thus, the answer to "are live replicas good backups?" is actually a
definite "maybe, depending on your threat model".

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