[BBLISA] Definition of dump levels?

[Edward Ned Harvey]

> -----Original Message-----
> From: bblisa-bounces at bblisa.org [mailto:bblisa-bounces at bblisa.org] On
> Behalf Of Brian O'Neill
> Sent: Sunday, January 06, 2008 8:41 AM
> I've seen conflicting definitions of what "Incremental" and
> "Differential" are. 

Perhaps Legato Networker is different from other commercial products that
I've seen, but until I hear otherwise, I'm assuming Legato uses the same
terms the same way as the others.

I understand that according to the dictionary and layperson understanding of
those terms, it's not clear what exactly they mean.  They're used a lot (and
loosely) in layperson conversation, and that makes it still more confusing.
What I'm considering to be the "right" way of thinking, in the context of
filesystem backups, is the way of thinking that will help system
administrators avoid backup problems.

I believe all "official" uses of those terms are consistent with each other.
For example, in NTBackup, BackupExec, ARC Brightstor, and Yosemite.  All
commercial products that I know use the terms "Normal," "Incremental," and
"Differential" consistently, and all the documentation describes it
consistently and accurately.

"Normal" backups copy everything.
"Incremental" backups copy everything since the most recent Normal.
"Differential" backups copy everything since the most recent Normal or
Incremental. 

Implementations may vary.  Some systems use the archive bit.  Some systems
use "file modified" timestamp.  People argue in favor of one implementation
or the other, and they all have valid points, but the core idea Normal vs
Incremental vs Differential remains the same.