I've seen conflicting definitions of what "Incremental" and
"Differential" are. What I always knew as the "classical" definition
(and what I always taught when I did) was that Incrementals were the
backups of any data changed since the last backup of ANY level.
Differentials were the backup of anything since the last full only -
thus Differentials would be larger than Incrementals over time.
Veritas Netbackup I believe defines it the other way.
Using my "classic" definition, dump levels are essentially a hybrid.
Level 1 is ALWAYS a differential, since the only level below that is 0.
Any other level done continuously would also be a differential from the
most recent lower level.
To get a true incremental using dump levels, you need to increase the
dump level each iteration - do a level 0, then a 1, then a 2, etc.
An old pattern I used was a 0 on the first Saturday of the month, then 1
through 4 through the remaining Saturdays. During the week, I'd skip
Sunday (little changed), and then levels 5-9 at night. Thus, everything
but the first was an incremental, saving time (and tape), but it mean
reading up to a max 10 tapes to do a restore.
Nowadays, with autoloaders and such and smarter restores, its less of an
issue going through a number of tapes. Legato Networker uses dump
levels, but also has a separate "incremental" setting (which uses my
"classic" definition), and I've used both Monthly fulls and Weekly fulls
with incrementals the rest of the way without problem.
Edward Ned Harvey wrote:
A dump of any dump-level will backup all files that have changed since the
most recent dump of a lower dump-level. This is basically an unnecessarily
large level of abstraction, the guys who originally wrote it were thinking
*way* broader than necessary.
There's a nice simple analogy, if you're familiar with Full / Incremental /
Differential backups.
* Think of a Full Backup like level 0. It gets everything no matter what.
* Think of a Incremental like level 5. It gets everything that changed
since the last full, and creates an intermediate stage, so your
differentials/level 9's don't have to copy that stuff again.
* Think of a Differential like level 9. It gets everything since the most
recent 0 or 5.
Depending on how much data you're talking about, you might do something like
this:
Run a daily script, which does this:
If today's the 1st of the month,
Do a level 0.
Else:
If today's Sunday,
Do a level 5
Else:
Do a level 9
That would get you your Monthly fulls, Weekly incrementals, and daily
differentials.
As mentioned by John, most people don't have a large enough quantity of data
to mess around with Incremental/level 5. Most people will do something like
weekly level0, and daily level9.
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Scott Ehrlich
Sent: Saturday, January 05, 2008 8:33 AM
To: [email protected]
Subject: [BBLISA] Definition of dump levels?
I've seen so many references to dump levels, but none of them,
including the
man page, actually says what, specifically, each level covers.
For example, a level 0 would presumably back up everything. But will
it still
do so if I perform a level 0 today, update /etc/dumpdates, then perform
another
level 0 just after, and no files have changed?
What about the other levels? What do they do?
Thanks.
Scott
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