[BBLISA] Definition of dump levels?

[Brian O'Neill]

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: bblisa-bounces at bblisa.org [mailto:bblisa-bounces at bblisa.org] On
>> Behalf Of Scott Ehrlich
>> Sent: Saturday, January 05, 2008 8:33 AM
>> To: bblisa at bblisa.org
>> 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
>>
>> _______________________________________________
>> bblisa mailing list
>> bblisa at bblisa.org
>> http://www.bblisa.org/mailman/listinfo/bblisa
> 
> _______________________________________________
> bblisa mailing list
> bblisa at bblisa.org
> http://www.bblisa.org/mailman/listinfo/bblisa