As to TOP's question, have you tried running a full, then a series of
incrementals, THEN a syn full or cumulative incremental? That's what
it's designed for. Why would you make a syn full from a full? The
results would be the same a duplication of that same backup, with a lot
more work. The use of it without any fulls is pointless enough that the
program is probably just barfing and saying "what are you doing? You
don't have any incrementals to merge into a full! All you have is a
full! Why don't you just copy it?"
To the question of what synthetic backups are for...
The purpose of NetBackup's Synthetic Backups is to allow you create a
full or cumulative incremental backup without having to transfer the
files across the network. The definite benefits are reduction in load
on the client and network, and that you can create the full/cumulative
backup any time of the day -- you can't do that with regular fulls. It
may or may NOT take shorter than a traditional full or cumulative
incremental backup. IMHO, Symantec oversold the "quicker" aspects in
the early days of Synthetics, and created a lot of unhappy people
because in some circumstances they take longer. They're still BETTER
(no load on the client or network, and run them at any time.)
In order to create a Synthetic Full/Cumulative backup, NBU wants to have
on tape all of the files in the condition they currently exist on the
client being backed up. In order to do that, it must perform an
incremental. Otherwise you'd be creating a full backup based on files
that were backed up at some previous point in time, so your synthetic
backup would look like it was taken yesterday or before. Therefore, NBU
requires you to take an incremental just before.
Bringing TSM into this comparison muddies the waters, IMHO. First, they
have a completely different architecture that doesn't require fulls for
filesystem backups. You have to do other things that NBU doesn't need
to do, like reclamation, but you don't need to do fulls.
The closest thing TSM has to a Synthetic Full Backup is a "Backup Set,"
also referred to as an "instant archive." A Backup Set is a self
contained tape that can be read and restored from without the TSM
database, and consequently, its contents are not stored in the TSM
database. So a Backup Set cannot be used for regular operational
restores inside TSM -- it is designed to be used outside TSM.
When you compare a Backup Set to a Synthetic Backup, they are very
similar. Perform a recent incremental, then create your Backup Set.
Although TSM doesn't require it, it would be silly to do otherwise,
unless you were trying to create an archive from several days ago.
---
W. Curtis Preston
Backup Blog @ www.backupcentral.com
VP Data Protection, GlassHouse Technologies
> -----Original Message-----
> From: veritas-bu-bounces AT mailman.eng.auburn DOT edu [mailto:veritas-bu-
> bounces AT mailman.eng.auburn DOT edu] On Behalf Of Haskins, Steve
> Sent: Tuesday, February 19, 2008 7:02 PM
> To: VERITAS-BU AT mailman.eng.auburn DOT edu
> Subject: Re: [Veritas-bu] Question about synthetic backups
>
> CBergen,
>
> You're not the only one that would like some enlightenment...I mean,
> on synthetics backups. I don't understand why incrementals have to be
> continuously run at all. As I understand it, that is the point of
> synthetic backups as to have a full and just backup the changes from
> that point forward with synthetics? That is the way TSM's synthetic
> backups work with the option of how many 'versions' to retain. I'm on
> 5.1 (getting ready to upgrade to 6.5.1) so maybe synthetics are
> different in 6.x? What is exactly done between the required
incrementals
> and the synthetics? Does each synthetic combine the previous two
> incrementals and how; as a differential and then expire the two tapes
> that were used for the incrementals (just an example if two were
used)or
> delete the incrementals images on the tapes OR disk?
>
> Regards,
> Steve
>
> -----Original Message-----
> From: veritas-bu-bounces AT mailman.eng.auburn DOT edu
> [mailto:veritas-bu-bounces AT mailman.eng.auburn DOT edu] On Behalf Of
dbergen
> Sent: Tuesday, February 19, 2008 12:20 PM
> To: VERITAS-BU AT mailman.eng.auburn DOT edu
> Subject: [Veritas-bu] Question about synthetic backups
>
>
> When I attempt a synthetic backup and the most recent backup of the
> client is a full backup nothing happens.
>
> Nothing happens because Netbackup says there was no incremental backup
> to analyze. My question is: So What?
>
> I want another full backup, to a completely different volume pool,
> shouldn't Netbackup realize that the volume pool is different and run
> the synthetic backup again?
>
> Hopefully someone can tell me what I am doing wrong here.
>
> Thanks,
> dbergen
>
>
+----------------------------------------------------------------------
> |This was sent by dbergen AT cucbc DOT com via Backup Central.
> |Forward SPAM to abuse AT backupcentral DOT com.
>
+----------------------------------------------------------------------
>
>
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