synthetic fulls 1

[Dougieoz]

Hi all,
I was wondering if someone could clear up a debate i'm having about synthetic fulls.
I will explain it in a scenario, its easier

All backups are going to magnetic storage.
If you do a full backup on the sunday night to backup all the files, a file is created on the monday, and an incremental backup captures that change on the monday night. The file is then deleted on the tuesday, and you run a synthetic full on the tuesday night. If i pruned the full and incremental created on the sunday, and monday, would i be able to recover the file from the synthetic full?


Thanks

D

 

[birky]

Hi

Do you mean pruning the Sunday Full and Monday Incr before or after the Synth Full runs on Tuesday?

If pruning after the Synth Full runs on Tuesday then Yes, you would be able to recover the file from the synth full because the synth full would just take the last Full (Sunday) and apply the incremetal (Monday)to it to create a new Full.

But, if pruning before the Synth Full runs then this would be different because the Synth Full looks for the last Full and associated Incr's to create the Full...so your Synth Full would be created from earlier backups resulting in the file not being found.

 

[Dougieoz]

Hi Birky,
Yes if i was to prune the full and incremental after the sync full, would we be able to recover the file?
Remember we dont have any aux copies of the full or the incrementals, and they are sitting on mag.

Cheers

D

 

[birky]

In a nutshell, Synth Full just creates another Full (without going back to the client) so until you prune Sundays Full you will have 2 Full backups held on maglib...so when you prune Sundays Full you will just be throwing away the earlier Full and the latest will still be on maglib.

Of course...this is also reliant on the retention that you set.

Hope this makes sense mate ;-)

 

[Dougieoz]

ok thanks Birky.
So basically the synthetic full creates effectivly a normal full backup from the prvious jobs, without having to run the scan, and transfer data across the wire from the client.
If you were to prune the full from sunday, and incrementals from monday after the synthtic full was created you would lose the file created on the monday.

Cheers

D

 

[birky]

1)Yep, a Synth Full takes the last Full and rolls up all related Incr's to create a new Full.....this is done through the Media Agent so doesn't touch the client again.

2)Nope you wouldn't lose the file as it will have been captured in the Full created by the synthetic full on the Tuesday...dependant on retention of course ;-)

 

[Dougieoz]

Hi Birky,
Thanks for the clarification.
I tested this and yes you are able to recover the file.

Regards

D