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Synthetic backup questions

Created: 07 Feb 2013 • Updated: 08 Feb 2013 | 4 comments
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Hello, I'm thinking of implementing Synthetic backups on our regional sites as they currently use 3rd party software to sync down to a centralised location, and I'd like to get this all within NBU if possible, but I just have a few questions on how I should layout my policies...

My thinking is it takes a full backup, then differentials, and then when I do a synthetic full, this is essentially a full backup?

So if I were to do a policy with this:

1 - Initial seed, full backup to disk on NBU master server

2 - Daily diff - Mon-Fri

3 - Synthetic full to disk - Last Saturday

4 - Synthetic full to tape - Last Saturday

Will it then start reusing the synthetic full to disk, instead of the initial seed? So I can essentially have 1 full from the remote site as the seed, and then I'm done and don't have to pull 100GB of data from a 10Mb link? Or do I have to keep the initial seed? What retention should I use on the policies? Our general rule of thumb is Monthlies = 7yr retention... So I'd assume, on the initial seed (if I can use synth fulls to disk as the comparison after the 1st month) I set that to a 1 month ret, and then the synth full to tape, 7yrs, with the diffs at 6 weeks, like the rest of our diffs...



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Andy Welburn's picture

We changed all our backups recently to synthetic to disk - from the initial seed, the only time I've ever had to run a full from the client is if the differentials &/or synthetics start to fail & found that re-running a 'one-off' full corrected this. You could, resources permitting, throw in a proper full once a month but we haven't found the need.

Bear in mind also that your synthetic will be based on the last incremental - I initially did not realise this so our Saturday fulls were essentially Friday fulls. Got round this by scheduling an incremental just before the synthetic full.

Your retentions would be per your business requirements with the usual caveats.

Richard J Cunningham's picture

Thanks for the reply, so if I were to go with the above logic and whatever retentions I need, I should be fine - it's just a case of dumping it down to disk, and ticking the tick boxes in the schedules? Just making double sure. :)

Richard J Cunningham's picture

Another quick question, I'm assuming it's not allowing me to select the synthetic tick box because there currently hasn't got any backups in the catalogs yet...? Other policies have the option to enable synths.

Andy Welburn's picture

Have you got "Collect true image restore information" & "with move detection" boxes ticked in the policy? This is a requirement for synthetics.

Just for a bit of additional info, within any one of the schedules click on [Help] -> Schedule attributes field descriptions -> Synthetic backup. There's quite a few "Related topics" which could be beneficial e.g. "Recommendations" (don't use multi-streaming with synthetics) & "Policy considerations" (which covers the point I mentioned above).

As far as your (or my) "logic" is concerned, you should be fine - just test with one client if possible until you're confident that you're getting what you want (that's the route I took, 1 or 2 at a time) - & don't forget the synthetic will effectively be a backup from the time of the last incremental (this came to light for me when looking in the Backup, Archive & Restore GUI as no full backups could be seen on a Saturday that corresponded to the synthetics, they appeared on the Friday until I added the extra incremental just prior to the Saturday synthetic).