Synthetic Full & Aux Copy Performance

  • 5 December 2021
  • 3 replies

Userlevel 1
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I do several 10-20TB synthetic full jobs each week which are then aux copied off to tape on a global tape copy policy with a single stream (one LTO drive) with multiplexing enabled.

I noticed that under the advanced settings on the synthetic full job the “Use Multiple Streams” option is NOT selected.

What I think this means is that each 10-20TB synthetic full backup gets written to disk as a single stream which means it gets aux copied to tape as a single stream.

If so am I right in thinking I want to enable this setting so the synthetic full jobs get written as multiple streams as this means they’ll get aux copied as multiple streams?

I’m going to be moving the DDB to a new NVMe volume which seems a good time to review things.

We’re on 11.20.73.

Thanks in advance.


Best answer by jgeorges 6 December 2021, 00:25

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Userlevel 5
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Hi @Paul Hutchings 

Take a read here re: Multi Stream Synthetic Full:


Provided your doing both File System and Virtual Server and are leveraging V2 indexing, than you would want to enable as the more source streams associated with the Synthetic Full, the more Destination Streams. This ultimately increases throughput.


NB: Ensure you understand that when Multiplexing data to tape, Write Performance is improved, as we are striping data, however as a consequence of striping data, restore performance is severly impacted.

If you have more than 1 drive, consider combining to x streams (1 stream for every drive available) and reduce or eliminate multiplexing entirely OR set the recovery expectations accordingly.



Userlevel 1
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Jase thank you, I had read that and of course it looked as simple as just tick the box.

I wanted to be sure there were no downside to ticking it.

As you say multiplexing maybe but that’s the case already :grinning:

Userlevel 6
Badge +18

I wanted to be sure there were no downside to ticking it.

The only “downside” is it consumes more streams.  Generally, though, the added performance for the Aux Copies is well worth it.  Remember the agent needs to be running V2 Indexing.