Has Best compression any advantage over Optimal?

[pizang]

I have just upgraded my VSphere+Veeam server to 8 cores (3GHz) and 16 GB Ram (from 4 cores and 8GB). I have tried to run test backup of our fileserver (1,2TB in 3 VMDKs) with best compression.

Results:

Optimal - 458GB
Best - 440GB

As you can see difference is pretty small. To small for such a change in the name of compression option (Optimal->Best). Can anyone see bigger difference? Does anyone use best compression?

[Gostev]

Yep, obviously compression ratio depends heavily on actual content, so with other VMs it can be more or less.

But, is there any reason NOT to use Best compression it if you have powerful server? That is 4% win in your case, this is a lot to me. If you have plenty of storage and backing up locally, 40GB of savings for every 1TB of backups may not be big deal. But as soon as you have to archive to external storage, copy backups to remote DR sites or cloud storage over WAN, this will make difference...

[AJ83]

Best compression can also boost backup speeds.

Our target storage is not that fast, and our Veeam server has enough CPU power to handle best compression. Because it has to write less data, the resulting backup speed is higher.

So, when target storage is the bottleneck, go with best compression.

[pizang]

I understand that but do you have any numbers? 4% in my case is something but is not significant. Maybe in your case you have higher difference?

[Gostev]

That would depend on the VM content, but I expect 4-5% to be good and typical average.

Please help me understand what you are primarily concerned with? Are you concerned with CPU usage because you want to share the Veeam Backup server with some other service? In that case, you should go with Optimal not to have your backups affecting the other service. But, if you have dedicated server - then really no reason not to go with Best really.

[alecprior]

We saw between 30% and 50% reduction in size when switching from Optimal to Best compression. The load on the veeam server is high though (60%+ cpu and high ram usage). As such the time taken to do the veeam jobs is not significantly shorter. We save the time on the run to tape (we do this every night).

[Gostev]

Alec, I am not sure what version are you referring to, but please note that in v3 Optimal compression was using different algorithm. In v4, the difference between Optimal and Best is expected to be smaller, see here for more information on this change: Compression level changed in v4?

[pizang]

Gostev: I am just curious why it is so small - there is a huge difference between low and optimal and very small between optimal and best. You know, this is suspicious .I understand your point, and when I will have a new storage I will recreate jobs with best compression.

[Gostev]

Why suspicious?

This is exactly why we call optimal compression "Optimal" - because it provides the best CPU to compression ratio for average modern server and FC4 SAN storage.

In order to compress the data further (Best), you will need twice as much CPU power - and compression ratio will not increase significantly, because for any data compression ratio, the curve is exponential. Meaning, you will get huge difference in the beginning, but the further you go, the less size decrease you get for CPU cycles you spend - until you reach the point where you cannot really compress your data any longer. Of course, we do not go that far on the curve, our "Best" compression ratio is optimized to keep higher-end servers busy (not overloaded) when processing FC4 SAN jobs.