Quote Originally Posted by naqi76
The netbackup admins, use the netbackup gui tool and see that the total rate is at 50mb/s for the full db backup - no matter how many channels are allocated. You would think with 3 drives id at at least be able to get 150mb/s - however according to the netbackup admins the total backup shows a rate of 50mb/s. See what appears to happen is as additional channels are allocated the total 50mb/s is divided over all the channels, one channel may operate at 15, another at 25 and the third at 10 giving a total of 50. if we stick to two channels, each channel would more or less give a rate of about 25mb/s - sticking to the total of 50mb/s.
Which makes you wonder why can't we get over 50mb/s. I'm going to have access to this system to run iostat to see whats going on myself - hopefully that might reveal some sort of io issue.
Then your limiting factor is how fast you can pump the data to the backup device. Typically, mb/s means mega bits/second. If your rate is 50 mega bits/second, that is pretty poor. If it is 50 mega bytes/second, that you might be doing OK. (Granted 400 Mbps on a gigabit ethernet is not fully utilized, but coming from one interface it might be OK).

Could you please elaborate on: 'Your backplane may be the limiting factor if you're trying to spin X tape drives and Y disk drives.'
Sure, your computer's backplane/bus can only move so much data. If you have a bunch of devices hooked to it locally the bus speed may limit how much data you can move. However, since you're backing up over the network, I'd say this is most likely not the problem.

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To me the backup being written will only be as good as what rman can read (keeping all else sane)
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Take rman of the picture. Use a plain filesystem copy to backup the datafiles across the network and see what the speed is (Of course, you can't use this as a real backup, but you'll be able to compare time/throughput). If rman is the problem, you can fix it. If rman is not the problem, your network admins need to fix it.

Use rman to backup to a local disk and time it. That will tell you how fast rman can pump the data. (Note, you will have to make sure the local disk can support that level of write activity so the disk is not the bottleneck).