rman/NFS over internet, performance

Hi,

I am trying to backup through an NFS mount to a disk located in a different datacenter between some solaris boxes. This works, but I am not satisfied with speed/performance. Using ftp, i can transfer data at more than 30mbit/s, while NFS peaks at only 16Mbit/s

I already use compressed backupsets. There doesn't seem to be a whole lot to tune in nfs client settings as oracle requires tcp, vers=3 and noac anyway.
I tried to use more (and less) parallel channels but that didn't help much either.

Any more ideas?

Thanks
Bjoern

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