I agree with Hacketta1 & Axr2. That's way too many channels. Did it actually use all of them? Do you have that many devices in your tape system? RMAN should only use as many channels as devices available.

Another possibility - was anything else going on on your tape system at the same time? Other systems backing up? Reclimation? System level backups?

Whenever I have to restore, I always make sure my tape system stops all other processes for the duration of the restore.

Jodie