what about the Linux configuration (kernel, swap, memory settings, limits, etc)
are both servers the same type of hardware?
you mentioned 1 server has two filesystems, how are those configured?
might be the reading of the data devices which is slow instead of writing to the backup devices
I'd suggest to use compressed backups to minimize the amount of I/O
e.g. dump database SID to "compress::<path>"
or: dump database SID to "path" with compression=101
you can try different compression levels to see what suits you best
if you want to know if reading from the data devices is much slower, you might have a look at this trick from Rob Verschoor to dump to a null device.