Networker backup server

Yes there is; CPU is required to push your drives to stream. Usually you have start from drive max speed, examine bus and supported speed and then calculate how much CPU power is required for that (don't forget additional CPU power required for NIC). These calculations may be different from vendor to vendor (I have seen it so far only for Sun and HP).

Here is a storenode driving a Tape Library with 6 SDLT600 Drives and the robotics.
I have a backplane problem and a CPU problem.
I am also backing up 60 odd machines to this Node daily.

Product Name ProLiant DL360 G4p
Processor Package 1 (Socket 1, Core = 1) Intel Xeon Processor @ 3.40 Ghz
Processor Package 2 (Socket 2, Core = 1) Intel Xeon Processor @ 3.40 Ghz
Operating system environment Microsoft(R) Windows(R) Server 2003, Enterprise Edition, Service Pack 2 (Build 3790)
Total memory - 4096 Mbytes
Board 0
DIMM 1 ( DDR ) 512 Mbytes (400 MHz)
DIMM 2 ( DDR ) 512 Mbytes (400 MHz)
DIMM 3 ( DDR ) 512 Mbytes (400 MHz)
DIMM 4 ( DDR ) 512 Mbytes (400 MHz)
DIMM 5 ( DDR ) 1024 Mbytes (400 MHz)
DIMM 6 ( DDR ) 1024 Mbytes (400 MHz)
ECC memory installed Yes
Hardware PAE enabled No
Serial presence detect (SPD) information - DIMM 1
Memory type SDRAM DDR2
Memory DRAM type RDIMM
DIMM Description SPS-MEM DIMM, 512MB, PC2-3200, 64Mx8
Spare Part Number 359241-001
Single-Bit Threshold Exceeded Status No DIMM errors detected
Multi-Bit Status No DIMM errors detected
Single-Bit Threshold Count 0
Multi-Bit Count 0
Serial presence detect (SPD) information - DIMM 2
Memory type SDRAM DDR2
Memory DRAM type RDIMM
DIMM Description SPS-MEM DIMM, 512MB, PC2-3200, 64Mx8
Spare Part Number 359241-001
Single-Bit Threshold Exceeded Status No DIMM errors detected
Multi-Bit Status No DIMM errors detected
Single-Bit Threshold Count 0
Multi-Bit Count 0
Serial presence detect (SPD) information - DIMM 3
Memory type SDRAM DDR2
Memory DRAM type RDIMM
DIMM Description SPS-MEM DIMM, 512MB, PC2-3200, 64Mx8
Spare Part Number 359241-001
Single-Bit Threshold Exceeded Status No DIMM errors detected
Multi-Bit Status No DIMM errors detected
Single-Bit Threshold Count 0
Multi-Bit Count 0
Serial presence detect (SPD) information - DIMM 4
Memory type SDRAM DDR2
Memory DRAM type RDIMM
DIMM Description SPS-MEM DIMM, 512MB, PC2-3200, 64Mx8
Spare Part Number 359241-001
Single-Bit Threshold Exceeded Status No DIMM errors detected
Multi-Bit Status No DIMM errors detected
Single-Bit Threshold Count 0
Multi-Bit Count 0
Serial presence detect (SPD) information - DIMM 5
Memory type SDRAM DDR2
Memory DRAM type RDIMM
DIMM Description SPS-MEM DIMM, 1GB, PC2-3200, 128Mx4
Spare Part Number 359242-001
Single-Bit Threshold Exceeded Status No DIMM errors detected
Multi-Bit Status No DIMM errors detected
Single-Bit Threshold Count 0
Multi-Bit Count 0
Serial presence detect (SPD) information - DIMM 6
Memory type SDRAM DDR2
Memory DRAM type RDIMM
DIMM Description SPS-MEM DIMM, 1GB, PC2-3200, 128Mx4
Spare Part Number 359242-001
Single-Bit Threshold Exceeded Status No DIMM errors detected
Multi-Bit Status No DIMM errors detected
Single-Bit Threshold Count 0
Multi-Bit Count 0
Communication
Serial Port 1 (Address 3F8h)
USB Device 1 USB UHCI Root Hub
USB Device 2 USB Mouse
USB Device 3 USB UHCI Root Hub
USB Device 4 USB EHCI Root Hub
USB Device 5 Intel(R) 6300ESB USB Universal Host Controller - 25A9
USB Device 6 Intel(R) 6300ESB USB Universal Host Controller - 25AA
USB Device 7 Intel(R) 6300ESB USB2 Enhanced Host Controller - 25AD
Network Controller 1, Slot 0 NC7782 Gigabit Server Adapter
Network Controller 2, Slot 0 NC7782 Gigabit Server Adapter
Storage
Diskette Drive 1 HighDensity 1.44
Optical Drive 1 TEAC DV-28E-N at Primary/Master
Physical Hard Drive 1, Controller Slot 0 146.8 Gbytes 10K RPM - COMPAQ BD14689BB9
Physical Hard Drive 2, Controller Slot 0 146.8 Gbytes 10K RPM - COMPAQ BD14689BB9
Tape Drive 1, Controller Slot 48 HP SDLT600
Tape Drive 2, Controller Slot 48 HP SDLT600
Tape Drive 3, Controller Slot 48 HP SDLT600
Tape Drive 4, Controller Slot 48 HP SDLT600
Tape Drive 5, Controller Slot 48 HP SDLT600
Tape Drive 6, Controller Slot 48 HP SDLT600
Logical Disks
C: Logical Disk 1 ~ 52.43GB
D: Logical Disk 2 ~ 94.38GB
PCI Slots
PCI Slot 1 In Use
PCI Slot 2 Available

checkou the Performance Tuning Guide

The best place to start is the tuning guide. It also has the OS parameters recommendations which can help with your backup / recover performance.