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What is an active cable?

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Applies to

NetApp AFF

NetApp FAS

Answer

Active cables are copper cables for data transmission that use a silicon chip (semiconductor) to boost the performance of the cable.

A copper cable without a chip is a passive cable.

  • Passive cables are liable to degrade the data they carry due to such 'channel impairments' as attenuation, crosstalk, and group velocity distortion.
  • In active cables, one or several semiconductor chips are embedded in the cable to compensate for some or all of these impairments.
  • This active boosting allows cables to be more compact, thinner and longer, and transmit data faster than their passive equivalents.

Benefits of active cables over passive cables include:

  • Reduced copper usage in cable production
  • Reduced form factor
  • Reduced cable weight (as much as 80%)
  • Longer reach (up to 5x more)
  • Lower power consumption (~75% less power than comparable fiber-based interconnects)

Summary of differences between active and passive cables:

  Active Cables Passive Cables
Power Powered Unpowered
Form

Thinner, lighter, longer

Up to 15-20 meter cable length

Thicker, heavier, shorter

Up to 12 meter cable length
Signal Loss Amplifies signal, optimized with variable level and peaking controls Signal integrity issues when length greater than 7 meters

Additional Information

How to identify if a SAS cable is active or passive:

  • In AutoSupport, view the SYSCONFIG-A section and look for "QSFP Type"
  • To see the same via the command line, run:
    • Data ONTAP operating in 7-Mode:
      • sysconfig -a
    • ONTAP:
      • node run -node <nodename> sysconfig -a

Sample output:

        slot 0: SAS Host Adapter 0a (PMC-Sierra PM8001 rev. C, SAS, <UP>)
                Firmware rev:       01.11.07.00
                Base WWN:           5:00a098:003531c:28
                Phy State:          [0] Enabled, 6.0 Gb/s
                                    [1] Enabled, 6.0 Gb/s
                                    [2] Enabled, 6.0 Gb/s
                                    [3] Enabled, 6.0 Gb/s
                QSFP Vendor:        Amphenol       
                QSFP Part Number:   112-00178+A0   
                QSFP Type:          Passive Copper 5m ID:01
                QSFP Serial Number: APF140817836DH
               
        slot 3: SAS Host Adapter 3b (PMC-Sierra PM8001 rev. C, SAS, <UP>)
                MFG Part Number:    USI 6086-000010-07 rev. MP V4.12
                Part number:        111-00341+G0
                Serial number:      ST063E5X096
                Date Code:          20140529
                Firmware rev:       01.11.07.00
                Base WWN:           5:00e004:0002e50:ac
                Phy State:          [4] Enabled, 6.0 Gb/s
                                    [5] Enabled, 6.0 Gb/s
                                    [6] Enabled, 6.0 Gb/s
                                    [7] Enabled, 6.0 Gb/s
                QSFP Vendor:        Molex Inc.     
                QSFP Part Number:   112-00242+B0   
                QSFP Type:          Active Copper (near and far end limiting active equalizers) 10m ID:01
                QSFP Serial Number: 93A422620499

 

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