• Slow transfer of data to back-up
  • Retrieval time to restore
  • Off-hour processing and monitoring
• Server disk space expands over time
• Loss of data between last back-up
• Physical security of tapes

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Single Points of Failure

• Cabling failures
  • Coaxial – many workstations or servers attached to the same segment of cable, which creates a single point of failure if it is broken
  • Exceeding cable length is a source failure
• Twisted Pair
  • CAT3 or CAT5 – difference the two has to do with the tightness of the copper wires that were wound
  • Tightness determines its resistance to interference
  • CAT3 is older and cable length is a common failure
• Fiber Optic
  • Immune to EMI
  • Longer usable length – up to 2kms
  • Expensive

Technology Failures

Ethernet

• Most popular
• Extremely resistant to failure, especially in a star-wired configuration

Token Ring

• Since token is passed by every station on the ring, NIC set at wrong speed or in error state can bring the network down

FDDI – Fiber Distributed Data Interface

• Dual rings fault tolerance (if first ring fails, the secondary ring takes over)
• Sometimes uses second ring for improved performance

Leased Lines

• T1 and ISDN – go with multiple vendors to reduce failures

Frame Relay

• Public switched WAN
• Highly fault tolerant
• Bad segments diverts packets
• Can use multiple vendors for high availability

Other Single Points of Failure

• Can be any device where all traffic goes through a single device – Router, firewall, hub or switch
• Power failure – surges, spikes (need for UPS)