CISSP Exam Note (Domain 2: Telecommunications and Networking Security) – Availability Concepts / Fault Tolerance

December 1, 2009 · Posted in Information Security, Information Systems 

Availability means that the information, the computing systems used to process the information, and the security controls used to protect the information are all available and functioning correctly when the information is needed. The opposite of availability is the lack thereof, one example of this is a common attack known as a denial of service (DoS) attack.

For example: In 2000 Amazon, CNN, eBay, and Yahoo! were victims of a DoS attack.

“ Yahoo Attacked. No one knows what happened except that it was inaccesable for more than 3 hours. It was also known that the attack was co-ordinated and hence the standard firewall algorithms failed to figure out what was happening.

Source: http://en.wikipedia.org/wiki/Information_assurance

Fault Tolerance is the ability of a system to respond gracefully to an unexpected hardware or software failure. There are many levels of fault tolerance, the lowest being the ability to continue operation in the event of a power failure. Many fault-tolerant computer systems mirror all operations — that is, every operation is performed on two or more duplicate systems, so if one fails the other can take over. Source: http://www.webopedia.com/term/f/fault_tolerance.html

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Network Availability

  • RAID – Redundant Array of Inexpensive Disks
  • Back-up Concepts
  • Manage Single Point of Failure

RAID – Redundant Array of Inexpensive Disks

  • Fault tolerance against server crashes
  • Secondary – improve system performance
  • Striping – caching and distributing on multiple disks
  • RAID – employs the technique of striping, which involves partitioning each drive’s storage space into units ranging from a sector (512 bytes) up to several megabytes. The stripes of all disks are interleaved and addressed in order
  • Hardware and software implementation

RAID Advisory Board

  • Three types
    • Failure Resistant Disk Systems (FRDS) – the only current standard;
    • Failure Tolerant Disk Systems;
    • Disaster Tolerant Disk Systems
  • FRDS
    • Provides the ability to reconstruct the contents of a failed disk onto a replacement disk
    • Enables continuous monitoring of these parts and the alerting of their failure
  • FRDS+
    • Protect from disk failure – can reconstruct disks by automatically hot swapping while server is running
    • Includes environmental controls
    • FRDS+ adds hazard warning

RAID Levels

RAID 0 – Striping

  • Creates one large disk by using multiple disks – striping
  • No redundancy
  • No fault tolerance (1 fail = all fail)
  • Read/write performance is increased

RAID 1 – Mirroring

  • Duplicates data on other disks (usually a one to one ratio)
  • Expensive (doubles cost of storage)

RAID 2 – Hamming Code Parity

  • Multiple disks
  • Parity information created using a hamming code
  • Can be used in 39 disk array 32 data and 7 recovery
  • Not used, replaced by more flexible levels

RAID 3 – Byte Level Parity / RAID 4 – Block Level Parity

  • Stripe across multiple drives
  • Parity information on a parity drive
  • Provides redundancy
  • Can effect performance with a single parity drive

RAID 5 – Interleave Parity

  • Most popular
  • Stripes data and parity information across all drives
  • Uses interleave parity
  • Reads and writes performed concurrently
  • Usually 3-5 drives – if one drive fails, can reconstruct the failed drive by using the information from the other 2

RAID 7 – Single Virtual Disk

  • Functions as a single virtual disk
  • Usually software over Level 5 hardware
  • Enables the drive array to continue to operate if any disk or any path to any disk fails

RAID Summary

  • 0 – Striping
  • 1 – Mirroring
  • 2 – Hamming Code Parity
  • 3 – Byte level parity
  • 4 – Block level parity
  • 5 – Interleave parity
  • 7 – Single Virtual Disk

Other Types of Fault Tolerance

Redundant Servers

  • Primary Server mirrors to secondary server
  • Fail-over or rollover to secondary in the event of a failure
  • Server fault tolerance can be warm or hot

Server Cluster

  • Group of independent servers managed as a single system
  • Load balancing
  • Improves performance
  • “Server Farm”
  • Microsoft Cluster Server
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