Chapter 5 - CIS Home Page

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					Chapter 5: Server Hardware and
          Availability
  Hardware Reliability and LAN
• The more reliable a component, the more expensive it is.

• Server hardware is more expensive than desktop workstation
  hardware as it needs to be more reliable.

• If a workstation fails, one person is inconvenienced. If a
  server fails, many people are inconvenienced.

• Servers need to be as powerful as possible as many people can
  be using them at once.
               Hot Swappable
• A hot swappable device is one which can be replaced whilst
  the server is still in operation.

• You should only hot swap components when the component
  and operating system supports it.

• The following components can be hot swapped: RAM, disk
  drive, power supply, NIC, graphics cards.

• Hot swappable components are more expensive. Often only
  necessary when you need to keep a server operational 24/7.

• Most organizations can tolerate a server being offline after
  hours for maintenance.
      Multiple Power Supplies
• Multiple power supplies can allow a server to function after
  one power supply fails.

• Power supplies are the component most likely to fail in a
  server. They are also one of the cheapest components.

• Having multiple power supplies doesn’t mean you can hot
  swap. In many cases it will allow you to keep your server
  running until you can choose the right time to power down
  and replace the failed component.
                        UPS
• Stands for Uninterruptible Power Supply.

• A battery that allows a server to remain functional when there
  is a loss of mains electricity.

• Battery also used when power fluctuates to provide a stable
  current to the server. Brownouts occur more often than
  blackouts and can do just as much damage.

• Most operating systems can be configured to gracefully shut
  down once the server shifts to battery power.
  Asymmetric Multiprocessing
• Where special processors can be delegated specific tasks
  by the operating system.

• Graphics cards are an example. Graphics processing occurs
  on the graphics card’s processor rather than the computer’s
  CPU.
   Symmetric Multiprocessing
• Symmetric multiprocessing involves having several
  processors of the same make and model working in parallel.

• Tasks are balanced across all processors.

• Operating system assigns tasks to processors based on current
  processor load.
           CISC and RISC CPU
CISC: Complex Instruction Set Computer
RISC: Reduced Instruction Set Computer

CISC CPU: Intel Pentium – Pentium IV. AMD K6
RISC CPU: UltraSPARC III, PowerPC G3-G5

• RISC CPU have a smaller and more highly optimized processor
  instruction set than a CISC CPU.

• RISC design came about because a study found that 80-90% of
  instructions were not used when computer code was compiled. Prior
  to the 1980s, when it was more common to write code in assembly
  language, most of a CPU instruction set was used.

• The most common instructions are processed more quickly on
  RISC. Less common instructions are processed more quickly on
  CISC.
   Operating Systems and CPU

Microsoft Windows Server 2003 supports Intel and AMD
CISC CPU. Although Windows NT4 supported PowerPC as
well.

Apple OSX supports PowerPC only.

Sun Solaris supports UltraSPARC only.

Linux supports all processor architectures.
              RAID Overview
• Stands for Redundant Array of Inexpensive Disks.

• RAID is a way of using multiple disk drives and controllers to
  increase read/write speed or redundancy.

• Hardware RAID is controlled by special hardware.
  Operating system is unaware of special disk configuration.

• Software RAID is controlled by operating system. Less
  expensive than Hardware RAID, but often slower.

• Appears as a single volume to the operating system.
  RAID 0
                                        Three disk RAID 0
                                        Each stack is a separate disk.
Disk Striping without Parity            Each color a different file.


• Does not offer redundancy, does offer read/write improvement.

• Different parts of the file are written to different disks at the same
  time.

• This significantly improves write time. The more disks in the
  RAID 0 array, the faster it is.

• Drawback is that if one disk in RAID 0 array fails, all array data is
  lost.
                       RAID 1
                                                 RAID 1. 2nd disk is
Disk Mirroring and Duplexing                     exact copy of first.


Disk mirroring: two disks, one controller
Disk duplexing: two disks, two controllers

• Duplexing is more fault tolerant than mirroring as failure of the
 controller in mirroring will mean loss of the volume.

• All data on the first disk is mirrored on the second disk.

• Data written to one disk is automatically written to the second.
                       RAID 1
                                                RAID 1. 2nd disk is
                                                exact copy of first.


• Data deleted from the first disk is automatically deleted from the
  second.

• When one disk fails, the other continues operating without loss of
  data. With hot swappable drives, you could then replace the failed
  disk and the RAID 1 volume would automatically recreate the
  mirror.

• Expensive because it requires twice the physical disk storage space.
  A 1000 GB RAID 1 volume made from 200 GB disks would
  require 10 disks.
              RAID 5
Disk Striping with Parity
                                                   Parity
                                                   Data
• Minimum of 3 disks

• Parity information is shared across all disks. In the event one disk
  fails, data can be recovered to a new disk using the parity
  information stored on the other disks on the set.

• Faster than RAID 1 as data is read and written from multiple disks
  at the same time.

• Slower than RAID 0 as parity information must be generated and
  written.

• Requires one extra physical disk. A 1000 GB RAID 5 volume made
  out of 200 GB disks would require 6 disks.
           RAID 1+0 and 0+1
          RAID 0                    Stripe              RAID 1
                                    Data
RAID 1    RAID 1    RAID 1          Mirror   RAID 0              RAID 0




         RAID 1+0                                     RAID 0+1


• Combines striping with mirroring and requires a minimum of 4
  disks.

• RAID 1+0 (also known as RAID10). Multiple mirrored pairs
  combined into stripe sets.

• RAID 0+1. Stripe sets that are mirrored.
           RAID 1+0 and 0+1
          RAID 0                    Stripe                 RAID 1
                                     Data
RAID 1    RAID 1    RAID 1          Mirror      RAID 0              RAID 0




         RAID 1+0                                        RAID 0+1

• RAID 1+0: Better fault tolerance. In some cases can still function
  if multiple disks fail.

• RAID 0+1: Better performance. If single disk fails, becomes a
  RAID 0 set.

• Expensive because it requires twice the physical disk storage
  space. A 1000 GB RAID 1+0 volume made from 200 GB disks
  would require 10 disks.
       Active/Active Clustering
• Uses a shared data source, either
  fibre channel or NAS.

• All servers in cluster operational
                                                         Shared storage
  at the same time.

• Cluster appears as single server to devices on network.

• Servers that make up cluster known as nodes.

• Jobs allocated to server are distributed between nodes.

• If node fails, other nodes in cluster take up slack.
     Active/Passive Clustering
 Active node                                Passive node




                      Shared storage

• Uses shared storage.

• One node is active, the other in a “stand by” state.

• Stand by node becomes active when an active node fails.

• Can be combined with active/active clustering.
      Network Load Balancing
• No shared storage.

• Useful when data is not updated frequently (such as Web
  sites).

• NLB software monitors load on each server. Server with
  lightest load receives the next job.

• If node fails, NLB cluster is reconfigured automatically and
  jobs are reassigned.

• If node added, NLB cluster is
  reconfigured automatically.
              Round Robin DNS
• Basic clustering solution.

• IP address of host nodes entered in DNS.

10.0.0.1       A       cluster.companyname.com
10.0.0.2       A       cluster.companyname.com
10.0.0.3       A       cluster.companyname.com
10.0.0.4       A       cluster.companyname.com

• DNS returns different IP address each time host name is
  queried.

• Does not ensure that load is balanced, just that each server
  receives the same number of new queries.
                    Summary
• Network servers are the most important computers on the
  LAN and need to be the most reliable.

• Hot swappable devices can be replaced when the server is in
  operation.

• Multiple power supplies can keep a server running in the
  event that one fails.

• UPS allows a server to run on battery power if the need arises.
                    Summary
• Symmetric multiprocessing allows processing tasks to be
  shared across more than identical processor.

• Active/active clustering has shared storage and shares jobs
  between nodes. Appears as a single server to clients.

• Active/passive clustering has a server on standby. If a node
  fails, the stand by server comes online.
         Discussion Questions
 Explain the difference between active/active clustering and
  active/passive clustering?

 Describe the difference between NLB and Round Robin
  DNS?

 Describe the benefits/drawbacks of RAID 5 compared to
  RAID 1+0.

 What is a hot swappable component?

 Why do servers need to be so reliable?

				
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