1. Introduction to High Availability
H6487S I.02
Module 1

2. What Causes a System to Go Down?Up
Planned
Unplanned
Down
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3. © 2003 Hewlett-Packard Development Company, L.P.
Causes of Failures
Application Failure
Hardware
20%
40%
40%
IT Processes
Operator Errors
Source: Gartner Group
October 1999
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4. Not a Big Deal? You Tell Me!
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5. Average Cost per Hour of Downtime
Financial - Brokerage Operations
$6.45 Million
Financial - Credit Card Sales
$2.6 Million
Media - Pay per view
Retail - Home
Shopping (TV)
Retail - Home
Catalog Sales
Transportation
Airline reservation
Media
Teleticket sales
Transportation - Package shipping
Finance - ATM fees
$100,000
$200,000
$300,000
Millions
Source: Dataquest Perspective, Sept. 1996
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6. What Is High Availability?
3/14/2018
What Is High Availability?
A system is highly available if a single component or resource
failure interrupts the system for only a brief time.
What is a system? (Computer? Network? Application?)
What is a resource? (Hardware? Software? OS? Database?)
What is a failure? (Disk crash? Too many packets? Full file system?)
What is an interruption? (Reboot? User reconnect? Poor performance?)
What is a brief time? (Minutes? Hours? Days?)
HIGH AVAILABILITY IS A DESIGN!
Depends on the
viewpoint
This definition of High Availability (HA) is very general and requires the expansion of the terms: system, resource, failure, interrupts and brief. These will vary depending on the viewpoint taken. For example system and resource tend to mean ‘hardware’ to an administrator. To an application user however, the ‘killing’ of a database process is a failure resulting in loss of availability of a ‘soft’ resource.
The ‘system’ is more than the hardware, and includes the operating system, application processes, data AND the ability of users to connect to and use the resources.
Some failures can be handled transparently without any interruption (eg. disk failure in a RAID array, single bit memory error) others can result in complete loss of service and a restart. The priority of an HA system is to minimise the the duration of the interruption ( typically tens of minutes) and by design reduce it to zero for many types of failure.
The focus is TIME.
It should be noted that a well designed HA configuration can also provide an excellent control environment for applications, helping to reduce interruptions to service from system upgrades and backups.
H6487S I.02
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7. Computer System Availability
System: Computer
Resources: CPU Memory Disk
Failures: System crash Disk failure
Interruption: System reboots Replace failed hardware
Outage Time: Minutes to days
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8. © 2003 Hewlett-Packard Development Company, L.P.
Network Availability
System: Network
Resources: Computers, routers, hubs, LAN cables, backbone, Modems, phone lines
Failures: Failed network hardware, Bad cables, High packet collision rate
Interruption: Slow user response, User reconnects, Replace failed hardware
Outage Time: Minutes to days
H6487S I.02
© 2003 Hewlett-Packard Development Company, L.P.

9. Application Availability
System: Application
Resources: Computers, networks, operating system resources
Failures: System crash, Network component failure, Full file system, performance paralysis
Interruption: Slow response time, system reboots, Replace failed hardware
Outage Time: Minutes to days
H6487S I.02
© 2003 Hewlett-Packard Development Company, L.P.

10. Three Pillars of High Availability
High Availability Alliances
High Availability Alliances
Support Partnerships
IT Processes
& People
Support Partnerships
IT Processes
and People
Technology Infrastructure
Technology Infrastructure
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11. 5nines Support Partnerships
H6487S I.02
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12. High Availability Terms
Downtime
Unplanned
Outage
Availability
Fault Tolerant
H6487S I.02
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13. High Availability Percentages
99.999
99.99
99.95
99.90
99.86
99.73
99.00 98 97 96 95
Total Down Time
5 minutes
50 minutes
4.3 hours
8.8 hours
12 hours
24 hours
3.6 days
7.2 days
10.8 days
14.4 days
18 days
Type of System
Fault Tolerant
Top High Availability
Median High Avail
HP Standard Avail
Most Standard Avail
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14. Availability Continuum Hierarchy
Cost $$
continuously
available
systems
highly
available
systems
highly
resilient
reliable
systems
systems
Availability
H6487S I.02
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