2.5 Step 4: Defining mission-critical service-level agreements


One final key to providing continuous availability for your Exchange deployment is the ability to set some guidelines for determining whether the system is meeting the organization’s business objectives for implementing the system in the first place. E-mail has become a key mission-critical application within most organizations, but just how much service degradation can the organization tolerate before the messaging system becomes a hindrance instead of a business advantage? The means of translating business objectives and requirements for any system is usually provided in the form of SLAs. SLAs come in various forms and can be established for every facet of system function and operation. For an Exchange deployment, SLAs help management determine whether the system is delivering the services that the organization desired when investing in the system in the first place. SLAs also assist system managers in ensuring that the business services they have committed to are being delivered. SLAs come in many forms and can touch many areas of operation for an Exchange deployment. Table 2.3 shows the types of SLAs that can be established for message systems. Table 2.4 highlights some common SLAs that are used for messaging systems to ensure optimal functionality and maximum availability.

Table 2.3: Service-Level Agreement Types

SLA Type

Description

Performance SLA

Established to measure how the system performs and to provide an acceptable user experience. Examples include message delivery, response time, replication periods, message rates, bytes rates, and so forth.

Recovery SLA

Established to provide guidelines for maximum tolerable downtime. Can be set for server, mailbox, or even message recovery. Also may measure system failover times. Can also be used to drive or set recovery windows to disaster-recovery operations.

Security SLA

Established to provide goals for ensuring system security. Can focus on intruder detection, viral and denial-of-service detection and attacks, or encryption and other secure service performance.

Management or Administrative SLA

Established to measure administrative and management activities such as user maintenance and account service. May include service timeouts or response time guidelines.

Table 2.4: Service-Level Agreement Examples

SLA

Description

Example

Message delivery time

Established on a site and/or organizational basis to ensure that message delivery does not exceed limits set by business requirements

95% of messages delivered within 10 minutes (global); 99% of messages delivered within 30 minutes (global)

Message rate

Sets a message delivery or transaction rate for the messaging system

100 message open/second; 50 messages sent/second

Information store recovery SLA

Maximum tolerable time that a database can be off-line

4-hour SLA

Individual mailbox SLA

Maximum tolerable time that a mailbox can be unavailable; also could be a recovery target SLA

1 hour

Gateway throughput SLA

Sets a target SLA for an SMTP or X.400 gateway in terms of messages per hour, day, and so forth

1,000,000 messages/day; 1 GB/ hour

Virus detection SLA

Sets a guideline for detecting and eliminating viruses

99% viral-detection rate

Replication SLA

Sets a guideline for ensuring replication activities such as public-folder replication, free/busy, and so forth

24-hour replication worldwide

Client service SLA

Target for client service availability

< 100 lost opportunities per 1,000,000 operational hours

Server availability SLA

Target for messaging server uptime per measured period

99.99% availability

SLAs are the only means we have of ensuring that the messaging system is delivering business value to the organization. Without SLAs it is difficult to provide consistent functionality and service availability. Also, system managers have no criteria on which to base staffing, procedures, and training. The obvious goal should be to provide messaging services as close to 100% of the time as possible. However, uptime is not the only focus of SLAs. We can also use SLAs to provide a high degree of user experience and functionality by setting SLAs for performance, recovery, and administration. SLAs are an essential part of helping to define your operational procedures for your system. SLAs tie closely to proactive management and administration techniques and practices. We will discuss SLAs in more detail in Chapter 10.




Mission-Critical Microsoft Exchange 2003. Designing and Building Reliable Exchange Servers
Mission-Critical Microsoft Exchange 2003: Designing and Building Reliable Exchange Servers (HP Technologies)
ISBN: 155558294X
EAN: 2147483647
Year: 2003
Pages: 91
Authors: Jerry Cochran

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