IT Infrastructure and Availability Concepts

Availability Concepts

• Availability measures how consistently a system is operational and accessible.
• It's the ability of a system to perform its required functions at a given moment or over a defined period.

High Availability (HA)

• High availability (HA) is crucial in IT infrastructure to prevent disruptions, financial losses, and customer dissatisfaction.
• The key goal in IT infrastructure is to ensure consistent access to resources and services.

Calculating Availability

• Availability cannot be calculated or guaranteed upfront.
• It's only reported after a system has been running for some time.
• Over time, significant knowledge and experience are gained on how to design highly available systems.

Availability Percentage per Time

• Availability is commonly expressed as a percentage of uptime within a given time period (e.g., yearly or monthly).
• Different percentages represent varying levels of downtime.
• 99.8% availability = 86.2 minutes downtime per month.
• 99.9% availability = 43.2 minutes downtime per month
• 99.99% availability = 25.9 seconds downtime per month

Service Level Agreements (SLAs)

• Typical service level agreements (SLAs) specify 99.8% or 99.9% availability per month for an entire IT system.
• Infrastructure availability is typically higher, usually in the range of 99.99% or higher.

Unavailability

• Defining the maximum frequency of unavailability is good practice.
• Acceptable levels of downtime (in minutes) are directly correlated with the number of events that can occur annually.

Mean Time Between Failures (MTBF) and Mean Time To Repair (MTTR)

• Mean Time Between Failures (MTBF) represents the average time between failures of a component.
• Mean Time To Repair (MTTR) is the time taken to recover from a failure.

MTBF and Component Examples

• Some components have higher MTBFs than others.
• Examples and MTBFs (in hours):
  • Hard disk: 750,000 hours
  • Power supply: 100,000 hours
  • Fan: 100,000 hours
  • Ethernet Network Switch: 350,000 hours
  • RAM: 1,000,000 hours

MTTR Reduction Strategies

• Keeping MTTR low can be achieved by:
• Service contracts with suppliers
• Having on-site spare parts
• Implementing automated redundancy and failover

Steps for Repair

• Steps for completing repairs include:
  • Fault notification (before alarm message)
  • Alarm processing
  • Identifying the root cause of the error
  • Locating repair information
  • Obtaining spare components
  • On-site technician repair
  • System reboot and testing

Calculating Availability from MTBF and MTTR

• Availability calculations can be determined using the MTBF and MTTR calculations.
• Tables provide a few concrete examples, showing the relationship between availability percentages and their correlated downtime figures.

Serial and Parallel Components

• Serial components; failures in one part lead to system-wide downtime.
• Parallel components; some failures do not impact availability (e.g., having multiple power supplies).

Sources of Unavailability (Human Errors)

• Human errors account for 80% of outages that impact critical systems.
• Examples of human errors include:
  • Performing tests in production environments
  • Repairing the wrong components
  • Misplacing backups
  • Accidentally removing files

Sources of Unavailability (Software Bugs)

• Application and Operating System bugs can lead to entire system failures.
• Software complexity makes bug-free systems nearly impossible to achieve.

Sources of Unavailability (Planned Maintenance)

• Planned maintenance is sometimes necessary but can create vulnerabilities to system downtime.
• Backup and upgrade tasks often lead to temporary Single Points of Failure (SPOF).

Sources of Unavailability (Physical Defects)

• Mechanical parts are more prone to failure than software or human errors.
• Examples include failing cooling equipment fans, disk drives, and tape drives.

Sources of Unavailability (Bathtub Curve)

• Component failure rates are highest when new.
• After initial use, failures typically decrease until reaching a steady-state level.

Sources of Unavailability (Environmental Issues)

• Environmental problems can disrupt systems.
• Power failures, cooling issues, and natural disasters (fires, earthquakes, floods).

Sources of Unavailability (Infrastructure Complexity)

• Adding components to complex systems often creates more points of potential failure.
• Design complexity makes maintenance and repair much harder to implement.

Redundancy

• Redundancy involves duplicating critical components to prevent single points of failure (SPOF).
• Examples include having multiple power supplies, dual network interfaces, and redundant cabling.

Backup Components and Options

• Backup components (hardware/software) are activated when primary components fail.
• Software backups and failover options improve system resilience by minimizing single points of failure.

Reliability

• Reliability is a system's ability to perform as expected consistently.
• Hardware/software quality, regular maintenance, and error monitoring support reliability and availability.

Maintainability

• Maintaining effective maintainability allows easier repair, upgrades, and reduced downtime within a system.

Fault Tolerance

• Fault tolerance is a system's capacity to continue operation despite hardware or software failures.
• Examples include RAID systems, which continue to function even if some drives fail.

Fallback

• Fallback is the manual switching to an identical standby system in a different location when a main one becomes unavailable due to a disaster or crisis.
• Three types exist; hot sites, warm sites, and cool sites, with hot sites being the most expensive but offering the quickest return to service when compared with warm sites and cool sites.

Failover

• Failover is the automatic switching to a standby system or component when the primary one fails.
• Several examples exist within Windows, VMware, and Oracle.

Failover Mechanisms

• Automatic failover instantaneously redirects traffic without user input.
• Manual failover requires user initiation.

Load Balancing

• Load balancing distributes network traffic across multiple servers.
• Examples of load balancing methods include Round Robin and Dynamic load balancing.

Clustering

• Clusters group interconnected systems to work together as a single unit.
• High availability clusters limit downtime, whereas load-balancing clusters enhance performance by distributing tasks across systems.

Data Backup and Recovery

• Regular data backups are critical for restoring data in the event of system failures, cyberattacks, or other problems.
• Backup types include full backups and incremental backups.

Disaster Recovery Planning

• Disaster recovery planning (DRP) outlines a strategy for restoring systems and data after a disaster.
• Critical components include backup resources, communication plans, and designated recovery sites.

Monitoring and Management

• Monitoring and management tools identify potential issues before downtime occurs.
• Examples include Nagios and Splunk.
• Proactive management involves regular system checks to reduce failure rates.

Complexity of Infrastructure

• Complex infrastructure often leads to more points of potential failure.
• Managing high availability requires effective methods for handling complexities in an IT environment.

Factors Adding Complexity

• Multiple systems lead to management complexities
• Applications' compatibility or integration issues are challenges that require attention and careful management.
• Geographical differences add latency issues to IT systems, requiring careful handling by the IT management team.

Managing Complexity

• Standardizing processes, implementing automation, and enhancing routine task management are ways to manage complexity.

Balancing Complexity with Availability

• Complex systems require careful design and effective practices to avoid issues that affect Availability.
• Methods include consolidating systems, streamlining processes, and implementing robust monitoring solutions.

Business Continuity

• Business continuity is the ability to continue operations during disasters or disruptions.
• Defining and developing a DRP is a way to manage Business Continuity effectively.

RTO and RPO

• Recovery Time Objective (RTO) is the maximum allowed time to restore a business process after a disaster.
• Recovery Point Objective (RPO) is the maximum acceptable data loss after a disaster.

This quiz explores the concepts of availability in IT infrastructure, focusing on how consistently systems are operational. It covers topics such as high availability, the calculation of availability, and the significance of uptime percentages. Test your understanding of these critical IT principles and ensure you grasp the importance of reliable system performance.