Sql Server AlwaysOn

Question 1

What is called as Level of Availability?

Answer 1

The amount of time that a solution is available to end users is known as the level of availability, or uptime. To provide a true picture of uptime, a company should measure the availability of a solution from a user’s desktop. In other words, even if your SQL Server has been running uninterrupted for over a month, users may still experience outages to their solution caused by other factor

the level of availability is often referred to in 9s. For example, five 9s of availability means 99.999 percent uptime and three 9s means 99.9 percent uptime.

Question 2

What does five nines of availability means?

Answer 2

the level of availability is often referred to in 9s. For example, five 9s of availability means 99.999 percent uptime and three 9s means 99.9 percent uptime.

Question 3

What is SLA and SLO?

Answer 3

When a third-party provider is responsible for managing servers, the contract usually includes service-level agreements (SLAs). These SLAs define many parameters, including how much downtime is acceptable, the maximum length of time a server can be down in the event of failure, and how much data loss is acceptable if failure occurs. Normally, there are financial penalties for the provider if these SLAs are not met. In the event that servers are managed in-house, DBAs still have the concept of customers. These are usually the end users of the application, with the primary contact being the business owner. An application’s business owner is the stakeholder within the business who commissioned the application and who is responsible for signing off on funding enhancements, among other things. In an in-house scenario, it is still possible to define SLAs, and in such a case, the IT Infrastructure or Platform departments may be liable for charge-back to the business teams if these SLAs are not being met. However, in internal scenarios, it is much more common for IT departments to negotiate service-level objectives (SLOs) with the business teams, as opposed to SLAs. SLOs are very similar in nature to SLAs, but their use implies that the business do not impose financial penalties on the IT department in the event that they are not met.

Question 4

What is RPO and RTO?

Answer 4

The recovery point objective (RPO) of an application indicates how much data loss is acceptable in the event of a failure. For a data warehouse that supports a reporting application, for example, this may be an extended period, such as 24 hours, given that it may only be updated once per day by an ETL process and all other activity is read-only reporting. For highly transactional systems, however, such as an OLTP database supporting trading platforms or web applications, the RPO will be zero. An RPO of zero means that no data loss is acceptable.

The recovery time objective (RTO) for an application specifies the maximum amount of time an application can be down before recovery is complete and users can reconnect.

Question 5

What are the classes of standby servers? What are their description and examples?

Answer 5

There are three classes of standby servers

1) Hot
2) Warm and
3) Cold

Hot: A synchronized solution where failover can occur automatically or manually. Often used for high availability.

Examples: Clustering, AlwaysOn Availability Groups (Synchronous)

Warm: A synchronized solution where failover can only occur manually. Often used for disaster recovery.

Exanples:Log Shipping, AlwaysOn Availability Groups (Asynchronous)

Cold: An unsynchronized solution where failover can only occur manually. This is only suitable for read-only data, which is never modified.

Examples: na

Cold standby does not show an example technology because no synchronization is required and, thus, no technology implementation is required.