What is a Database Cluster?

If it seems like you have a bunch of messy files and you have no idea about what step to take next, then you need to consider getting a database. The database will help you in storing and managing your files with the use of various commands such as SQL statements. With the use of the database, you’ll be able to organize your files according to clusters. This is called “database clustering”. How is database clustering relevant to the database management system?

The database cluster is a program in a database management system that provides users the opportunity to share or keep the files exclusive to themselves. The database cluster, particularly the SQL cluster, was developed in 2004 and was an added feature to the SQL database management system. Database cluster is designed for high-level performance, and users can ensure that this program has a linear scalability.

What is a Database Cluster? database cluster

Know the Features of a Database Cluster

A database cluster has several features that will both give you some advantages and disadvantages. The database cluster has the ability to replicate any shared data. The database cluster utilizes a synchronous replication that allows the data to be copied in multiple nodes upon writing the data. In a database cluster replication, the two copies or replicas can be stored either one at a time or at the same time. The database cluster also has the ability to store data in partitions. This is called the “horizontal data partitioning”. With the database cluster, all data will automatically be stored in several data nodes with the system. The database cluster can also be stored either in the disk or in memory. This is called “hybrid storage”. The data are then stored in memory, while the data is written in the disk asynchronously. This is because of the database cluster’s ability to replicate. In the event when all installations of hardware and software are perfectly in place, the database cluster will not need any shared disk because there are definitely no room for errors and failures.

How to Create a Database Cluster

Before doing anything, you must first create a database cluster or database storage on disk. A database cluster is a collection of databases within a database management system. After initiating the database cluster, the database will be named. For instance, the database is named Template 1. This means that this database will only be used for a created database and, thus, cannot be used for actual work. In the database system, the database cluster can be identified as the data directory, so users can definitely store data anytime, anywhere. But if you want to make a database cluster area, then here are the instructions you should specifically follow:

1. You will initially log in as a root.

2. Create a directory which will act as your database cluster area. Then you should reassign the ownership to the Postgre account, which comes with the database software. For instance, you can use this command – root# mkdir /var/lib/pgsql/data, root# chown postgres /var/lib/pgsql/data.

3. You can log on to your Postgre user account.

In order to start your database cluster, you should place the command, “initdb”. Since the database cluster includes all the files in the database, you’ll need to secure it. The initdb command will therefore restrict unauthorized persons who want to access your data.

What is High Availability?

In IT terms, high availability is the term used to describe a server or network, and by extension all of the constituent components, that is continuously available for data input, processing, and report querying. In it’s simplest sense, we see high availability in our everyday interactions on the web, it is very rare for the top 10 websites to be offline.

The systems and protocols in place largely determine the success or not of a high availability goal, mostly because components fail randomly, and no group of components is ever going to be failsafe, so ensuring continuous supply of service is dependent on planning and understanding the tolerances that affect the network.

Twenty-first century society is so dependent on computers and their processing power that anything less reliable and permanent uptime is considered a failing, corporations thrive or fail on their network or service uptime reputation.

What is High Availability? datacenter

Even at the small corporation and private individual level, high availability may still be necessary and desirable. Our dependence on timely email, online banking and financial trades, upto date weather and news, are all examples of services that require high availability, failing to deliver only ever benefits the competition in a free market.

Fault tolerance is an important measure of any high availability system or network, essentially a single failure point should never bring the entire system down, an alternate component should be able to transparently take over the task until the original is replaced or repaired.

Reliable components with long lives and capable of sustaining extensive periods without maintenance also form an important aspect of high availability networks. Typically these components are not the cheapest models in the market, increased reliability is a factor of how well designed and made a component is, and higher quality standards come with a price.

Measuring reliability is often considered in terms of an uptime percentage, certainly most telecommunications and web hosting corporations advertise uptime guarantees of 99 or higher percent. Mission critical availability of servers, and networking systems is often described in terms of 99.999% uptime, equating to just 5.26 minutes of downtime per month.

In fact, this measure is not easily quantified and is subject to interpretation, a server that is up may not be available to the end user, for example when an outage occurs on some other part of the network, or where a software glitch prevents the user from completing their task.

Creating a high availability system will involve extensive planning, with the goal being to make the entire system as simple as possible, with the least number of potential failure points. Overly complex systems typically have more failure points that need to be accounted for, increasing cost, complexity, and monitoring. By contrast simpler systems are easier to monitor, and despite using more expensive and more reliable components are often cheaper to build in the long run.

Testing high availability networks at their failure points should be conducted regularly, however backup systems or redundant components also require testing, thus ensuring the entire network remains available in the event of component failure or disaster.

What are High Availability Servers?

High availability servers a modern implementation of server hardware that are designed to extremely high fault tolerance levels to keep performing even in the event of a failed component, and are the latest buzzword in server technology with major CPU designers hailing the technology as the next evolutionary step.

Traditionally, server hardware and software have been designed to optimize the functions of a single CPU controlling memory, storage, and input/output, leading to never satisfactory multitasking that has to a great extent been dependent on operating system software juggling processes within the CPU. This method gives the illusion of multitasking, but is more accurately described as task switching rather than multitasking.

Current designs of high availability servers known as shared memory mulitprocessors (SMP) offer increasing numbers of single processors in a single server, and making use of larger banks of shared memory, allowing for scalable allocation of tasks and consequently faster processing. Ultimately SMPs are designed for more reliable service and better uptime.

Advances in hot swap technology are actively used within high availability servers and is now used not just in USB accessories, but also in hard drives, memory, video cards, even some CPUs, allowing for online spares to be provisioned. The ability of a server to continue functioning thru intelligent allocation based on the number of working components within the server is a major development offering greater than average up-times.

What are High Availability Servers? High Availability

A component that fails is intelligently ignored until IT has the chance to replace the component. In combination with RAID storage and larger memory blocks, modern servers are evolving from single computers into mini networks and can competently be used in smaller storage area networks with a reduced overall number of servers.

Using high availability servers in this manner also allows for more robust server mirroring and clustering that is internally optimized with it’s own redundancies built in, reducing the need for costly backup networks, and making outsourced disaster recovery data centers a very attractive option despite limits to network speed that make offsite backup less appealing.

As the technology improves, software vendors are anticipating huge demand for new generations of server management software that not only manages a single multiprocessor server, but is also able to manage data across smaller more powerful clustered networks.

Particularly important in high availability server clusters is proper configuration of server load balancing, a technique where two or more servers are able to process similar tasks but accessing the same database, thus allowing for more users concurrently. It seems moot to suggest load balancing needs to be considered, yet many administrators don’t tune their networks for optimal balancing leading to slower performance and potential glitches.

Maintaining high availability servers requires up to date and specialist knowledge of the tools and technologies used to ensure operating platforms are more secure against attack and resilient against failure. Staff employed in this important function should be certified by one of the major vendors as having been tested and found to pass the relevant examiniations.

What are High Availability Clusters

High availability clusters (HA clusters), also known as failover clusters, are a network of servers configured to operate as a single machine with data backups occurring in real time so that in the event of a failure in the network backup machines will take over seamlessly and continue to operate. High availability clusters are designed to operate automatically and not need the intervention of an IT support person to restart the network.

A single server that fails results in downtime of the network, in some organizations this can be measured in days or weeks and threatens business continuity. Even short period downtime of critical servers can in some instances result in significant losses of income. Building fault tolerant servers with redundant power supplies, duplicated components, and RAID storage offers some protection of data and improved uptime, yet still offers only a single CPU and if that fails so too will the server.

By contrast, high availability clustered servers are setup with intelligent software that monitors all servers within the cluster for problems, and are designed to keep going regardless of component failures. In business critical situations downtime is costly both in terms of revenue and customer trust, and in extreme situations such as hospitals may even be life threatening.

What are High Availability Clusters High Availability Clusters

Very few Fortune 500 companies and other major corporations operate without high availability clusters. Each node in the cluster has the capability to take over from another, so even though some servers are properly setup as backup servers ready to assume primary server roles, the same could be said in reverse. Clustered backup servers are therefore never configured in a cold or warm state, they are in fact always hot, with real time synchronization occurring.

Enhancing a clustered server setup for even more redundancy usually requires setting up geographically disparate data centers with very high speed network connections, that are synchronized the same way, although the hope is that a major disaster affecting the corporation won’t shut down the network.

Multiple site high availability clusters are more expensive to setup, and more difficult to configure, but once the network is operational maintenance is routine. Servers are connected using multiple links from different carriers ensuring further redundancy. Typically data centers are chosen that don’t share the same risks of disaster, so a data center in California that could be affected by earthquake might be mirrored with a center in Chicago that would not be affected.

High availability clustering design is technically demanding and complex, and can be quite tricky to configure to ensure load balancing is equally matched across all servers. Seamless load balancing of some tasks such as serving web pages can be accomplished quite easily, but is less easy with transactional tasks or read/write services unless disk mirroring is very close to real time and sessions can be shared across servers.

Software for running a high availability cluster is readily available, however applications will need to be tested for robustness, particularly it’s handling of data in the event of a crash and use of non-volatile storage in preference to shared storage.

High Availability Architecture

High availability networks are complex and costly systems to rollout with long planning timeframes  and high expectations from users that the system will perform. To choose the correct hardware and software and the optimum network design IT administrators and their staff invest a considerable amount of time in analysis of corporate needs. Network architecture that is rated high availability needs to perform to very strict standards of uptime.

Redundancy rather than being a stated goal becomes a necessary component of high availability networks, inherent in the design architecture. From RAID, redundant networking, to spare hot servers, high availability requires them all. From the use to the data and back again, almost every connection will be duplicated at least once, although in mission critical networks that require 100% uptime this may increase to 4, 6, or 8 duplications.

High availability networks are measured on the percentage of time they are online doing their assigned task, mission critical networks needing 24 hour uptime 365 days a year cannot fail, and uptimes are measured in the high 99th percentile. To put this in perspective, the architecture needs to be designed with goals of just one hour of downtime per year (99.99%), or just 5 minutes of downtime per year (99.999%)

High Availability Architecture Disaster Recovery Architecture

Levels of uptime in the high 99th percentile is only achieved thru developing architecture that allows part of the system to be brought down without affecting running processes and user access. Scheduled maintenance of primary servers can then be carried out over time periods stretching into several hours without loss of productivity.

The architecture of high availability networks is generally designed with two purposes in mind, local high availability, typically for networks in smaller corporations, and geographically distributed high availability networks that are more typically rolled out within very large corporations and where disaster recovery is an important design consideration.

A number of node configurations are possible in high availability architectures, and no single design can be described as best since each installation is always different requiring specific design features over others. The service level standards being applied will for the most part dictate the design chosen of the many that are commonly used, namely active/active, active/passive, N+1, N+M, N-to-1, and N-to-N.

To be effective, a high availability network needs to be configured to avoid conflicts in the event of a failed device. Planning the design architecture should promote reliability, availability, and serviceability (RAS) thru designated succession whether this is pre-configured or voted on by the remaining servers.

Correctly configured, most high availability servers include heartbeat daemons that actively send small packets to other servers in the network, which are in turn also sending heartbeat packets, and all are listening so that a failure is quickly identified and the failed server fenced off and it’s duties reassigned within the system. The avoidance of a split brain scenario where two or more servers attempt to control resources, a situation that will quickly bring down the network and could result in severe damage to data.

High Availability Solutions

High availability is no longer a luxury beyond the affordability of most corporations, in the 21st century it is now considered a requirement for almost all businesses regardless of industry and solutions are actively sought. Quite simply, a computer or server that fails might very well prevent the business from operating, and in today’s online world that may equate to significant lost revenue.

Within select industries such as government, financial services, legal, or health and hospitals, downtime is simply not acceptable. High availability of service is considered mandatory and may face regulatory oversight with penalties levied if uptime guarantees are not met. Meaning solutions that ensure minimal downtime and optimum service for the required number of users are actively sought out.

Solutions that encourage high availability comprise all facets of the IT network, and need to be designed with architecture that makes a failover anywhere in the system transparent to the user. This also offers the advantage that systems and components can be repaired or replaced without downtime or added pressure from users when IT perform maintenance.

High Availability Solutions High Availibility

Duplication of network components is easily the most popular solution for ensuring high availability across the network, typically most IT administrators install multiple RAID in their server farms or use storage area networks (SANs). Multiple redundant paths and failover routers and hubs are also used extensively and so too are backup servers that run hot and are ready to seamlessly take over resources if a failure is detected in the primary servers.

The need for duplication stems from most systems and components lacking fault tolerance that would allow continued operation despite a failure, forcing IT to create fault tolerant networks thru increased spending on backup components, and additional pipes. The cost of creating a dedicated backup network is usually beyond the budget of most corporations, with high overall costs of acquisition.

Third party data center and network leasing is a viable and affordable alternative, and leasing services within third party owned data centers that act as backup for critical network servers and components removes the onus on the IT department for planning and maintaining backup networks. By contracting out for backup services, complexity increases, but also allows for greater flexibility in testing failover procedures.

Designing systems and procedures that monitor performance of servers and network components and create log files, but more importantly generate resource usage reports over time are integral to high availability systems. Determining the correct solutions thru analysis of actual needs is preferable to running simulations of potential problems.

Training staff to recognize problems before they occur promotes a culture of excellence, helping personnel make better decisions and recognize potential problems before they occur, often be being able to read incomplete information. High availability solutions are complex, and trained personnel are better able to anticipate bottlenecks and failures, thus making less mistakes.

Adding redundancy at the staff level in these economic times will rarely be sanctioned, so reducing reliance on a single staff member thru cross training and task swapping supports high availability solutions. This needn’t be a threat to highly skilled staff, indeed their employability will increase.