High availability- explanation

High availability is a term used to describe a system or a service which is ready to be used, therefore “available”, almost all the time. Availability refers to the situation when a user has access to and can use the resources of a system, service or a device, either to work, add new elements or use the databases. If user cannot do any of those, it is said they are unavailable.

The time when system is not available is also called downtime. High availability ensures that the required level of operational performance is met. There is a scale of availability listing the percentage of overall times when the system is unavailable. In the case of high availability this “almost” is a matter of about 5 minutes a year when the system is unavailable. This is 99,999 percentage (five nines) of availability. There are two types of the periods when a system is unavailable. One is scheduled and the other unscheduled downtime. The first occurs when e.g. a new software is installed and a configuration changes or system reboots are necessary. During these, the system is also unavailable, but they are planned actions, that is why they are called scheduled downtime. The unscheduled downtime is caused by accidents, such as software and hardware failures or blackouts. The damages and losses caused by those unscheduled downtimes can multiply when unavailability increases. Whereas, the scheduled downtime for some systems will not impact the functioning of the whole systems, for example when in an office they occur at night, because the people working there are at home and do not use the system. Also, there is a relation between complexity of a system and its availability. The systems that consist of fewer components tend to have higher availability than the more complex ones. This is because there are more elements that are threatened by potential failures.

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Nas device, os, storage.

Network attached storage is a storage solution which provides centralized storage and file sharing over a computer network, together with software for storage management and security. Network-attached storage refers to single hard disk-based devices that connect to a network over Ethernet or TCP/IP, and use file-sharing protocols that allow computers to access their disks as remote volumes. A storage area network is used more in enterprise-level businesses, and consists of a network of Fibre Channel-connected storage devices (usually multiple disk arrays) that communicate with servers as large-scale local disks. NAS OS can be a separate product or available with NAS device. IT providers have started to build their own storage operating systems onto the boxes, sometimes hardwired in ASICs, but more often than not as software running in a kernel operating system or a fully-fledged server OS. Storage software approaches are increasingly preferred because of the ready availability of universal operating system platforms, whether from commercial OS producers such as Microsoft with its Storage Server or from the open source community Linux or BeOS. Therefore, a NAS device is a lot more than simply a box of disk drives. In fact, all storage systems, from the most basic USB-attached or SCSI direct attached storage (DAS) array to the most exclusive storage area network with iSCSI or FC target, most products proffer at least some additional features in their storage servers. This is also the case with NAS OS. Many NAS OSs offer additional benefits. It is possible to store music, movies, and photos on a centralized server and stream content to multiple computers, since there are storage devices with NAS OS which feature media server functionality. NAS OS can provide advanced backup capability through software, a USB port to connect an external hard drive, or RAID support to back up files. For users who want to access the storage drive remotely, there are NAS OS products that offer access over the Internet or FTP.

Effectively managing storage

Storage software is an indispensable part of data storage system. The best storage software centralizes and controls the storage resources, helps reduce the complexity and costs of data storage, provides its efficient management, improves data availability, management of storage devices, monitors and tracks the performance of network storage systems e.g. in Storage Area Network or Network Attached Storage.

One of indisputable advantages of storage software products is that the installation and configuration of most applications takes usually only few minutes. Sometimes, the storage software is pre-configured for immediate use. It consists of several applications, including performance monitoring, file systems, volume management, virtualization software, file, audio, mail and surveillance managers. Its characteristic feature is that it odes not serve for storage of system files but data. The most popular mass storage devices will include tape libraries, RAID systems, hard disk drives, magnetic tape drives, optical disc and magneto-optical disc drives and older floppy disk drives. Storage devices differ from memory devices in that they retain data permanently, even when the computer system is turned off, whereas memory drives such as RAM (random access memory) does not save the data in this case. They can be used in most efficient way only with the dedicated storage software. The applications used for storage management enable a company or a private person to manage their storage system. They usually cover storage resource management (SRM) and network storage management software, performance monitoring, file systems, volume management, virtualization software and security software. Many IT companies for example open-e offer a universal tool for effective storage management. You can also find many trial versions and open source applications. They also include tools which are used for virtualisations and cloud storage. A storage software allow data to elastically grow, shrink or migrate across physical machines in a cluster without downtime, server failures or interruptions.

What is Fiber Channel

Fibre channel is a standard of network technology for data transmissions between computer devices. At first it was used for storage networking - connecting computer servers to shared storage devices and for connecting storage controllers and drives between each other. They can be made of optical fiber cables as well as of copper wires which are twisted. If optical fiber is used a medium, the channel can be very flexible - devices can be as far as ten kilometers apart. For shorter distances the copper cables are used more often. Fibre channel was the first technology to be adopted in storage area networks. Storage area network (SAN) is a network of storage devices that are accessible to servers and allows for resource consolidation and simplifies administration. Fibre channels are faster than SCSI, another type of network technology. They reach gigabyte-speed which is why they have become more common than SCSI in the case of SAN. The SCSI commands can also be transported via fibre channel protocol. Storage area network has been mainly deployed in enterprise storage, which, when compared to the consumer storage, needs higher scalability, higher reliability, better fault tolerance, and requires much more investment.

The large scale of this type of storage involves disaster recovery and advanced backup solutions, which are parts of a large-scale business continuity plan. Fibre channel offers three types of port connections. In limited-connectivity “point to point” topology two devices are connected to each other. “Arbitrated loop” has a set of devices connected to one another in a ring – when one device fails, the whole system is interrupted. The most reliable typology is the “switched fabric”, where all devices are connected to switches which convey the traffic and connection between ports. Here, in the case of one port failure, the functioning of the rest of devices is not affected.