Technical Education

Storage Area Network (SAN)

Storage Area Network (SAN) is a high performance oriented dedicated and consolidated data storage network, whose principal function is to communicate with computer servers and to facilitate data access to them. The SAN can be located offsite and may comprise of disk arrays, robotic libraries, tape libraries and optical jukeboxes. But it appears as local data storage to the operating system on the servers, which access it. As there is a growing number of network topologies, which are having physical and architectural properties, SAN doesn’t need to depend on Fibre Channel or Ethernet or any other specific interconnect technology.

Storage Sharing

Storage Area Network offers universal connectivity of storage devices and computers as it depends on the client/server model of communication. Let us take a paradigm, to understand the situation completely. By deploying a number of multiple servers, an organization creates a number of unconnected islands of information. Each server island is accessible by one computer, but cannot be accessed by others.

Under these circumstances, if computer B needs to communicate with the data of computer A, it needs a copy of the data from the server A. In this situation, the moving of data between two computers depends on three popular techniques which are file transfer, interprocess communication and backup, which is a criterion. Let us assume that the data transfer from computer A to B is established. But the computer B will face a situation, in which it has to work with the data that is out of date simply because the copied data was not in a timely fashion. The copying of data may also cause costly errors, due to the extra operational complexity, taking place in between the two servers.

At this point of time, a SAN architecture concept will be offering a perfect solution for this entire situation. In a Storage area framework, all the servers are physically connected to all storage devices. If server B needs some data from server A, instead of requesting for a copy of data from server A, it can access the data directly from the devices, on which server A has stored the data. This is possible, when the data storage acts as a common access point to all servers, instead of a single server. Hence, as SAN operates on universal storage connectivity, it has power implications on Information technology.

SANs universal connectivity eliminates the need of scheduling data transfers in between the servers. It also eliminates the need for purchase and maintain of temporary storage, meant only for a data transfer to take place to another server. If two servers are running different applications, one need not worry about the sync of the data copies as they are working on the same content.

Since SAN storage only offers block level operations, it doesn’t provide file abstraction. But if the file systems are structured on top of a storage area network, then it can also provide file access and is known as SAN file system or shared disk file system.

In large enterprises, storage area network is seen as a storage pool for the servers, which are connected via a network. It simplifies administration, as it is better than managing each storage media, for each server. This will also make the maintenance of the storage easy and the scheduled backups will also be simple and can be managed in an easy way. In order to support data continuity, SANs are often deployed in remote locations and are maintained in conditions, which can offer instant disaster recovery.

SAN Infrastructure

Storage area network often relies on Fibre channel topology, which is specifically designed to handle storage communications. As Fibre channel provides faster and more reliable access, it is used as basic protocol in SAN infrastructure. A Fibre channel also known as Fabric relies on the concept of local area network. However, they are certain distance related limitations for Fibre channel topology and so it connects to off-site locations via the Ethernet powered iSCSI structure.

But from the past few years, due to the highly expensive Fabric Infrastructure, most of the SAN architecture is being laid on iSCSI protocol. This has not only brought the cost in establishing a SAN infrastructure, but also will be flexible to work with as it is ubiquitous.

Self-Healing Benefits Offered by SAN Storage

Self healing SAN storage is a data storage, where restoration of storage and data is done from a failure, before RAID rebuilds the data of a failed disk. Moreover, end to end error detection and repair is offered without the need of replacing hard drives throughout the systems warranty period.

It is a known fact that hard disk drives are the storage media, which are usually used in SAN. By having a self healing storage network, elimination of potential cause of drive failures can be observed. To reduce drive failures, heat reduction and vibration reduction need to be observed, which improves drive’s reliability. Vibration can cause drive failures and also can instigate skipping of writes and reads, of adjacent drives. No matter, how efficiently the drive manufactures design the drives, still the vibration can cause failures, which can result in downtime. However, this problem can be overtaken, by building individual drive housing, so that there is uniform rigidity throughout the system. This can be done by installing drive shelves front to back, alternating throughout the array shelf. This is known as counter mounting.

Coming to minimizing the heat, this can be done by increasing the airflow in the drive enclosure. By placing the drives in a side by side position in front of the drive bay, tight packing of the components can be avoided. This will not only improve airflow and decrease heat upsurge, but also will reduce vibration.

If a storage system takes measures to resolve erroneous disk drive failures, this saves a lot of money, time and also eliminates the risk of facing downtime. By changing the physical design of the hardware, reduction in drive failures can be observed. When the drive shows initial signs of failure, one can reset or power cycle the drive in an automatic way, which doesn’t show any impact on the regular system operations. When the drive seems to be well enough to be restored, then it can be restored to normal operations. If still the drive power cycles are unable to correct the problem, then self healing system will be having the ability to perform a full remanufacturing process.

In most of the cases, almost 70% of the drives deployed in SAN architecture can be repaired. So, as a result, one can save money, reduce data vulnerability and can make sure that mission critical operations can achieve high performance levels.

Pros and Cons of a Storage Area Network SAN Storage

First, let us go for the benefits of the SAN storage and the later on trace out the disadvantages of SAN storage.

Storage Area Network Benefits

  • Disk utilization is utmost – in a SAN architecture the disk utilization is utmost, as all the storage media are offered as a centralized storage and can be managed as a single entity. This makes the IT admin to assign the storage in a more intellectual way for the servers. In the absence of SAN, buying tons of disks and sticking to assigning of data will be an expensive.
  • Mission critical solutions get Dr assistance – When multiple servers dealing with mission critical applications are deployed in the data center, then recovery of data becomes tedious, in the event of catastrophes. But in SAN environment, data continuity is available as a quick solution. This helps in reducing the downtime for mission critical applications, to be accessed by users.
  • Availability and scalability – every enterprise expects availability and scalability from their data centers. SAN architecture is designed in such a way that, it offers mission critical applications enriched by availability and scalability. It is sophisticated enough, to alert the IT administrator, about its ill health, if in case, one of its parts are going bad soon. Moreover, the algorithms used in SAN are consistent enough to protect the data from all kinds of risks leading to downtime. Moreover, its scalability option can be flexible enough according to the data growth of the organization.
  • SAN offers quick backup – a quality backup of data, can save an enterprise during disasters. But if the backup is taking a lot of time, usually, most of the IT managers schedule it once in a week or neglect its existence, as it is too time consuming. But this can incur losses for an enterprise if situations deteriorate. But SAN offers speedy backup and so it will be a major benefit for an organization.

Storage Area Network Benefits

When right expertise, budget and business requirements are allotted to the data storage, then SAN architecture will be much beneficial. If in case, SAN storage requirements fall into the below mentioned scenarios, then going for a SAN storage doesn’t make sense.

  • When an enterprise has only few servers which are inexpensive – Enterprises which have hundreds of servers will find SAN storage much beneficial, as it offers centralized storage and management. But those organizations, which only have few servers, will find SAN storage expensive. It is a known fact that, SAN offers the same features, irrespective of the size of the organization or number of servers. But justifying its cost against its existence is also needed as the equipment to establish a SAN framework is too pricey.
  • When disaster recovery is essential for only a single application – disaster recovery is essential for an organization and so SAN offers complete protection to the data accessed by application through its RAID influenced hardware. But having SAN installed for single application will be unwise, as the data recovery, during a disaster can also be done by a software. Software based solutions run on the servers, where data needs to be mirrored to a primary location. When this can be done by software, then utilizing SAN is almost expensive for single application.

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