SAN Storage

SAN (storage area network) storage is a type of computer data storage system designed specifically for use with large networks. It is very expensive but is very reliable, scalable and flexible. It is networ based in which the storage box is connected to the server through switches. SAN supports RAID technologies which provide variopus ways to optimize data. It provides ways for high data availability, faster access, protection from disk failures and faster recovery. These advantages come with high cost.

SANs are most commonly implemented using a technology called Fibre channel. RAID supports high-performance data communications technology that supports very fast data rates (over 2Gbps).

A SAN presents shared pools of storage devices to multiple servers. Each server can access the storage as if it were directly attached to that server. SANs make it possible to move data between various storage devices, share data between multiple servers, and backup and restore data rapidly and efficiently.

A simple illustration of How SAN and server interacts(www.vmware.com):

 

How they communicate?

Host sends embedded access request to SAN. HBA and Switches acts as the medium through which the request is send. 

The request reaches the Storage Processors which is the front interface of the SAN and communicates with the disk arrays eventually communicating with the LUNs.

Storage Devices(Disk arrays) uses RAID groups the disks and provides various functionality. The smallest unit of storage is LUN. 

When provisioning storage, the administrator uses management software to create LUNs. They can create, for example, more than one LUN from one physical drive, which would then appear as two or more discrete drives to the user. Or they may create a number of LUNs that span several separate disks that form a RAID array; but, again, these will appear as discrete drives to users. 

A given host might be able to access a LUN on a storage array through more than one path. Having more than one path from a host to a LUN is called multipathing.

LUNs can be shared between several servers. While implementing failovers, LUNs can be moved from one host to another. 

Zoning:

This is a way of providing access control within a SAN. In a physical SAN, LUNs may be shared across many hosts. By zoning, it is possible to logically group hosts and storage in a SAN. It provides a way of authorization. Only the authorized hosts can see the associated devices. Zoning lets you isolate a single server to a group of storage devices or a single storage device, or associate a grouping of multiple servers with one or more storage devices, as might be needed in a server cluster deployment.

LUN Masking:

This is used to make a LUN visible to some hosts and invisible to some other hosts. This is used to protect some LUNs from other servers which might harm them. 

Storage management itself is a very big area in an IT Infrastructure Management. But for a System Admin, Storage is an indispensable area and needs a really good understanding of the way storage works with servers. Hope the above descriptions of SAN would have helped a little.