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Storage Area Networks (SAN)

The management of storage has become a key issue for IT systems in the last few years. As the amount of storage increases and the demands for high availability of storage becomes more prevalent, having disparate pools of storage across many servers becomes ever more complex to manage.

In the last few years, we have seen an increase in the availability of the Storage Area Network (SAN). In simple terms, this takes all the local disk storage usually found in servers and consolidates it into a single, large pool. However, these devices are more than just a simple NAS box. They concentrate on making that storage highly available as well as providing the tools to carve it up into appropriate capacities.

One of the biggest management headaches with traditional server storage is we typically find large pools of unused storage, while pools on other servers are bursting to the seams. A lot of support time can be spent relocating data and then having to change application configurations (which point to that storage), user short-cuts, shares and drive mappings as well as backup configurations.

The SAN allows these key servers to be provisioned with only a small amount of local storage to hold the operating system. Using a high performance network data access protocol (iSCSI), the required storage is then carved out on the SAN and accessed across the network by the server.

The SAN devices can be made redundant and a well designed solution will be able to suffer the outage of a SAN server with no downtime or performance impact to the network.

Virtualisation

SAN is also a key component in designing a redundant VM network. The Virtual Machine hard drives are placed on the SAN storage. The Virtual Hosts then run the virtual machines from the SAN. Systems like VMware VMotion then allow these virtual machines to be moved from one host to another in real-time while they are operating.

After a significant amount of market research, Exmos selected Lefthand Networks (now part of HP) as their partner for SAN. Left Hand Networks were the first SAN OEM to provide high performance iSCSI on their devices (having been built for iSCSI from the ground up).

As well as providing traditional SAN server appliances, HP Lefthand also makes their SAN solution available as a virtual machine (VM). While initially this may seem a somewhat strange idea, it is the ideal starter solution for building a fully redundant VM network running on as few as two traditional servers (whereas with appliances it would require two SAN appliances and two servers). This brings the benefits of SAN/VM easily into the mid range of the SME market place and giving these organisations network redundancy capabilities that just a few years ago were purely in the realm of the enterprise organisation.