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SAN goes virtual

Ian Jansen van Rensburg
By Ian Jansen van Rensburg, senior manager Systems Engineering at VMware Southern Africa.
Johannesburg, 18 Mar 2015

Today, more enterprise applications around the world run on virtual machines than on native hardware. Businesses have realised enormous benefits of cost, scalability and flexibility, thanks to virtualised CPU and memory resources. Networking is rapidly catching up due to the software-defined data centre (SDDC), which allows internal networks to be flexibly provisioned around the virtual machine layout rather than being tied to the hardware.

The next revolution will be in storage. Early virtualised environments suffered virtual server sprawl. Because it was so easy to provision virtual machines and their associated disk images, businesses often ran out of space because their storage was over-provisioned and under-used. Many enterprises that use storage area networks (SANs) to manage their storage requirements have fewer problems of this nature, but still battle with complexity of configuration and performance.

The world is changing towards a more agile and flexible method of managing and provisioning storage. In the current world, everything revolves around LUNs (logical unit numbers) on top of which virtual machines sit and within which applications run. The management processes are complex and take time to configure. And because different applications on the same VM have differing I/O requirements, storage devices need to have good random read and write performance, not to mention the potential impact on the network.

The new world

To achieve the full potential of the SDDC, a new software-defined storage approach is required to address storage-related operational complexity and cost challenges. In the new world, the SAN is still there, but now it's virtual. The hypervisor manages both the directly attached storage and the network connected storage, and serves it up as a highly-configurable SAN. Each node uses a minimum of one solid state and one spinning drive.

In the new world, the SAN is still there, but now it's virtual.

The SSD is used for both read caching and write buffering, while the spinning disk serves as the main storage. The SAN is enabled directly in the hypervisor kernel and can be switched on with two mouse clicks. This also means the policy management is at the virtual machine level where it should be for maximum control, rather than per LUN. And because the hypervisor sits in between the application and the hardware, all I/O goes through this layer. Because it is known from which VM or application it is coming, smart things can be done with it. Additionally, the hypervisor understands what the storage system has to offer and can communicate to the storage system what its needs are.

The virtual SAN fits neatly into the SDDC approach. The SDDC is about managing and provisioning resources in an agile way, allowing IT to meet the demands of business. For storage and the workloads sitting on top of it, it means resources can be abstracted and pooled, and then, through policy provisioning, its management can be automated. Besides the policy aspect, it is possible to automate the deployment of a new application through a common set of APIs.

The virtual SAN model is also immediately effective for a number of uses cases. Virtual desktops can be rolled out at lower cost with predictable performance. Test and development environments can provision needed storage quickly without having to acquire expensive external storage - just add a disk to a host or a host to a cluster and the hypervisor takes care of the rest. A virtual SAN can even be an inexpensive disaster recovery option in which a snapshot or backup can be redirected to any target within the cluster. Enterprises can now build up environments made up of dense building blocks with storage resources close to where they are needed.

Businesses have rightly complained that storage is as costly and difficult to manage as ever, even as servers and applications were rapidly virtualised. The virtual SAN model makes it a first-class citizen again: easy to provision and manage, with predictable performance, and as easy to scale as adding disks to a host or hosts to a cluster.

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