By now most organisations have enjoyed the benefits of server virtualisation and can relate how it allowed server consolidation, reduced power consumption, averted future server purchases and increased agility by reducing the time required to deploy a server.
Storage virtualisation’s benefits are a little harder to understand, but it is still worth making the effort to adopt the technology for several reasons:
1. Storage virtualisation reduces complexity
Over the years, many organisations find they acquire different storage arrays from different vendors. Most are acquired because it makes sense to do so at the time of purchase, but the result is complexity as several management tools must be deployed – each dedicated to a single array or to arrays from one vendor.
Operating multiple management tools is unsustainably expensive and complex.
By virtualising physical arrays into logical pools of storage, two benefits accrue. One is easier management, as virtualising arrays also means using a single tool to manage them all. The second is that users find that when they treat all their storage appliances as a logical pool of storage, capacity that was hidden on one machine is easier to find and use. The result is that space can be used, deferring or averting the need for extra storage purchases. An additional benefit is that virtualising storage allows users to store data across devices from different vendors, an arrangement that is very hard to achieve without virtualisation.
2. Storage virtualisation makes it easier to allocate storage
One of a storage administrator’s least favourite chores is ‘provisioning’, the job of configuring a storage array so that its capacity is portioned off for different purposes.
Provisioning is unpleasant because it is tedious, and also because it sometimes results in storage capacity being walled off from use. This is a wasteful practice that makes storage appliances less flexible to operate, but is sometimes necessary for technical or business reasons.
Virtualised storage removes many of the factors that can see provisioning become wasteful.
Again, the reason is that considering multiple devices as a single logical pool of storage brings
more flexibility than only allowing users to see storage capacity in a single device. Once you look
at storage logically and provision from a pool, the constraints of individual devices go away and
so do many potentially wasteful practices.
3. Better disaster recovery
Imagine your storage area network (SAN) were to be destroyed.
Fortunately, you have backup tapes of all your data. But in many cases you would need the same equipment in order to put that data back to work.
Because storage virtualisation is less reliant on tight coupling between your data and the hardware it runs on, virtualised storage will often mean faster recovery from disasters. Virtualised storage can also mean you don’t need to maintain replicas of infrastructure at a disaster recovery site, thanks to its ability to allow access to data without a replica of the original hardware.
4. Better tiered storage
Tiering is the practice of matching data to media, so that important data resides on fast media.
This is a worthwhile exercise because some data is accessed a lot, and some is hardly ever required. Web applications such as online booking systems illustrate this situation: the data pertaining to a concert that goes on sale online at 9:00 AM deserves to reside on high-speed media. Last year’s accounting data does not need high-speed media.
Most storage arrays now permit tiering, as they can use different types of storage media. Virtualisation takes things a step further by allowing you to identify media across all of your storage assets, and create a virtual tier.
For example, imagine you have three storage arrays, each of which includes some very fast solid state disk. Virtualised storage allows you to combine all of that fast storage into a pool. The result is that when you need to place a lot of data in a fast tier – such as when a concert goes on sale – you can do so by accessing resources around your organisation instead of relying on one storage array.
5. Virtual storage improves server virtualisation
Virtualisation vendors have tuned their software so that when you virtualise servers, especially large numbers of servers, they are ‘happier’ residing on virtualised storage.
Even if this were not the case, virtualised storage arrays would be a sensible place to store virtual servers. This is because direct-attached storage (DAS) is already a bottleneck for many servers. When a single physical server hosts several virtual servers, input/output demands on its DAS disk increase. A storage area network’s higher throughput means servers will gain faster access to all sorts of data.
6. Virtual storage lets you take advantage of advanced virtualisation features
Virtualisation vendors like VMware have developed useful new tools like VMotion that allow you to move servers and data between physical locations. This is a useful disaster recovery and business continuity tool, and also enables new models such as ‘follow the moon’ computing that sees workloads shifted to facilities at which power is cheapest (which is often the case at night).
It is difficult to use these tools – and therefore to access the benefits – without virtualised storage.
This was first published in July 2011