Keeping the sprawl at bay

There's no such thing as an IT department with too much money. That's always been true, but budgets right now are universally tight. For many organisations I deal with, the question is not which 'nice-to-have' optimisation to leave off the list this year, but which essential project to delay.

This is not the only thing driving more and more organisations to virtualise their IT environments - there are many other factors like speed, reliability and flexibility - but making the best possible use of scarce resources is a big factor.

The savings of virtualisation come from the fact that the more virtual servers can be run on a single physical machine, the more energy will be saved and the less often new hardware will need to be bought. In most organisations, the business case for virtualisation is built on the assumption of a 'consolidation ratio' of between 10 and 20 to one; in other words, every physical machine will host 10-20 virtual machines (VMs).

Once virtualisation has happened, though, users quickly notice many other advantages. One of the big ones is the sheer convenience of creating new VMs. Instead of going through a months-long procurement process to buy a new server, a development or project team can commission as many new VMs as they need in minutes.

This is great - but if the housekeeping isn't done properly, the proliferation of VMs can slow the environment to a crawl and fatally undermine the business case for going the virtual route in the first place. It's such a common problem it even has a name: VM sprawl.

Part of the reason VM sprawl happens is the ancient human instinct not to throw anything useful away "just in case". So even though the project is wrapped up, all the files are archived and there are full backups of all the VMs which can be restored at a moment's notice - people still hesitate to delete the VMs themselves. Often the machine is unregistered so it's easy to forget about, but it's still there in a kind of un-dead zombie state.

Superficially, it seems less risky to let the old VMs hang around in case they are needed one day - after all, hardly anybody ever gets in trouble for not deleting something. But in reality, it is VM sprawl that poses the real risks.

The first risk is the one that really kills the business case: every zombie VM is still using up valuable system resources, especially expensive storage. Let's say it's been allocated 500Gb of data - even if that storage space is empty, it still can't be used because it's reserved for that VM. It's like putting a traffic cone in an empty parking space: it instantly turns free space into wasted space.

Combine zombie VMs with junk data like old ISO files and defunct system snapshots, and an entire storage array can be pushed to breaking point surprisingly quickly. The larger the company, the more people there are contributing to the sprawl, and the faster trouble will happen, no matter how well-resourced the company is.

Hardly anybody ever gets in trouble for not deleting something.

There's also a compliance risk: how many operating system licences does the company have? Every zombie VM is using up one of them. When the vendor comes to do an audit and finds the company over the limit, "Whoops, we seem to have overlooked that one" is not going to be a good enough excuse.

Business processes that prevent wanton creation of new VMs are one way to solve the problem - but a process that overcomplicates things also undermines the flexibility benefits of virtualisation in the first place.

Companies also need to implement thin provisioning, particularly for SAN storage space, which is notoriously expensive. Thin provisioning means the company can configure its VM with all the storage it thinks is required - but actual storage space will only be released when it is needed, up to the maximum the company has configured for. This enables the company to get the most efficient use of its entire available storage pool.

Another solution is to be rigorous about clearing out old and unused files - but to do that, they first need to be found. This is not a job that can be done manually - it needs specialised tools that can not only identify junk files, but also enable the company to delete them safely.

In the next Industry Insight of this series on how to make the most of the virtual environment, I will look at how specialised management tools can not only help companies to prune out the junk, but also help to monitor and right-size their environments to make the most efficient use of available resources.