Lean machines: Data centre consolidation done right

We've written extensively on the whys and wherefores of moving some or all of your infrastructure into a data centre. But what about when you need to do the opposite and move out of a data centre? Sometimes this will be because you're downsizing, but often it'll be because you need to consolidate two or more data centres into one – as the result of a corporate acquisition, for instance.

The benefit of data centre consolidation is that your kit is already in one data centre or another, so you don't have to concern yourself with how to connect your own premises to the data centre as that's in hand already. So it's all about unification and then decommissioning.

Contract termination

The first thing to look at is the contract for your data centre. It's common for there to be a minimum term on the contract – even 24 and 36-month minimum terms aren't unusual, because the providers give price incentives for long-term contracts at sign-up time – so check when your minimum term expires and what the notice period is. Note that because data centre space is at a premium, you may be able to negotiate any early termination fees down if the provider of the data centre you're moving out of is desperate for space.

Space and power

Make sure you have space and sufficient spare power provision in the data centre into which you're consolidating your systems. Space is the easy one (just look at your rack diagrams) but be careful to calculate the power draw to ensure you're within the provider's limit. Of course, the likelihood is that you won't need quite as much power in the consolidated location as in the one being decommissioned (some of the LAN and security infrastructure will probably be duplicated between locations and hence can be trimmed).

Do I move my kit?

If some of the kit in the data centre you're closing down is getting long in the tooth, consider whether it's time to replace it. Moving equipment always has the risk of damage, no matter how careful you are. With new kit, you also have the option of ensuring it's got the latest version of everything at the latest patch levels and testing it before you move.

Can I virtualise?

If you run a virtual world, you have the opportunity to make your life incredibly easy. Even if the addressing structure of your various locations prohibits you from clustering the hypervisor hosts across sites, you can generally engineer a way to allow you easily to export the VMs from one to the other. The other bonus that virtualisation gives you is with addressing.

IP addressing

In rare situations you'll have Layer 2 connectivity between the data centres – an extended LAN rather than a routed MAN or WAN. Most of the time you won't have this luxury, though, and you'll have to deal with the problem of moving your IP address range from one data centre to the other. There are three common situations:

• If you have a virtualised world, it's a very simple job to replicate the IP structure from the site that's being decommissioned in the site in which you're consolidating. Just configure a new virtual network and bang it behind a virtual firewall
• If you have a physical world, you can do the same thing but you'll need to do it in hardware instead. So at the very least you'll need a router or a Layer 3 switch that can route between the subnets
• You can make the decision to change the IP addresses of the systems you're moving so they dovetail into the addressing scheme of their new home

Generally speaking, the third of these doesn't happen at move time: it simply introduces risk. I prefer to go with one of the first two options and then do the re-addressing later, system-by-system.