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Lean machines: Data centre consolidation done right
Dump the junk and shape up, soldier
You've already got connectivity to the data centre into which you're consolidating, but you need to have a quick look at a couple of aspects. First, confirm that you have enough bandwidth between the users and the data centre – if you're putting more apps in one place, you'll be hiking the load on the links. Second, verify the redundancy that you'll have in your network links, as you'll be decommissioning some of your connections and that might have implications on diversity of connections. When I've closed data centres or offices in the past, I've sometimes swung a WAN circuit or internet link from the closing site to the consolidated site in order to preserve diversity.
Continuing this logic, make sure that you consider the routing changes you'll need in the network. If, as is likely, you'll be moving an IP range from one site to another, you'll need to consider the routing across your network. My personal preference in a WAN is to use static routes between sites (they don't change much, and I've seen people break their worlds by using dynamic routing and firing up a device that starts throwing routing updates around) and so it's a simple case of updating the various routers on the network at move time.
Clean up your firewalls and any other devices that know about the location that's being decommissioned. I've often been infuriated when I've inherited a network and have been puzzling over what some of the rules mean, only to be told: “Oh, they're for the old office in <wherever>, we closed that years ago.” Your auditors will like you if you clean up the old rules too.
Disposal of the kit
You're highly likely to be disposing of equipment, so consider how you're going to do it. If you're dumping equipment then arrange for the disks to be securely destroyed, but if some equipment has a resale value then take advantage of this to get a bit of a budgetary boost. Even if the kit is very old you'd be surprised that people want it: I had two potential buyers for a seven-year-old phone system I was binning, for example, because it was out of production and they both wanted it for spares.
Backups and archives
Many of us have age-old backups of our systems that we keep either for legal/tax reasons or because the data retains potential value, and we live with problems such as having to hang onto legacy tape drives in order to read obsolete tape formats. If you've decommissioned a site and evolved the configuration (IP addresses and the like) to fit the new location this precludes you from easily restoring from a backup when something goes wrong. So be mindful of how you might, say, achieve a bare-metal restore from a tape that contains an image of a server that no longer exists with IP addresses that are no longer valid.
Asset register and diagrams
Finally, record the fact that you've consolidated your data centres. Archive the old network diagrams, store the documents that show the mapping of old servers to new, and where you've relocated equipment ensure you update the diagrams and the asset register appropriately. Knowing where stuff is is essential, and because you seldom actually relocate or decommission something in a data centre it's easy to forget to log the change when the time comes.
I've generally found the consolidation exercise very straightforward, for both data centres and offices. It's always a whole lot easier reducing the amount of kit and closing sites than adding kit and locations, and the complexity level of consolidation is significantly lower than that with expansion. The focus actually moves to the task of planning and executing the logistical side of the exercise; plan carefully and make sure you run all the way through to the disposal phase and you'll also find it straightforward. ®