Really, SAN is better is it? Add another 40 Watts per fibre channel port, another few kilowatts per cabinet of jumped up Linux boxes that you spent £10k each for because it was called a 'data mover'.

And as for MAID, most of the power cost in a current corporate data centre is the fixed overheads of the building, controlled by the power provisioned to the kit, so even ignoring the issues of heavily virtualised storage keeping those 'idle' disks spun up, the massive power supply ratings of MAID systems mean they will chew through the power, spun up or not. If you want some greener storage consider internal SAS disks that actually shut down when a server is idle or maybe a nice big optical or tape storage array at a fraction of the power requirement.

Next time you are looking for storage and the vendor's green paint is still not dry, before buying the claims about reduced numbers of disks in their expensive box remember the cost / performance / energy argument is two sided for SANs and count up the energy and financial costs of all the 'junk that isn't disk' as well.

So, you virtualise your servers onto less hardware boxes, hasn't this just changed the ratio of 'hardware boxes performing server functions' to 'hardware boxes performing storage functions'. Do the storage boxes use significantly more power than they did before we all virualised our servers?

I'm not sure what my point is.

Virtualisation and centralised storage can both help to reduce power in different ways.

With virtualisation, you can reduce your processor count by making one piece of hardware work harder. The processor will of course use a few more watts, but overall by eliminating one or more machines you reduce the energy use.

With a SAN/NAS, you avoid having to purchase many servers with more storage than is initially required, or with the possibility to upgrade in the future (and hence beefier power supplies). Instead you concentrate all your storage and can reduce your drive count overall. Avoid having lots of little RAID arrays, and instead have one or more larger SANs or NAS. It's also much easier to manage capacity since upgrading the storage on a server (real or virtual) can be done in software.

Who cares if storage arrays start using proportionally more power when the number of servers and overall power consumption is going down?

Of course the downside of both approaches is that if something breaks, a good proportion of your services disappear suddenly :-)

Oi!

Wasn't the headline on this one about 'Chelsea Tractors' [UK] rather than 'Hummers' [potty mouthed gangsters and gubbernators] once upon a time? If you are going to pander that hard wouldn't a black and white costume and a handful of bamboo be in order?

Our memories last a little longer than you think Mr Ministry of Information! All go fetch my coat shall I? Cloakroom 101?

Actually, every server consolidation exercise I've been involved in has seen the removal of many DAS units (usually SCSI) and their replacement with SAN arrays. Each of those DAS units, whilst also being underutilised storage, also had small, inefficient PSUs whereas the SAN arrays used larger and more efficient PSUs. In one datacenter I did the figures and I saw a drop in power costs where I could show the arrays were saving us 30% on power over the DAS units they replaced (plus also giving savings in admin, more efficiently utilised and therefore cheaper storage, easier replication, backups and DR, and savings in support costs). And that case was before thin provisioning which we now can use to allocate a large disk space in an array but start with only a small amount of the disk actually there, and then actually only add the disk as we get near the point where we need it (so less unused disks idly spinning away and chewing up current). In the survey mentioned, did they ask the same users that said they allocated more storage per server if their storage was better utilised and therefore likely to be less power-hungry after they went to consolidated virtualised servers?