Box reduction: Picking the low-hanging green datacentre fruit

Virtualising the storage can drive up the array disk utilisation rates. With it applications think they have sole use of a logical unit (LUN) of storage but in fact it is mapped by the virtualisation software to any drive array volume that the storage admin people set up, and can be moved at will.

Thin provisioning the storage is an even better idea. Applications traditionally get allocated all the block storage they need over a period of time, such as 12 or more months. But they don't physically need all these disk blocks; they may write to just ten percent of them one month, another ten percent the next, and so on.

What thin provisioning does is to tell the application it has, say, a 100GB LUN, but actually only allocates 10GB. When it is close to getting filled up then another tranche of actual storage is allocated. Suppliers such as 3PAR, HP and Hitachi Data systems have this feature. EMC does not, yet.

It means you can defer purchasing possibly huge amounts of disk across your entire set of server applications and thus defer drawing down the electricity needed to power and cool it.

Another promising idea is de-duplication. Where you backup data to disk then de-duplication can identify repeated character strings in files and between files, and replace them with pointers. This can result in de-dupe ratios of 10, 30, even 30:1. You literally only store the information once. Where you would have needed 30TB of disk for your disk-based backups you can now make down with 5TB or less.

Suppliers such as Diligent, EMC's Avamar, Sepaton and others have this feature.

A further step you can take is to have secondary data, needed to be online but not accessed frequently, stored on a MAID drive array, with MAID standing for Massive Array of Idle Disks. Most of the disks are spun down and not consuming energy. If data that is on a an idle disk is needed then it is spun up.

Because most disks are not spinning, the drive array doesn't get so hot and more disks can be packed into the same space. Thus you save on power, cooling and space requirements.

MAID product suppliers include Copan, Nexsan and Fujitsu.

Lastly, you can keep on using tape or optical storage for tertiary data; data that must be kept but may not be accessed for weeks, if not months. Once data is written to the tape or optical media then that media can be taken off-line and left on a shelf or in a library slot. It consumes no power at all.

All in all, there are several incremental steps you an take to reduce the power and cooling needs of your storage and get rid of some drive arrays.

You may also choose to use newer, higher-capacity drives and thus reduce the physical number of drives you need. One 750GB serial ATA (SATA) disk can replace three 250GB SATA drives.

An ESG report, Power, Cooling, Space Efficient Storage, provides a very good description of various storage efficiencies such as these listed above and a few more such as relying on Snapshots to 'copy' data sets. It is a very worthwhile read.

Network kit

Box reduction in networking means replacing several boxes with few ports apiece with one box with many more ports; this is a port consolidation exercise. It is again a natural adjunct to server virtualisation. Instead of many discrete network links to individual server boxes you have fewer physical links to fewer physical server boxes which run many virtual servers all communicating over the same network links.

One's intuition says network link utilisation has rarely been as poor as server or storage utilisation. In fact, the actuality has been that communications links are choked by excess data rather than starved of data. The expectation is that network box reduction is not as practical or potentially reading as either server consolidation and virtualisation and the various storage box reduction tactics listed above.

Conclusions

The simplest and most practical step you can take to reduce datacentre IT kit power, cooling and space requirements is to virtualise your servers. The next thing is to look for incremental savings in your storage by consolidating separate islands into a single pool for the virtualised servers. Then look to technologies such as thin provisioning and data de-duplication to further shrink your storage estate. MAID and offline archive storage can further limit physical disk array sprawl albeit at the expense of slowed-down data access.

Storage needs in terms of the amount of data needing to be electronically kept are rising. Perhaps it is time to change the mindset of users and re-impose storage quotas to reduce the apparently remorseless flow of drive arrays into your datacentre. Otherwise, any greening you do undertake could bring you short-term wins only. In a few years time you could be back at square one.