In the end, though, power companies may be frothing at the mouths for these new disk-based backups. Though they are efficient and physically easier to manage, they are the gateway to an entire floor of hot, hungry, and heavy disk.
For example, choosing enterprise library and VTL systems at random, a VTL 'A' disk array taking up 6.7ft2 of floor space is boasted to provide up to 60PB of storage experiencing maximum deduplication with compression (50:1). The power / cooling requirements, and weight for this maximum build are respectively 7.1kW / 22,300 BTU/hr, and 240kg.
On the other hand, Tape Library 'B' at maximum configuration takes up 202.8ft2 of floor space, and provides 11.1PB of LTO-4 tape in a single enclosure. The power / cooling and weight for this dual-row library are 8.78kW / 30,000 BTU/hr, and about 7100 kg. At a glance this looks fantastic. The big question is what do you do with all that leftover room?
Everyone is always clamouring for more storage. Where do you put it? Well, with the floor savings above you can fill it with two Disk Enclosures 'C' with maximum configurations, for example. Together they advertise about 30.8PB of raw tier 1 storage taking up a total of 153ft2 in the person of 18 racks. Each of these racks individually requires, on average, about 6.15kW and 20,000BTU/hr. In total you've also added nearly 20,000kG to your floor.
Granted most environments would not require the drastic technologies described above, and the tape library vendor for B was friendly enough to point out that they offer more cost and environmentally efficient solutions. For argument's sake though, these numbers show that replacing tape with disk is a staggering improvement on a 1-to-1 basis, but only if the space saved stays empty. If, however, that space is used as a home for new disk enclosures the Earth will cry out for more of Al Gore.
Disk is heavy, runs hot, drinks a lot of juice, but you can deploy a lot more of it. Instead of a single library B consisting of mostly empty space, in its place you get electricity and cooling bills for 19 or so racks of disk draining your budget and piling on the carbon emissions.
[Note: these numbers were derived from online data sheets provided on several vendor websites, and have been rounded providing for a level of mathematical error and misinterpretation.] About the author: Brian Sakovitch is a senior consultant at Glasshouse Technologies (UK), a global provider of IT infrastructure services. Brian has followed a 6 year path in backup technologies ranging from hands-on installation and implementation, to design and theory. Three of those years have been with GlassHouse US focusing on a number of predominantly backup related engagements for companies of all shapes and sizes.