Rack space is an ongoing cost while the hardware is a fixed cost. Presumably they've decided it's worth having a slightly higher fixed cost per GB in exchange f

Rack space is an ongoing cost while the hardware is a fixed cost. Presumably they've decided it's worth having a slightly higher fixed cost per GB in exchange for a reduced ongoing cost per GB. (There's probably other benefits as well, such as reduced workload and just getting the space online now.) Let's take a look... They do have an oldish post on hosting costs: http://blog.backblaze.com/2011/07/20/petabytes-on-a-budget-v2-0revealing-more-secrets/ http://blog.backblaze.com/2011/07/20/petabytes-on-a-budget-v... A rack in 2011 cost them $2,100 per month (it's more now, guaranteed). Their racks look to hold about 11 machines. Each pod is then about $191/mo. Each rack thus needs 1.375 extra pods at "low density". That's $262.50 a month. Since you now need about 10% more pods, you're paying about $29 more in hosting costs per month per pod. Your savings are not $688, since you also need to construct 1/8 pod later. A low-density pod will cost about $2719, with is $340 split 8 ways. So real hardware savings is $348. Hosting costs eat that in exactly a year, and they are certainly expecting a longer life than that. (That's 2011 hosting costs, which are certainly lower.) So it's worthwhile to spend a little extra for the additional drives. (Of course, if they could get the extra five in with more modest hardware, as seems quite possible, that would be a sure win. But sometimes ease of development/assembly/spare parts wins over hardware cost.)