Drive Economics

As of right now, I have a Drobo filled with 1TB drives that I’m pretty happy with. After a couple of weeks of pain the new Drobo has settled down, and we’re peacefully co-existing.

But I’m running out of space. With 4 1TB drives, you end up with about 2.7TB of usable space, and I’m at a little over 2 right now.

Now I could start throwing stuff away, but the whole point of a drobo is that you can just add bigger drives. So I decided to check things out and see what it would look like from a space/price point of view.

Now, you can’t just add one larger drive to the drobo, at least not one larger drive that’s bigger than all the others, because it won’t use all the space. If I toss in a 2TB drive into one of the slots, I won’t add 2TB of space, because it won’t have enough space on the other drives for parity data. It will just reserve that space. So at a minimum, you have to replace 2 drives.

That leave me in a situation where I have to install 3TB of drives to gain an additional .5TB of space, or and additional 4TB of drives to get an additional .9TB of space. Both because you’re discarding 2TB of space with the replacements.

So lets just replace all the 1TB drives with 1.5TB and 2.0TB drives.

4x1TB drives – current – 2.7TB usable space 4×1.5TB drives – $440 – 4.1TB usable space 4×2.0TB drives – $880 – 5.5TB usable space

so if I spend $440, I gain 1.4TB of space total. If I spent $880, I gain 2.8TB of space total.

In both situations I have 4 1TB discarded drives sitting on a shelf, or thrown in to replace scratch drives or whatever.

Neither of these options is very attractive. But there’s another way I can gain 2.7TB of protected storage for cheap: Buy another drobo!

4x1TB drives – $320 Drobo – $350

so for $670, I gain the same as switching to 2TB drives. But of course, I now have 8 drives in 2 cases with data across 2 volumes.

Of course another way to look at it is:

$880 gets you 5.5TB online, 2.7TB offline $660 gets you 5.4TB online, none offline

so for the $220 difference, can you find something to do with the additional 2.7TB protected or 3.7 unprotected?

And yes, I’m a little bored.

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