John’s Blog

I’ve been meaning to pick up a Drobo for our house for quite some time — thanks to Aneel I finally got one last week — and, as I share below, I really, really like it. They’ve done a great job, and it should be a great storage and backup solution for us for a long time to come.

[quick disclosure: Greylock Partners, where I work, is an investor in Drobo.]

First off: Drobo is essentially a big box of hard disks that acts like a single disk. It uses a non-RAID technology called BeyondRAID to spread out data in a way that if 1 disk fails, you can still get to all your data. (There’s also a setting so that you can make it robust to 2 simultaneous drive failures, but that’s not the default, or what I’ve set mine on.)

It also has an extremely nice characteristic that you can always hot swap any drive for a replacement or a bigger drive if you run out of space. (Just another step towards robots being in control — when the Drobo needs more space, it blinks a yellow light at you, effectively saying, “Human, I require more disk — please run down to Fry’s and deposit the new disk beside my blinky light. That is all.” I, for one, welcome our new robot overlords.)

Anyway, back to the Drobo. I chose the Drobo S, which is a 5 bay unit that’s direct attached to a machine via eSATA, Firewire 800 or USB3. I dithered back and forth on whether to choose that one or the Drobo FS, which runs everything over Gigabit Ethernet as a networked file server. I chose the direct attached because we have an iMac that’s pretty much always on, and the vast majority of the data we want to store on the Drobo is from the iMac — and I figured this would be a simpler configuration. I’m still on the fence — I think I would have been just as happy with the FS.

The out of box experience with the Drobo is exceptionally good. The packaging is more like a consumer device, with easy-to-follow 1-2-3 steps on top, clearly marked, and the Drobo itself wrapped in a protective cloth. Essentially, here’s the process:

1. insert the disks into the Drobo (in my case, 5 1TB Quantums)
2. install the Drobo software onto the host computer
3. plug it in
4. run the Drobo dashboard to specify how you want the partitioning scheme to work, etc

Altogether, took about 10 minutes, and the Drobo was happily running, showing to my iMac as a 16 TB volume (even though I’ve got 5 TB of physical space and more like 3.7 TB of logical space once you factor in the redundancy).

That was really it — it couldn’t have been simpler. No complicated decisions, no significant forward looking capacity planning, no nothing. When the yellow blinky light comes on, I’ll feed it more disk.

To my mind, this is really the only solution there is that’s simple, performant, stable, expandable, redundant, and not incredibly industrial and expensive. It’s quiet (much quieter than I expected for 5 drives running) and doesn’t get hot, and so far has been pretty good about spinning down after disuse. (It could be more aggressive there, but might be pilot error on my part — need to look into it.)

Anyway, I like it a bunch.

Using it for backup with Time Machine

It’s worth talking about my use case here, since there is a minor wrinkle. The reason that I’m so excited & interested in home storage is that our family’s data needs are growing, quickly. We’ve got about 40k digital photos that are getting increasingly large per picture. We’re taking more and more HD video with our Canon 7D. Most everything we watch for SPL that isn’t streamed is ripped from other sources and stored. In fact, in the year or so since we got our iMac with what I thought was a pretty reasonably sized 2 TB disk, we’ve gone from about 600 GB of stuff to 1.3 TB.

It’s harder than you might think to regularly and reliably back up 1.3 TB in your house.

We had a 2 TB external drive that was doing it for a while, but that’s not really big enough once your main data set is over a terabyte, especially with Apple’s Time Machine, since it’s pretty aggressive about making deltas every hour, day, week, etc. So we needed something bigger than that, but the 3 TB drives aren’t too available yet, and I wasn’t really all that keen on replacing that one again in a year or so as our data grew.

Which is why the Drobo is perfect. Just add disks as I want backup to scale.

There is a small problem though, in the interaction between the design of the Drobo and the design of Time Machine. The Drobo just wants to be the biggest disk it can be — up to (at least) 16 TB, so it tells the iMac to just keep giving it data, letting it (and you, human with a car and a credit card) take care of the physical details.

Time Machine is designed to find an external disk (that you select), start putting files on it and then putting new (or changed) files on it again and again and again until it fills up the disk. So that’s a virtue if you’ve got a dedicated disk that’s backing your data up, to a point.

But since the Drobo advertises to the iMac that it’s a 16 TB disk, and Time Machine hasn’t really learned limits yet, Time Machine will happily fill up your physical space, which will cause your yellow Drobo light to come on, which will cause you to install a new disk (and repeat, and repeat), all the way up to the 16 TB that’s the maximum.

So that’s not great. What you really want to be able to do is to tell Time Machine to just use a certain amount of space and then start rewriting over older copies. There’s no way to do that at present in the Time Machine settings (which I feel is silly — with big disks like Drobo, it’s an easy thing to add), so you have to instead make Time Machine think it’s got a smaller disk than it does.

2 ways to do that: (1) partition the Drobo into a logical Time Machine volume, or (2) use sparse bundles. I didn’t want to do the first one, because in the future I might want to expand the Time Machine volume, which would mean repartitioning the Drobo, and losing my data in the process.

But sparse bundles (or, more precisely, sparse images), which I also use to encrypt my work and personal directories on my laptop, do the trick perfectly. With a sparse image, you can set up something that looks like a disk to your Mac, with an optional maximum size that you set, but that only takes up the space that it’s actually using.

So I set up a 3.5 TB sparse image that Time Machine backs up to — as it gets to full, it’ll do the right thing, keep the total backup space used under 3.5 TB, no problem. And I can resize the sparse image at any time in the future from the Terminal.

And that’s working perfectly at this point.

I used an Automator script called Time Tamer to do things pretty automatically for me. And there’s a good discussion of some of this stuff on a couple of blogs — this one was most helpful to me.

Bottom line: the Drobo S is going to be perfect for us, and I couldn’t be happier to have it. I know it’s decidedly nerdy to get excited about a storage solution, but there you have it. 🙂