The storage appliance, not the guitar

David, from Western Australia, writes:

During my daily trawl across the more interesting places on the net, I encountered this little device, as I’m sure you have.

Naturally, I was interested... until I saw the bloody price. I could build my own happy little 1.5Tb RAID box for the cost of that thing and still have change left over.

But it did bring something to light. Its storage mechanism seems intriguing, for as much I like RAID, I hate sacrificing to the parity god, especially if I’m using 500Gb drives.

Which got me thinking. This Drobo thingummy seems to be an expansion of JBOD with some kind of parity calculator. Now granted, the implementation of this in a shiny box is reason you pay for this thing, however my question as it were is this:

Have you ever encountered a method of implementing this on a PC? I’ve done a bit of hunting and come up with squat, but I do remember you writing about JBOD related things on several occasions, so I turn to you as a font of knowledge, oh mighty Dan.

The Drobo box does indeed look like an interesting little thing, and certainly seems to be a step toward the home mega-storage Nirvana I've written about before. But it has its limitations, chief among which is exactly the same Parity God sacrifice you'd make with a do-it-yourself RAID rig.

If you only read the glossy main Web site, all you'll find is that the manufacturers allege that their storage scheme uses "advanced storage concepts such as virtualization, but it is not a derivative of RAID". Well, who knows what the heck it is, then, but it's clearly doing something analogous to parity RAID, otherwise it wouldn't be possible to yank a drive and upgrade it any time you liked. So, obviously, all of the data on any given disk must be reconstructable from the content of the other disks, and the amount of capacity offered up to the Parity God must be at least as much as the size of the biggest disk.

Drobo aren't really hiding this, though; their knowledge base confirms it. I suppose the thing could theoretically offer more capacity if it did real-time compression, but that'd make it hilariously slow and not gain much for the kinds of files that many Drobos are probably going to end up containing, anyway.

So if you add a 1000Gb drive to a Drobo that already has three 500Gb drives in it (ignoring real-gigabytes versus drive-manufacturer-gigabytes for now), you'll take your aggregate capacity from 1000Gb to 1500Gb. If you've got four 500Gb drives in your Drobo and swap one of them for a larger one, the actual capacity won't increase at all!

So I suppose it's basically working like RAID 4, but with support for dissimilar disks.

As with normal RAID, if you change the drive setup your Drobo may be churning away for hours. And, just like a rebuilding RAID array, a disk loss during this period will poleaxe the entire array. The Drobo does, however, have battery backup to prevent a mere mains interruption from clobbering your data. So you should factor the price of a UPS into your equivalent-PC calculations.

In answer to your actual question, no, I don't know of any remotely user-friendly way of doing this same sort of thing on a PC. FreeNAS could be a thing if you don't want to take the more traditional route of pirating a really expensive version of Windows, but plug-and-go it ain't.

Drobo really are quite straightforward about these capacity issues, though, including the powers-of-two versus powers-of-ten capacity rip-off. The knowledge base makes clear that four "500Gb" drives will only give you 1397 formatted gigabytes.

(It's also a neat hack that the thing reports 2Tb capacity no matter what drives you actually install in it.)

In answer to another of my immediate questions about the thing, it is also apparently possible to swap drives from a dead Drobo into a new one. But there is of course no way to read Drobo disks on anything else. Software RAID (and, in theory, quality hardware RAID controllers) gets around this vendor lock-in problem, but for home users it's not that big a deal, if of course you make backups. Which home users don't.

Oh, and as someone else has noticed, the Drobo site tagline currently says "whose" where it ought to say "who's". That's the kind of attention to detail you love to see from a storage vendor, isn't it?

8 Responses to “The storage appliance, not the guitar”

  1. Cods Says:

    This look kind of similar to the way that Windows Home Server seems to work. Well, as far as I can make out, anyway.

    Perhaps it's currently cool to say that RAID is so, like, yesterday?

    I've bothered Dan a couple of times over the past year or so, looking for the NAS/home server that sucks least, and he's been very patient with my dumb questions, but so far I've yet to see something that is reasonably priced and is also decently specified, although perhaps I just need to increase my definition of reasonably priced. I wonder if a WHS or a product like the Drobo might fit the bill? Up until now RAID5 has been at the top of my essential features list, and whilst I'm yet to be convinced otherwise, it's still interesting to see two products like these coming out, both eschewing the RAID approach.

    Meanwhile I'll wait for the price of the Thecus N5200 RouStor to come down a little. AU$1000-1200 is a lot of money when you still need to add drives!

    Yeah, I know, I could just convert one of the low-end boxen hanging around the house into an all-singing RAID6 server (next I'll be advised to run it under *nix), but as much as I like to tinker with PC stuff, relying on my tinkering for something like this doesn't leave me completely confident. Backups are great - but even better is having backups and never having a reason to use them.


  2. Cods Says:

    See! Would you trust me to build a server, when it seems I can't even use HTML properly? Ooh, that's ugly - sorry Dan.

    The links, for anyone interested are:
    - Windows Home Server Official Blog, Microsoft Technet -
    - Windows Home Server again, this time from Wikipedia -
    - StaticIce search for the Thecus N5200 RouStor -


  3. Daniel Rutter Says:

    Slightly broken links made more broken by heartless WordPress robo-fascism have now been repaired.
    -The Management

  4. corinoco Says:

    Speaking of NAS storage, I (stupidly) bought a Netgear SC101 without reading 'real' online reviews of it first. Magazine 'we won't bite the hand that feeds us' reviews all call it excellent. The actual forums rightly call this a piece of unadultered shite - then Netgear deletes your post. It's a nasty piece of crud that is now not even worth selling on Ebay. I am hoping, against all odds, that Netgear fix the bloody firmware / driver mess before PATA drives disappear. I'm not holding my breath though.

  5. Bedlam Says:

    Of course, relatively recent mobos have RAID 5 built in, and with 6+ SATA ports on some models, the parity sacrifice is minimal. I built such a box for my boss using paltry 320Gb drives for a real capacity of around 1.2Tb. And with the 90-odd gig a month of "Linux ISOs" he torrents a month, he sure as hell needs it.

    A word of warning for anyone trying a similar set up - Gigabyte has some hilariously undocumented bug that means WD HDDs *almost* work on their mobos, but not to the stage of having a continuously uncorrupted and formattable volume. Oh how we laughed for the 3 weeks of trying to get it working.

  6. rho Says:

    Might be worth looking at OpenFiler as well. It's a bit of a pain unless you have a Windows domain controller, or a LDAP authentication server already set up. But it's based on CentOS, which is a very stable distro; it has a Web-based management that's reasonably easy to use; and it uses LVM so you can make use of those random drives that computer enthusiasts tend to collect over time. Pretty much any computer made in the last decade will work.

    Overkill for the home user? Probably. But if shared storage problems vex you, this could be the sledgehammer you want to use.

  7. Cods Says:

    After reading this and taking the time to post a comment or two, I was all enthused - and ended up registering for the Windows Home Server beta. Turns out that I (along with 4.6 million others, I'm sure) got an invite to play with WHS, and I'm planning to throw together a bitzenbox and install WHS on it on the weekend. I might as well take a look and see if it looks any good.

  8. trentblase Says:

    When I first heard about this, I thought it might be using ZFS ( Maybe it does, but as the original writer mentioned, the price is absurd. ZFS is free, so anyone considering building their own NAS should check it out. It is utterly awesome.

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