In simpler language, when you RAID together dissimilarly-sized drives, you let the overage of the larger drives go unused. The Drobo merely then RAIDs together that unused space (potentially recursing several times) and adds it to the space provided by the first RAID set.

Cleanly said.

With the substitution of larger drives for smaller, does the Drobo ever grow the first raid that was created?

Good question. I have no idea. Probably.

I suppose it could reconfigure the second raid vol to be like the first, then somehow consolidate them into one.

Holy crap, Data Robotics has just released a DroboPro Elite. It's basically the 8-bay Pro but with two ethernet ports for iSCSI and without Firewire or USB drive access. Without drives, US$3500.

WTF!

Also a new Drobo S 5-bay model, without drives @ US$799. Yeah, that's 2x the price of the 4 bay model. It leverages the 8-bay's ability to have two drives fail safe.

Their NAS adapter doesn't work with the new models and they warn that accessing such volumes over a network would be very slow. Guess they've never seen a NAS from other companies with decent processors pushing over 100Mbytes/sec - which their direct-attached devices can't even manage.

I'm already waiting for payment instructions from a vendor for a ReadyNAS Pro which I hope to order within the next day or two. Still wish it had more than 6 bays, but there's not much I can do about that.

My ReadyNAS Pro is currently initializing the 4 1.5TB Seagate disks I dumped into it.

Here are some thoughts on the product...

Build quality: Sub-par for something costing this much. It's basically a small form factor PC case with drive rails. The drive brackets/caddies are flimsy and prone to insertion or removal problems. The slide action/fit of each rail/caddy is different, with a couple on the bottom being quite difficult to slide in and out. They include exactly the amount of screws you will need for 6 drives. Seeing as these are not the same length or head you'd find on typical drive screws, they should have included extras.

The instructions and quick-start guide are the worst I remember seeing for any product from any American company. Terrible.

The Mac OS software looks like crap. They didn't even take the time to make a proper icon. Not of huge importance, but it makes a very bad first impression when laying down over a grand for an empty box. It's shameful.

The web UI is very mid-90's design, though it seems to work. Many items are worded poorly or made overly complicated. Settings possibilities look decent enough though.

The big drawbacks of this product over a Drobo Pro are that it holds two less disks (6 versus 8) and that it can only protect for up to 2 disk failures while the Drobo protects up to 2 SIMULTANEOUS disk failures. Let me explain the difference... In the ReadyNAS, you can have up to two disks fail at any time if so configured. But you must replace those disks in order to gain back any protection at all. In other words, those disks fail but no rebuild is performed until you put in new disks. With the Drobo, the system will start rebuilding each time a disk fails. That means once the rebuild is complete you can have another two disks fail, provided you have enough free space of course. The unit not only dynamically expands, but it can dynamically contract if you have little enough data to do so.

Of course on the flip side, chances are your Drobo Pro will crap out and bork your entire array during the rebuild. But the idea and theory are nice. And of course the ReadyNAS isn't pig-slow like the Drobo and can support multiple simultaneous users effortlessly.

If you monitor your array you shouldn't just let it sit there after a disk failure, so in the real world, the dynamic down-sizing isn't likely to be an issue. But having two more drives bays would be nice. So would not having to use caddys.

How are you protected against two simultaneous drive failures. RAID 6 can't/doesn't do that (was thinking RAID 5 + hot spare). If it has to rebuild when one disk fails, what happens when the second fails while rebuilding?

Is that using RAID 6 then?

I'm assuming you're saying that it starts to decrease the file system size as well.

The ReadyNAS should offer RAID 6 as an option, and that does allow for two simultaneous drive failures. Any two drives could fail at any time and data would still remain. The difference though is the ReadyNAS won't downgrade the RAID level to 5 or 10, shrinking the array. It will keep data in a RAID 6 stripe, and will expect at least one drive to be replaced to get back to a level of redundancy. A Drobo Pro left alone with 2 drives dead would eventually return to redundancy, as long as there is free space.

The Drobo units really like to mix and match RAID levels, and migrate between them. This works ok in higher end enterprise SANs to still keep performance, but in a small box like the Drobo, it's mostly helpful to facilitate the ability to mix various sized drives, at the cost of performance.

Holy shit. I've just spent a few hours fixing permissions issues on the ReadyNAS. If anyone else is using or is planning to use an x86 ReadyNAS product, you might want to stay with firmware 4.2.5 if at all possible. Don't upgrade until something newer than 4.2.8 is available and you read in the forums that all permissions issues have been resolved.

4.2.7 which I've never run had some serious problems as per discussions in their forum. 4.2.8 suffers some permissions issues still. In an otherwise default setup, shares when accessed at least from a Mac via AFP or CIFS will have varying permissions depending on what "user" you connect with. And it's the reverse of what you might expect.

Guest access will have the most abilities and show less restrictive permissions than the default admin user or any user you might happen to create. Further, files copied to the NAS from Windows and then access on the Mac will show up without write permissions for anyone if using anything other than guest. Using guest will show that the owner can write, but that still won't help and you won't be able to modify the files.

To fix the issue I finally had to set the advanced permissions options for both AFP and CIFS so that the ReadyNAS changes permissions on all new files and folders to Read/Write for everyone. PLus I had to use the Advance tab on each share to also reset the permissions of all files/folders already on the drives to be read/write for everyone.

With these settings in place I can now copy to the shares and access the files/folders from either platform using either CIFS or AFP. CIFS seems to be faster even from the Mac however, so I'm not sure I'll keep AFP enabled for much longer - unless I can come up with another reason in the meantime.

So far the only issue I've encountered that still causes a permissions problem was when using the ReadyNAS to "backup" files from an external USB disk attached to itself. I cancelled the operation and the last folder and its enclosed two files didn't receive the updated advanced permissions. I guess the ReadyNAS changes them after copy operations are complete but didn't do this operation when closing down its copy process. This left me with a folder and two files that I was not able to delete or modify in any way, including changing permissions, regardless of what protocol I used to connect, Windows or Mac. I had to again use the advanced share tab to reset permissions on all files to fix these.

PITA.