Drobo Elite - Ready For The Server Room If Not The Data Center

Posted by Howard Marks
November 23, 2009

Ever since Data Robotics came out with the Drobo it's been the darling of some in the storage blogosphere. While I found the original 4-slot Drobo cute, I didn't understand why serious storage guys like Curtis Preston and my friend Stephen Foskett were so excited about a consumer product. The Drobo Pro, an 8-port DAS array with an iSCSI interface didn't make any more sense. The new Drobo Elite on the other hand seems like a great first SAN array for the SMB market.

I'm not ashamed to admit that I fell into the trap of thinking there wasn't much real technology behind Drobo's pretty face. The package, with its tray-free hot swap drives and LEDs that indicate system status, drive status and even system utilization, is actually wrapped around a set of data protection features that combine some of the best ideas from leading edge higher end storage system that Data Robotics calls Beyond RAID.

The most visible of these feature is the ability to fully utilize drives of different sizes. When you set up a Drobo, you specify single or dual drive redundancy, if you want to be protected against one or two drive failures. By treating all the available disk space as a single pool a 5-drive Drobo S distributes data and parity data across all the drives. I'm sure if you had 40GB drives and a 2TB drive this system would break down, but for reasonable combinations the Drobo just figures out where to stick data to meet your protection level. The only other system I know that can do RAID on different size drives efficiently is Symantec's Storage Foundation, and it's not as efficient as Drobo.

While you can think of dual redundancy as being a double parity scheme like RAID-6 if there's only space on three drives, Drobo will use it for a triple mirror.  It will also mirror or triple mirror when data is coming in too fast for parity or double parity and re-stripe the data later.  Similarly when you swap out a drive for a larger one, which you can do at any time, the extra space is available pretty much immediately and the system will re-stripe later.

Like Atraro's and Xiotech's self healing arrays, Drobo scrubs drives in the background, marking sectors as bad. It also distributes hot-spare space across all its drives, which speeds up rebuilds. In fact, Drobo just uses its free space as spare space, so an 8-drive Drobo Elite that's less than 85 percent full has a hot spare without dedicating space to one.  

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