Survival of multiple drive failure


I have a drobopro - Its currently setup with 3x1.5TB drives plus 3x1TB drives, dual redundant - which is 7TB total capacity, 4TB available. I have 2.3TB of this space
“in use”.

While I was setting the system up, I was replacing a 500GB drive with a 1TB drive - I accidently knocked out one of the 1.5 drives. The drobo and data survived of course (it took about 15 hours to recover, after replacing the drives) - but i noticed when i knocked out the 2nd drive, the blue lights went up from about 60% usage to about 80%. Then down again when the drives were inserted.

This got me thinking - if the drobo is “data aware”, and moves data around as required for raid redundancy - surely then its possible for the drobo to survive multiple drive failures beyond the 2 failures already allowed for in “Beyond Raid”.

For example - say I upgraded my drobo to 3x1.5TB+5x1TB drives by slotting in an extra 2 1TB drives in the spare bays, but retained the same current data usage (2.3TB)

Just say all 5 1TB drives - and even one of the 1.5TB drives as well - failed over the course of (say) a week. Would the drobo and data survive?

I think - given enough recovery time after each failure - it would! If so, it indicates that if you have a drobopro - it makes sense to fill it to capacity (ie, use all 8 bays if possible), even if you use much less space than that is available.

Any thoughts? .


Robert, there are conditions where Drobo or DroboPro can protect your data from multiple, sequential drive failures. The factor that determines if this is possible is whether the unit has enough available space to rebuild from the first drive failure. The Drobo will have to complete its rebuild before it can protect against a sequential failure. For DroboPro, if it is set up to protect against two drive failures, then if one drive fails and the unit starts to rebuild you are protected against a 2nd failure. Once the DroboPro finishes rebuilding you might be able to survive a third drive failure if there is enough space. In general, if the LEDs are green it is always possible to survive a drive failure.