I have identified this issue with the DroboFS, but it may exist in the Drobo family as a whole.
The 5 disk array consists of 3 x 2Tb drives, and 2 x 3Tb drives. There is 2.34Tb of data on the Drobo.
If I eject (‘fail’) one of the 3Tb drives then after a few seconds of yellow/green flashing, the 4 bays revert to green, and the empty slot to solid red.
This leads me to think that my data is safe, but that I should add another drive to increase storage.
However, if I eject the other 3Tb drive, everything goes red, restarts, and stays red with no access to data.
Looking at the Drobo Calculator, 3 x 2Tb drives should yield storage of 3.63Tb - and I only have 2.34Tb on there.
Is it - and I am just guessing here - that Drobo ‘scales up’ when larger drives are added, but fails to ‘scale down’ when drives are removed?
If so, this does not seem the best way of doing things. It would mean that potentially a drive could fail, as I simulated above, be told by the Drobo that all my other drives were fine and my data was protected but should another drive fail, I would be left with no access to my data unless I went out and bought another hard drive.
Dual disk redundancy is OFF - am I misunderstanding its concept? I thought it was to protect against two SIMULTANEOUS failures, not a later failure when all lights are green on drives.
I would just emphasis again - there is only 2.34Tb of data in there - well below the max storage capacity of the 3 x 2Tb drives remaining.