Dual Disk Redundancy & misleading messages

I’m writing this to alert others to a potential problem that if left alone may resolve itself. I experienced this with a Drobo 5N, but it may apply to other models as well. There are some other threads here that may indicate that others have encountered the same or a similar problem the past.

I have a Drobo 5N containing 5 4-TB WD Re drives. It’s connected to two Macs via an ethernet router.

At one time this Drobo had almost 10 TB of data, but after some housekeeping I reduced that to 7.88 TB. Since I expected this level of use to remain constant for a considerable period of time I decided to switch to dual disk redundancy. I did this using the Drobo Settings in the Dashboard. Then the fun started:

  1. Initially all 5 drives had a health of Good and the Drobo itself had a health of Good.

  2. A few minutes after switching to dual-disk the health of the Drobo switched to Critical and the status light for bay 0 turned to solid Red while the health of the drive in bay 0 stayed Good. The following message was displayed “Drobo cannot protect your data against hard drive failures until you provide at least 2 hard drives for single disk redundancy or 3 hard drives for dual disk redundancy. Replace the hard drive indicated by the red light with a larger capacity drive to enable Drobo to protect your data against hard drive failure.” This did not make sense because with dual disk redundancy and 5 4-TB disks I have 10.69 TB of available space and only need 7.88 TB.

  3. After about 30 minutes, the status lights off all the drives went to blinking green/amber and the Data Protection warning appeared. This was what I expected.

  4. After about 2 hours of data protection (much less than expected), the status of the Drobo changed to Critical, the status light for bay 1 turned to solid Red and the health for bay 1 changed to Warning. The same confusing message reappeared.

  5. After about an hour with no change in status I removed the drive in bay 1 and replaced it with an old but clean 4-TB WD Re drive. This was probably a mistake. Shortly after I did this the Drobo entered a seemingly endless loop. It would sit in the Critical model with the confusing message for 10-15 minutes, then enter Data Protection mode for 1-2 minutes, and then return to the Critical mode.

  6. After 12-16 hours of cycling from Critical to Data Protection, I removed the disk from bay 1 and changed the Drobo back to single disk redundancy.

  7. For about 8 hours the Drobo remained in Critical status with the status light for bay 1 solid red and bay 1 marked “Add a drive” on the Dashboard.

  8. At the end of the above period the Critical/Data Protection cycle resumed.

  9. After about 2 days (yes, days), the Drobo stopped cycling and entered Data Protection Mode.

  10. After 2+ days the Data Protection mode ended and the health of the Drobo changed to Good.

  11. About an hour later, I reinstalled the replacement 4TB drive in bay 1 and again changed the Drobo to dual-disk redundancy.

  12. The Drobo properly went into Data Protection mode. At this time I noticed that the status of the drive in bay 2 had changed too Healed. I also noted that in addition to the Data Protection message a second misleading message reading “Drobo has detected a failed or removed drive. Your data is now protected from only one additional drive failure. Please add or replace a new drive soon.” was displayed.

  13. After 2 more days the Data Protection finished and the Drobo now appears to be operating properly in dual disk redundancy mode. Bay 2 still shows a health of Healed, but all lights are green.

During all this time both Macs were able to update TimeMachine information stored on this Drobo. During this time, my home suffered a brief power failure, but the Drobo is plugged into a UPS and I don’t think that had any effect, but I wasn’t present at that time.


  1. I probably should have just left the Drobo alone to do its thing for 4-8 days and not gotten spooked by the messages I was seeing.

  2. There was probably nothing wrong with the drive in bay 1. This is supported by separate tests I ran against it after I removed it from the Drobo.

  3. During the Critical/Data Protection cycle the Drobo was probably doing some repairs or preparing for real data protection, but the message displayed made no sense.

  4. The firmware/Dashboard does not do a good job of informing the user about what is going on for the situation I encountered.