Do I have to do dual disk redundancy to remove one of five drives?
If I remove the 1.5TB permanently and only wish to use the 4x1TB HDD will BeyondRAID recognize the 4 drives and give me single disk redundancy?
Are you saying I should do dual disk redundancy because the drobo may not rebuild/adjust?[hr]
I will do what you say, logically if something bad was to happen to one of the 1TB’s while removing the 1.5TB. Then it is the wiser procedure to follow.
I think with four 1TB drives and a 1.5TB drive with ~2TB stored you are at the point where dual disk redundancy won’t be possible after the removal of the 1.5TB drive. Assuming that you lose the capacity of two 1TB drives to provide redundancy you are only left with 2TB of usable space. If it allowed this configuration, this would put the Drobo into the place where it slows down to prevent overfilling, and the rebuild process may have problems, or as @docchris says it will anticipate the issue and drop back to single disk redundancy only.
1TB drives can be had for ~$60 and 1.5TB drives for ~$80. Given the inconvenience, the (albeit small) risk to your data during the heavy drive activity during rebuild, and the probably 24hour+ rebuild time during which time your Drobo will be very slow, if there’s any chance you could spring for another drive either to replace the one in the Drobo or to put into your PC I think you would be much happier…
i was saying more that you should have enabled dual disk redundancy - because then when you pull one disk - you are still protected against a second failure.
if you have single disk redundancy, and pull a disk… then you are no longer protected, so if another drive fails during the rebuild, poof! its all gone. and you remain vulnerable until it has finished the rebuild.
changing to dual disk mode does not leave you unprotected at all - its ADDING another layer of protection - you are still protected against a single drive failure (otherwise i wouldn’t have advised you that upgrading to it was a good way to protect yourself!)[hr]
Once you have achieved your dual disk redundancy and its showing “your are protected” you can pull your drive - and then it will say you are unprotected - but it means you are unprotected against double failure - you will still be protected against a single failure (since you selected dual disk redundancy and have only failed one drive by removing it)
ideally it will start to rebuild automatically to being dual redundant on your remaining drives, but you may not have enough space.
you should therefore be able to select single disk redundancy and it will initiate rebuilding to a safe single redundancy state on your remaining drives
There are three possible outcomes when a drive is removed:
Drobo will go into relayout and “downsize” the available storage to go back to the fully-protected state (DDR or SDR).
Drobo will not go into relayout and will be in a degraded protection (DDR) or unprotected (SDR) state.
Drobo will tell you too many drives have been removed, the storage will go offline, and it’ll blink red at you until the drive is reinserted.
Which of the three happens depends on how much data you have stored on your Drobo and how much data a fully-protected Drobo without the removed drive would be able to hold. In none of the cases would data be lost, unless #3 happens and you cannot replace the removed drive.
In your case, since there would not be enough space to “downsize” it’ll simply go into degraded protection DDR (essentially SDR) state, since you have DDR enabled. Case #2 above.
You will not have less usable storage, you will still be able to access your data, and you will still be protected from one drive failure.