hi sam, can i check if the unmounting and reappearing, and starting data protection mode, all happened on its own without you doing anything, or was this actually after you tried replacing something?
if it started doing that on its own, and it seems to be repeating often, like on a loop, then i think there might be a drive (or drives) possibly encountering some errors (possibly softer errors) a bit like falling out and back into the array, but not fully failing (yet).
can i check if your actual access to the data is still ok currently?
if so, and in case you do not have any backups, i would like to suggest you start taking backups if you can (at least of the most important data), or at least for as much data as you can before it unmounts…
ideally it would be good to raise a ticket with the support team if you can (though i believe a pay-per-incident could still be create in case out of support, if you would wish), though in case the drobo keeps unmounting before you can copy off some of the very large files (which require more uptime to transfer the data), then something else you could try could be
to try putting the drobo into a read only mode, which may help to stabalise the drobo, to at least be able to access and copy off data as a backup, for example as mentioned here:
btw can you remember if your drobo is using single SDR drive redundancy mode, or if it is using dual DDR?
if you do have backups though, (and as long as you are not currently in readonnly mode), and if the drive which keeps indicating a failure, is the same drive (and if it is the only drive that is flashing red, while the other lights are ideally solid green), then you could try to remove the failed drive, while the drobo is on, and to allow dashboard and drobo a bit of time to recognise the change, and then to put in a blank/un-needed replacement drive, and to allow drobo and dashboard some time to recognise the new drive. Hopefully it will then start rebuilding things for you, which may take about 1 day per 1TB of data that you have, depending on the usage of the drobo.