Add drive with Mac turned on or off?


Just got my first Drobo yesterday. I have it running with 3 x 500gb drives which are now about 70% full.

I want to add a fourth drive (1tb) into the empty slot. Should I do this with my Mac turned on or off? I don’t actually want to use the Mac – I’ll be at work – I just want the Drobo to sit and do its stuff.

Also what would happen if I were to install the fourth drive with my Mac turned on, then shut down the Mac before the Drobo had finished its process? Would the Drobo continue working or would it wait until the Mac was turned on again?

Thanks in advance,


It shouldn’t matter if your Mac is on or off when you insert the new drive. Drobo does its thing independently of the Mac, although if you read/write while it is rebuilding, it will slow the process down a bit.

If you installed the fourth drive and then shut the Mac down, Drobo would continue to rebuild. It wouldn’t wait for the Mac to come back on again.

Thanks for the quick reply. Given my configuration above, with about 900gb of data on the three 500gb drives, how long can I expect the rebuild to take when I insert the additional 1tb drive into the fourth slot?

Many thanks,


I honestly can’t say. I have heard wildly varying timeframes for rebuilds. It seems to depend on a number of factors, none of which I understand. :slight_smile:

Based on what people on these forums say, several days is not uncommon.

Thanks again. Much appreciated.


sorry, thats not accurate…

if you just ADD an ADDITIONAL disk - there will be no rebuild - so the “several days” is completely irrelevant.

its only if you were to REPLACE a disk it would need to rebuild the missing data on the disk you removed

simply adding a 4th drive does not involve a rebuild - it will be immediately available and all of your drive lights should pretty much immediately go SOLID green (rebuild = flashing yellow/green).

in order to take advantage of the additional space/speed fully it will (probably) RELAYOUT the data (but this is differnet from a rebuild - at no point will you ever be “at risk” as you are during a rebuild), but it does this totally silently, it wont tell you its doing it, and you wont know when it finishes it. It wont stop your mac or drobo from shutting down/going into standby either, it will just start doing it again when it comes back online.

In fact, due to its black box nature, we cant even be sure it does this - it may leave that 4th drive empty until you start adding more data to drobo - and then do the relayout as part of adding the data, although i suspect this would be ineffiecient so it may not do this, but we just dont know :smiley:

Also DRI do advise that if you wanted to benchmark your drobo you give it a few days to “settle down” after you add/remove drives and get back to s safe state, so its safe to assume it does optimise the data layout in the background, but again, you never really know…

Thanks @Docchris for the clarification/correction. I am sorry for the wrong information. However, I could swear that my Drobo did do a rebuild, not just a relayout, when I added a drive to it. But maybe I am remembering wrong–it was a while ago.

P.S. Nice avatar, @Docchris. :smiley:

Did you insert while it was running? its possible one of your three existing drives may not have been very securely mounted and may have wriggled and momentarily disconnected, triggering a rebuild?

Thanks :wink:

Thanks for all the replies – much appreciated.

For the record, I added the drive and it was available more or less straight away, though there was a lot of noise, so something was going on!


Maybe that’s what happened. I honestly don’t remember. But that seems plausible.