Replacing drive in Drobo


I have a question about replacing a drive in my Drobo.
My Drobo has 4 bays and I have 4 1TB harddisks in it.
Recently the top drive got a red light and the dashboard said i had only 10% free space.

I then took the drive out and inserted a brand new 2TB disk.

All lamps started to flask orange/green as the Drobo was working. According toi the dashboard I should leave it to work for 40 hours (can this be true?).

Anyway … the 40 hours has now passed, and guess what?

Now the dashboard says I have only 3% free space (and i haven’t copied anything to it since I replaced the drive) and that I should replace harddisk no. 2

See picture here http://gallery.me.com/peterr#100249

So now I am really confused - i had hoped I would get more space by adding a larger drive.

Does anobody have similar experiences? Is this normal? Did I do anything wrong?

Kind regards,


Hello Peter,

check out Drobo Calculator and you will see what happens when you replace a 1 TB drive with a 2 TB drive


Aha … I see … nothing happens. But how can my free space go DOWN from 10 to 3%? That is weird.

I’ll add another 2 TB drive.

I am using Western Digital Caviar Black and i haven’t got a clue what the color codin means. I hope the drives are reliable.

you are correct in that the free space should not be reduced, it should rebuild onto your new 2tb drive and give you the same free space as previously.

the good news is as soon as you a second 2tb drive - then you will have 1tb free space

OK. I have just added a second 2TB disk, and now I have to wait another 46 hours … but, yes, it apparently gave me an extra TB


And your next two 2tb disks will each give you an extra TB.

I know it seems a long time but if You actually think that its recreating 1TB of your data, by performing calculations on the remaining 3tb of data, its actually very impressive!

I’m absolutely thrilled that it works … but terrified by the thought that someone might try to dump some data on it wjil it is working …

Correction … I dont have to wait another 40 hours. Apparently I have to wait for another 196 hours … what’s going on?



Sometimes the time will fluctuate then settle down to a correct time frame.

And why are you terrified that someone might put data on it? It will work normally, the rebuild will just take longer.

If You are that concerned, just power down the PC it is attached to then disconnect the data cable (so You can then carry on using that machine. Drobo will finish rebuilding uninterrupted :slight_smile:

Aha … I learn all the time. So nothing bad will happen even if someone decides to copy data to it while it is rebuilding. That’s reassuring. Thanks, I can sleep much better now.

That is correct, you are completely able to read and write to it while it is rebuilding - thats half the benefit of it,

however… while it is rebuilding you are most definitely AT RISK of a drive failing (but all regular non-raid computer drives are also at risk all the time and lots of people don’t worry about that), so a lot of people will minimise the activity they do on their drobo, since this will make your at risk period longer as read/writing to it slows down its rebuild.

Whoa … it’s done and I’m protected! Life is good!


Yay!! :smiley:

glad to hear it :slight_smile: