Adding last drive seemed TOO fast. Why?

I have 4-bay Drobo. I was using 2 drives. Last night I added a THIRD drive and it took 2 hours to ‘build’ the new drive, blinking yellow/green until finished. This morning, I added a FOURTH drive and it instantly had a GREEN light, and Status showed Good & healthy. There was NO ‘build’ time. All drives are 1TB Seagates. Is it normal that the fourth drive was instantly GREEN?

hi philca, can you remember or check how much data you have on your drobo currently?
(usually it takes about 1 day per 1TB of data)

it is possible to add a drive which shortly afterwards becomes recognised by drobo and solid green. This assimilation of the drive into the diskpack, is usually followed by some internal/background processing where the data gets shuffled around for increased overall protection using that drive.

(there have been a few feedback posts recently regarding the feature request to have this info popping up on screen, so that users are made a bit more aware, though you should be ok to use your drobo and save files to it even if you didnt see a rebuild)

For the 1st rebuild that you saw, it could be something to do with the way the data protection mode works (going from 2 drives, to having data split across the 3 drives…and if you were to have a lot more data on the drobo than 2 hours worth of usual rebuild time based on the 1 day per 1TB of data, then it may just be that switch, but if you can post back when you get a moment it would be interesting to see)

Hi philca,

I had the same behaviour on my old 4 bay Drobo when I increased my original 3 disk pack to 4 disk. I never had an issue (although I also never had a failure of any disk in the years I ran the unit, in fact the same unit and disk pack is no being used by my sister and keeps on ticking)

My simplistic view is that the Drobo with a 2 Disk Pack, simply keeps each full packet on each disk so if one fails the other still has a full copy. When you add the third disk to the pack it calculates a checksum for each packet and places it on the third disk (which is why the rebuild seems faster than when you have a disk failure issue).

In this sate, if either of the disks with the full packet fail the Drobo can rebuild and use the checksum to validate the result. If the checksum is lost it rebuilds it from the full packets that still remain.

When you then add the fourth disk to the pack the Drobo doesn’t need to do anything to improve the current data’s status. Hence the drive is simply added. The Drobo will start to use it with new data going forward.

Well, that’s my thinking and explanation anyway. I early on decided that I liked that the Drobo was for the most part a Black Box and I don;t need to concern myself with exactly what it’s doing. I simply need to accept that its doing its job and trust that when the inevitable happens I will come out the other side better than I would have without it.

Thanks for the useful information! I helped your advice!