Single drive failure: replacement not recognized... the usual?

I’ve seen several posts like this on various models and am wondering if I’m in the same failure boat.

Short story: 5 drive (2TB each) on Drobo S. Everything working smartly until a few days ago. Bay 4 goes flashing red. Identical replacement purchased. Removed Bay 4 drive. Replaced with new, identical drive. Drobo dash still says “Add New Drive”. Waited a while… Nada. Reseated the drive a couple of times. “Add New Drive” light still showing.

Now… I see the “space free” on the dash slowly getting less and less as it winds down (I had 3% left, now 2.99%, now 2.94%, et. al.). Is this the “rebuild”? I was under the impression that lights were supposed to show as orange and that there would be a timer of some sort. Nothing I’m experiencing bears any resemblance to various videos/posts on how it’s all supposed to go.

Should I wait and see?
Should I restart the Drobo?
Anyone had a similar experience recently and successfully recovered?

Right now, I’m feeling pretty low. First time drive failure and DRobo not functioning “as planned”.

hi, usually if it is rebuilding it will take about 1 day per 1tb of data that you have (so if it is still rebuilding i would wait for it to finish)

but is it actually rebuilding? … can you see any other info in dashboard, and can you see if the physical drobo bay lights are flashing / blinking and which colours they and other lights are showing?

if the free space is shrinking, can you check if any other programs are using the drobo?
(one way on windows could be to download process explorer (sysinternals) and to run a handle/dll search for your drobos drive letter. such as “f:” without quotes if your drobo drive letter was f
(this would list all the open files for reference)

(if its any consolation i have upgraded several drives before, and have also had a failure to which it recovered) though if you have any more info on how you did the removal or replacement, such as was power off at the time, it could be useful.[hr]
one other thing to note though, is that i think the drobo needs at least 5% free space to do a rebuild, ideally more if possible, and if it goes to 95% full it goes into a slowdown mode and that could also be slowing things down in general too.


Thanks for the reply and all the helpful information. Definitely some food for thought.

RE: Is it actually rebuilding?
My conclusion is: NO, it’s not. No lights change, nada. Drive light solid red, asking to add a new drive (with new drive in slot). Multiple reseating attempts at the outset resulted in no change.

RE: Free space shrinking…
Freed up around 4% and, by this morning, it was at 0 bytes again. Only thing running is Plex server (which I’ll be sure to shut down next time I free up space today)

RE: 5% needed for rebuild
I guess I’ll have to do this. I can certainly delete enough data to accomplish it without issue.

RE: How I did the replacement
I replaced the drive “hot”; that is, while the Drobo S was on, I ejected the drive that was blinking red. Then I inserted a new one. That’s it. Basically, I followed the video found at Drobo for the S series and replacing onboard drives.


1.) Assuming I clear more than 5% space, what should I do next? Is it better to shut down the Drobo and replace the drive cold, THEN turn it back on?

2.) What – in your opinion – is the most valid step-by-step method for getting the rebuild to actually function?

Again, thanks for all the excellent information.

hi thanks for more info,

hot swapping a failed drive is the usual way to do it, especially for an identical model
(other models or newer ones might need a firmware update 1st but i think lets leave a firmware update out of this picture for now)

when you say plex is running… is this an app on the drobo? (it may just be a computer app, indexing files on the drobo-s, but just wanted to check in case you had a NAS model instead of a drobo-s) :slight_smile:

i would disconnect from the internet, disable any antivirus etc, and stop as many programs as you know you dont need. no itunes helper or other stuff like windows search indexer etc :slight_smile:
then i would see if the free space is still shrinking. if it looked stable, i would try to copy/verify/delete some more files up to say 94% at least to be free, ideally 89% free, and then would wait for dashboard (and physical drobo) to slowly reclaim the free space to that level (i say 89% as that should free up a blue led indicator if i understood how they work correctly)

then, i would wait to see if the drobo starts to do the rebuild on its own (another hour at least), and if not, i would shutdown drobo from dashboard and power off the computer, and then would uplug the computer connection cable from drobo before powering up the drobo on its own, to see if it goes through the usual boot up led sequence, and then starts rebuilding on its own.

(thats just me, and if it still did not rebuid, then there are more steps to take, but probably better to discuss those as things progress in case they need tweaking accordingly) :slight_smile:


Excellent info I can use once again. Much obliged.

Well… here’s the overall situation.

I shut off all processes/services (including the Plex Server software I referred to earlier… It’s a service; this isn’t an NAS system). No AV, nada. Just Drobo. Deleted 40 GB to make some room again, just for a test. Watched it slowly count down to… you guessed it… 0 bytes.

[color=#FF0000]Additional note:[/color] either I didn’t notice it before, or it just manifested itself. I now have TWO errors on the Drobo dashboard (the second one only accessible if you press a down arrow in the error window). The first error is, as stated before, to add a drive. The second states that I need to install a larger capacity drive to ensure single redundancy or TWO larger drives to ensure dual redundancy.

Pic of Drobo error/status

Here’s my surmise, so tell me what you think. I think that:

a) the eating up of recently freed up space is being done by Drobo as some ancillary routine associated with “rebuilding”.

b) the first thing I should try is to free up at least 5% as you mentioned, then shut down and restart the drobo (and connected PC) to see if it “triggers” a real rebuild.

c) Optional: remove the new replacement drive prior to shutting down? Yea/Nay? Any thoughts?

d) Optional: should I really get a 4TB to replace the 2TB drive I just purchased for a replacement? Yea/Nay?

d) Optional: should I update the firmware? It’s currently at: 2.1.5 [5.41.62910]?

So far, no change but a continuous loss of free space with only DRobo running. I should note here that this is a dedicated PC/server (Win7) that has never had anything installed on it except Drobo software, the Plex server software (which is easily terminated and only serves media) and AV (Avira,… also easily terminated unlike most bloated AV suites). It’s never been used for anything else.

I should also state that I find the eaten space somewhat perplexing as – prior to the drive failure – I still had nearly 18% free (with single redundancy). It’s all so weird, but I’d sure love to get it to work.

hi, with a friendly starwars reference, “i find your lack of '‘space’ disturbing” :slight_smile: (or in your case, perplexing) :smiley:

jokes aside though, and for your a) and b) i dont remember seeing free space suddenly start dropping but i think freeing up more space is good to allow the rebuild to take place.

one thing to check though, would be to see in the (tools) section i think, just to confirm if your drobo is in SDR mode (and not ddr) - if ive done the maths properly, then your initial 5x2tb = 10tb raw (-2tb failed drive) = 8tb raw (-2tb for sdr) = 6tb raw (x0.9) = 5.4tb usable approx

As your data is still currently available, and rather than deleting files to make space, do you have a backup of things that are on the drobo? if not, it might be a good idea to backup while things are available, if you have a way to do that, (or at least for the important stuff) and then to delete some more files to free up space.

(i remember when i put a new drive into my gen1 or gen2, i did have to fully exit and fully restart dashboard, so it might be worth trying that too)

for c) probably nay for now :slight_smile:

for d1) you (could) get a 4tb, but i dont think you would gain any usable space unless you also had a 2nd 4tb as well.
for d2) v2.1.5 seems to be the latest (main version) version.

(i split your double d into d1 and d2, not that theres anything wrong with a double d) :slight_smile: