Confused about "Protected Space"

Forum History General Discussion
1

I have had my Drobo 5D for some time, and never had any issues. I have: slot 1 - 3TB drive
slot 2 - 3TB drive
slot 3 - 3TB drive
slot 4 - 4TB drive
slot 5 - empty
msata ssd 120GB
If it click on Drobo Dashboard - “Capacity” I get:
8.12TB available for data
931 GB reserved for expansion
2.77 TB used for protection
14.32 GB overhead
When I click on “Volume” I get:
7.58 TB used
16 TB Maximum capacity

Windows shows the Drobo drive has 8.41TB free space.

So, my question is, I get a yellow warning: "Drobo is running low on protected space. Insert new drive in empty slot.

I’m OK with doing this, and have a new drive on order but why is that needed if I have 8TB available with my current configuration?

THANKS!

After I posted this, I clicked on Drobo Dashboard “list” icon. It states:
capacity - 8.12 TB
used - 7.58TB
free - 559GB
I’m guessing this is the reason it needs another drive…???

2

Welcome to thin-provisioning, which gives the appearance of having more physical resources than are actually available.

The usable space Windows “sees” is your 16TB volume (your 5D is capable of a maximum 32TB volume which you select during initial setup). Your “actual” capacity is determined by adding your drives and subtracting the largest one. Thin-provisioning is what allows you to increase capacity by adding larger drives without re-formatting and starting over with each change.

3

hi just to follow on with what dragon said above,
if you also use DDR in future, then it will take up the capacity of 2 of your largest drives (since its then allowing for up to 2 drive failures)