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Strange capacity warning 5C - Printable Version

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Strange capacity warning 5C - jubeth - 05-14-2017 05:06 AM

Bought a Drobo 5C a month ago, set to have dual disk redundancy, and populated with
4x 1TB HDD (different brands/models)
1x 5TB HDD
Sure, a strange combination, those are all spinrite recovered drives from older systems, and they all are still perfectly fine according to spinrite.
Now, it got fuller the past week, so I understood why 1 of the 1TB drivebay leds started turning yellow due to 'running low on protected space'.

So I replaced the 1TB bay that had turned yellow with a 4TB disk I had left from a recently upgraded system somewhere.
The drobo took 3 hours to have it implemented in its beyond-raid.

Assuming the extra (newly added) 3TB would make some more space available, give some room, it disappointingly did not! Very much to my surprise. No idea what kind of RAID this is, but adding 3TB to a 5-bay RAID would *at the very least* make the system all-green again. Especially after 3 full hours of re-syncing the raid.
Now another one of the left over 1TB HDDs has the yellow LED, with the exact same capacity warning.

I did not expect this for this price, to be honest. This has me thinking about returning/selling this drobo, and replacing it with something else..

I did some calculations and for the same price I could easily buy 2 new 5TB drives, mirror them in a new 2 bay raid box and have practically the same security feeling as I do with this 5C. The chances that 2 new (spinrite tested) disks fail at once in a new 2-bay unit are lower than 2 disks failing at once in this old disks in my 5C. Plus it's a lot faster using 2 bay mirror raid, easier to recover when the unit itself fails too.
I wonder how I fell for this drobo trap.


RE: Strange capacity warning 5C - Paul - 05-15-2017 05:37 PM

hi jubeth,
i think what may be happening is that your drobo is using space on the smaller drives, to protect the larger 5TB from failing, and that while you are using a mixture of drive makes and sizes (which is fine to do), it is just that yoru drobo may not be having the most optimal configuration currently.

for example, all drobos tend to have a default SDR mode for single drive redundancy, and in order to protect your 5tb from failing, it probably had to spread it across the other drives, and reserve a bit for the future.
i think that even with the recent 3tb that you upgraded into, it would still also be trying to protect the 5tb drive.

if you are able to upgrade another 1tb into a 5tb, i think you could end up with the following:
5tb + 5tb +3tb +1tb +1tb = 15tb (raw capacity)
15tb (-5tb for sdr) = 10tb actual
10tb (*0.9 for usual filesystem overheads) = approx 9tb usable

btw can i ask how you can do a spinrite on 5tb drives? as far as i knew it could only go up to a certain point, which another user mentioned here in the past, i think around 2tb drives? Smile


RE: Strange capacity warning 5C - AzDragonLord - 05-16-2017 05:05 AM

Jubeth,

What you saw is normal. With dual-disk redundancy enabled you want to add up all your drive capacities and SUBTRACT your two largest drives. What remains is your USABLE capacity. If you use single-disk redundancy you would SUBTRACT just your largest drive.

Sometimes, like in your case, replacing just one disk with a larger capacity only adds to your "reserved for expansion" totals instead of "used for protection" totals.


RE: Strange capacity warning 5C - Paul - 05-17-2017 12:38 PM

(thanks dragon, i forgot the sentence about ddr) Smile