Drobo

Dual Disk Redundancy Capacity Question

Hi.

how much free space do you need to have on drobo before you can turn on the dual disk redundancy option?

OBVIOUSLY it would be at least another 1 x your largest disk just for capacity reasons, but that would give you a drobo 100 %full - so can you only turn the option on if you would have say at least 15% free AFTER You turn on the option?

For example:

8 x 1TB drives - single redundancy give 7TB available for data (im going to ignore the stupid round for the sake of this example)

now obviously you need another 1TB disk for the dual disk redundancy, so it is physically impossible to turn it on if you have more than 6TB of data on there

if you did have 6TB exactly and were able to turn it on (you are not) then the resultant 2 disk redundancy disk pack would be 1005 full which Drobo wouldnt be happy with.

so is it that you cant turn on dual disk redundancy if the resultant pack would give a capacity warning ?

i am guestimating that you must have less than 85% of the dual redundancy disk pack’s capacity’s worth of data?

so in my example the 8TB drobo with single disk redundancy, can only be converted to dual disk redundancy if you have less than 5.1TB of data on it (85% of the 6TB available in dual redundancy mode?)

oddly i cant find this documented anywhere, hopefully jennifer can give us the official answer as to what capacity the “dual redundancy” check box becomes available - my drobo is stuffed and im taking data off it to put it back to dual disk redundancy)

It’s not a matter of how much free space you have rather than how many drives you have. Dual disk redundancy takes a minimum of 3 drives in the DroboPro before you can enable dual disk redundancy.

and i have 8… now down to 7… !!!

of course its a matter of free space!

assuming all your drives are the same size…

if you have 8 drives and single redundancy - then you can put 7 drives worth of data on it more or less.

if you have 6.5 drives worth of data then converting to double redundancy is physically impossible

its all to do with whether you have enough free space to sacrifice another drive to a second layer of redundancy[hr]
if you had 8 x 1tb drives, and put 5.8 TB of data on it, in theory you could convert to double redundancy since that would give you 6tb of storage space , but drobo wont let you… because then the resulting array would be "too full (about 95%),

so my question is what level of “fullness” does drobo deem acceptable for the resultant array to convert to dual redundancy at, is it 85% (when 1 yellow light would usually come on) ???[hr]
Just to clarify what you told me…

In order to enable DUAL DISK REDUNDANCY… i have to have TWO DISKS, which are REDUNDANT…

i think i may have worked that one out all by myself you know…

jennifer care to shed some light on my actual question?