OK, so it’s like forever since I posted about my old Gen 2 & I’ve since upgraded to a 5C, I’m now wanting to head off a potential problem though.
I KNOW the documentation says defragging a Drobo is a no-no, though I got away with it many times with my old Gen2 (which I still have, disused), HOWEVER,
my 5C is being used as backup storage using UrBackup for my family’s computers.
This has resulted in storage of a several million folders & multiple millions of files, all fine sort of 
, apart from the cost in disks, the problem is it also stores fairly massive disk image files in .vhd or .vhdx format. Given the way it sprays data around when transferring via the internet, I’m actually in danger of these images hitting the NTFS limit of 1.5 million extents …
So the question is given I’m also about to create a new LUN & migrate this data to it, do I:
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Ignore Drobo’s advice & start defragmenting?
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Create a new LUN & ignore Drobo’s using Windows to format it with the /L switch to increase the maximum number of extents to ~6 million? Also a no-no as Drobo only advise using Dashboard to format new partitions.
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Raise an actual support request?
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Other? Say ditch Drobo & build a PC to set up Windows storage spaces or Linux LVM instead of my expensive Drobo hardware?
Would setting up the new LUN for backup storage as a fixed size using the “Enable backup” option help or hinder? Or using Windows to format such a volume using 64K clusters to mitigate the limitation as outlined here be useful?
Can the Drobo firmware even handle such workarounds?
I’m really not sure Which way to jump… my natural inclination is to ignore the advice & schedule some defragging to avoid that hard limit… since although intensive it’s still normal “default” file-system activity.
Thoughts??? Shame there’s no emoji for steam coming out of one’s ears!!! 
[edit] Incidentally, how do Drobos interact with/handle NTFS compression &/or Windows server deduplication? I’m considering enabling one/the other or both on the new volume I’m about to create. [/edit]