I have a 3rd Generation Drobo-S fitted with 5x 2TB Western Digital Green, currently configured with dual failover and providing 6x 1TB virtual volumes.
It's connected via an eSATA cable that's rated at 600Mb/s, to a Dell PowerEdge R210.
The R210 is connected to another PowerEdge & exports the Drobo volumes as NFS shares over a 20Gb SAN.
What I've found is that no matter how much effort or time I spend in attempting to resolve throughput issues to those volumes, there's no hope to be able write to the Drobo at >60 MB/s.
Sometimes it'll burst up to 250, but for the most part it's dog slow, usually between 10-20 MB/s.
As such, I cannot use it for much more than archiving backups- not for housing Virtual Machine images as was originally intended.
Another thing I noticed is that when changing the filetype of the backups, it'll grind to a crawl, causing I/O delays that are usually steady at zero to skyrocket up to over 15%, until the previously used filetypes are stale & deleted.
For example, I have vzdumps that can be compressed or not. If I toggle it, the backups take more than twice as long until the older ones are replaced and all are the new format.
When I asked Data Robotics support about the possibility of their sparse provisioning mechanism remaining functional with the ext3 journal offloaded to a SSD, they dismissed the question entirely as soon as they heard 'linux'.
Basically they told me to F off, citing that the linux dashboard application is unofficial, despite the fact that it's completely unnecessary & has never been used on this device.