I’m using Drobopros with Linux (CentOS x86_64) and they work fine, using 8TB LUN size.
See here for getting the initial iSCSI connection running & the partitioning / formatting details:
And here for a couple of tweaks to the iSCSI parameters:
(On Centos, or possibly just newer iscsi versions, the ‘node’ file path is in /var/lib/iscsi/send_targets/… rather than /etc/iscsi )
I’d adjust the parameters immediately after getting the iSCSI connection going, before doing any filesystem work.
Drobo-utils works fine once the iSCSI connection exists.
For debugging, you should be able to ping the drobopro with or without iscsi running, as long as the ethernet setup is OK.
With Centos at least, the iSCSI stuff (open-iscsi) is included, all it needs is the service starting & issuing the correct commands via iscsiadm, as given in the drobo-utils info.