In my first review of the DroboPro, I was somewhat disappointed that I couldn’t access the ‘Pro from the Drobo Dashboard when the device is serving out iSCSI LUNs across the IP connection. This restriction is a serious flaw, as it requires taking the DroboPro down and off the network in order to connect to a PC running the Drobo Dashboard. However, I’ve found a workaround that allows me to run the Dashboard *and* present iSCSI LUNs at the same time. Here’s how…
Firstly, let’s review my configuration. I have a DroboPro that connects to my main ESXi server. It presents eight 2TB thin provisioned iSCSI LUNs to ESXi. These are then used as datastores or can be used for RDM devices. It’s the use of RDM devices that proves the answer to the problem. An RDM (Raw Device Mapping) device isn’t emulated by vSphere/ESXi as a standard vmdk would be. ESXi passes all I/O directly to the LUN, simply retaining a pointer reference to it on an existing datastore. I’ve used RDMs in the past to virtualise storage management servers (for example EMC’s Solutions Enabler) where the software talks directly to a LUN on the storage array using bespoke non-standard SCSI commands. It appears that the Drobo dashboard also uses bespoke commands to connect to the DroboPro when only the iSCSI IP link is available. Fortunately, RDM honours these too, so the DroboPro can be administered through the iSCSI LUN using it as a command device.
So, to administer your DroboPro:
- Create a dedicated iSCSI LUN on the DroboPro using standard techniques. The LUN can be created as a minimum of 1TB, however as its virtual, the LUN will occupy only a tiny amount of real physical space.
- Assign the iSCSI LUN as an RDM device through ESX/ESXi to a Windows host. Format the LUN on the host.
- Install Drobo Dashboard on the same Windows host. Voila!
It may well not be necessary to create a dedicated LUN, as I tested this theory using an existing server that had a DroboPro iSCSI LUN already assigned to it. There’s one thing to be careful of though. Remember if the virtual server you’re running Drobo Dashboard on is configured from LUNs on the DroboPro, you need to ensure you don’t affect those LUNs otherwise you compromise your management station.
Finding this workaround makes me feel happier about using the DroboPro in an ESXi/ESX environment. I’d still recommend creating all the volumes you need on the DroboPro up-front before you start using it with ESX, however at least now there’s a way to monitor the device without relying only on the external lights.