The supported OS is the Yocto image that you can download here :Galileo Software Downloads. The issue that you are having it could be related to the drivers as you said.
1. Could you tell us which image are you using right now in your board (Yocto, Debian)?
2. Did you installed some drivers in order to use iSCSI or you are just using the default packages in your image?
I found this website with instructions and requirements for the installation of the drivers and recognition of the devices. Take a look at the Download Section, you could find the packages you need in there.
I don't know if you already use those links but let me know if are helpful for you and all the advances that you get doing this.
1. I'm using galileo-debian | SourceForge.net since it ships with a VM and a good guide on how to build a image with custom drivers.
2. I've found the problem, I've not included the following into my image:
Device Drivers --->
SCSI device support --->
<*> SCSI disk support
[*] SCSI low-level drivers --->
<M> iSCSI Initiator over TCP/IP
I'll give Yocto a try once I've understand how to customize it to work with iSCSI and g_mass_storage. I'm curious if it offers better performance since the LAN adapter seems to max out at about 700kB/s. I assume it's correct that the orange LED on the Ethernet port is always on?