After spending a day trying various things I seemed to solve this by changing the sector size.
Setting the Storage Spaces sector size and StarWind VSAN virtual disk sector size to 4096 was the key.

Now lets see if I can get the lab running

Hi, Hi Ekowc, if you are using a free version, only SMB or NFS will work. You cannot use these HA devices as true iSCSI targets. As far as I have understood you have to make a iSCSI connection on the VSAN nodes, then share the disks via SMB. I've manually edited your post and had removed URL to Visu...

Hi, I have setup a two node VSAN cluster. Both nodes are running Windows Server 2012 R2 and have Storage Spaces RAID0 to store data (yes I know its not recommended). Every time I launch the iSCSI connection the on either of the nodes the synchronization drops due to IO operation failed. Creating a d...