I hope this helps someone else...
OMV installer attempts to create a swap partition equal to the amount of system ram by default. If ram>available space, the installer fails.
-Pull out all but minimum system ram
OMV doesn't need much disk space and I have a bunch of smaller unused USB sticks lying around (8gb) BUUUT my minimum ram configuration is 8gb.
-Load Deb then build/load OMV
Original thread I found suggested netinst img.
-My method: Install on a sufficiently larger USB stick then transfer partition to smaller stick (I have 64gb ram so I used a 128gb stick)
- Install as per usual onto larger stick
- load OMV extras/ramdisk plugin, restart / verify operation (swap partition should show as 'unmounted')
- burn GParted image to CD or USB stick and boot (make sure you grab amd-64 image)
- resize data partition to fit smaller USB stick (overprovision a bit, ie 7.25gb on 8gb stick, many reasons for this)
- delete any existing partitions on smaller stick
- copy data partition from larger stick onto smaller stick
- after these operations have completed, add the 'boot' flag to the newly transferred partition
- test functionality - this may not always be the case but I had to install bootloader as well
- guide for bootloader here (Restoring GRUB 2 Boot Loader)
- repeat procedure on a third stick... Might as well make a backup (or 3) while you are at it.
This method should also work for migrating from a disk install > USB or spinner>ssd etc.
references to other threads