LaCie 2big USB 3.0 and upgrade to Mojave

Hi,

I'm just upgrading my Mac Book Pro (Early 2015, Retina, 13") to Mojave from Yosemite - yes bit of a leap. I've gone for a clean re-install - lots of old crufty stuff accumulated over the years so going for a big clear out. Mojave has installed fine and I've upgraded from the installer version to 10.14.2.

The problem is that it absolutely refuses to have anything to do with my backup drive, which is a LaCie 2big unit connected via USB 3.0, configured as RAID 0.  The drive is in the USB tree (output of ioreg below) and it does work - I've got a bootable clone of the Yosemite drive on it that works just fine as a startup disk.

Any thoughts? This seems to have happened a lot with these drives and High Sierra and Mojave. The system is pretty bare - not reinstalled anything yet so a software incompatibility seems unlikely. It also doesn't seem like a cable issue since the same cable works fine when I boot from the Yosemite partition on the big2 drive. I can't find any obvious links to a Mojave driver or firmware requirement.

Thanks,

David

lb-dormelap:~ dorme$ ioreg -l -p IOUSB
[snip]
    +-o 2Big Quadra USB3@14200000  <class AppleUSBDevice, id 0x1000007e8, registered, matched, active, busy 0 (2 ms), retain 17>
        {
          "sessionID" = 29459483735
          "iManufacturer" = 2
          "bNumConfigurations" = 1
          "idProduct" = 4191
          "bcdDevice" = 1
          "Bus Power Available" = 250
          "USB Address" = 2
          "bMaxPacketSize0" = 64
          "iProduct" = 3
          "iSerialNumber" = 1
          "bDeviceClass" = 0
          "Built-In" = No
          "locationID" = 337641472
          "bDeviceSubClass" = 0
          "bcdUSB" = 528
          "USB Product Name" = "2Big Quadra USB3"
          "PortNum" = 2
          "non-removable" = "no"
          "IOCFPlugInTypes" = {"9dc7b780-9ec0-11d4-a54f-000a27052861"="IOUSBFamily.kext/Contents/PlugIns/IOUSBLib.bundle"}
          "bDeviceProtocol" = 0
          "IOUserClientClass" = "IOUSBDeviceUserClientV2"
          "IOPowerManagement" = {"DevicePowerState"=0,"CurrentPowerState"=3,"CapabilityFlags"=65536,"MaxPowerState"=4,"DriverPowerState"=3}
          "kUSBCurrentConfiguration" = 1
          "Device Speed" = 2
          "USB Vendor Name" = "LaCie"
          "idVendor" = 1439
          "IOGeneralInterest" = "IOCommand is not serializable"
          "USB Serial Number" = "00000000258233f62023"
          "IOClassNameOverride" = "IOUSBDevice"
        }