Forcing a Windows 10 upgrade in an iSCSI environment

If you boot Windows machines from iSCSI, you should know that the Windows 10 Upgrade doesn't load iSCSI drivers and dumps you into a recovery environment. However, there is a way to get around that.

Once the Windows 10 recovery environment (Windows PE) boots, use the Advanced Options to obtain a command line.

To start the iSCSI initiator:

wpeutil initializenetwork
net start msiscsi
iscsicli qaddtargetportal portal.ip.address.here
iscsicli listtargets
iscsicli qlogintarget iqn.xxx.xxx
iscsicli PersistentLoginTarget T * * * * * * * * * * * * * * * 0 (that was fifteen * characters)
iscsicli ListPersistentTargets
iscsicli ReportTargetMappings

Once this is ready, you can manually install Windows 10:

 c:\$Windows.~WS\Sources\Windows\sources\setuperror.exe

For reference, here are the hidden upgrade folders and their meanings:
"Windows.WS = Windows Server Folder"
"Windows.BT = Windows Backup Files"
"Windows.Old = Windows backup files"

Have fun!