Hi there,
WDS requires a boot image and a boot image can only link to 1 deployment share. For every deployment share, a different boot folder/file will be created.
Simply remove the DeployRoot line from the bootstrap.ini file of each of your deployment shares, and then update your deployment shares to regenerate the boot images. Now, when a target computer is started from a boot image, a dialog will be displayed asking you to type the UNC path to the deployment share you want to use.
Dual Deployment Shares in MDT 2013 https://social.technet.microsoft.com/Forums/ie/en-US/81ae186c-437b-4721-a7f0-4de5e8447cc6/dual-deployment-shares-in-mdt-2013?forum=mdt
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