Hey @wolfie42 –
Right now, Local the application has to be on the primary hard-drive. You can move the site files to the secondary drive. The default location for new sites is set in “Preferences > New Site Defaults > Sites Path”
There will be some improvement on these sorts of things in the future with the release of https://localbyflywheel.com/community/t/lightning-fast/12609 , so be on the lookout for that release!