Would I notice a significant loss in performance should my project files be saved on a different internal drive to the editor? e.g, UnityEditor on C:, Unity project files + assets on D:
Would I notice an even greater loss should those project files be saved on an separate internal HDD over a separate SSD?
An extension to this question being, project files saved on an external hard drive? Will I experience even greater loss in performance/waiting around compared to an internal save.
Only if Unity frequently accesses its own files on disk at the same time it is accessing your project files, where access to your project is waiting for access to the editor’s files to complete. I doubt this is the case.
I guarantee any project on an HDD will have inferior performance to the same project on an SSD. Unity projects include large numbers of small files, which are a nightmare for HDD’s.
External vs internal storage performance depends entirely on how the two are connected. The performance of the interface, and any external controller involved. For example, if you had two identical SATA drives, one connected internally, and one connected externally via eSATA, you’d very likely see identical performance between the two, as the interface performance is virtually identical. You though have internally a PCIe NVME internal SSD, and an external SATA SSD in a USB drive enclosure connected to an old USB 2.0 port, you will see exponentially better performance on the internal drive, all because the chosen interfaces have vastly different speeds.
Thank you for such a comprehensive answer. I think I’ll go ahead with putting my projects on a separate internal SSD to the editor, it’s just nice for keeping my drives and folders tidy.