This is because the pool created by Stablebit DrivePool is a virtual logical volume. All read and write requests to this pool are first received and processed by DrivePool itself, which then distributes them directly to the underlying physical drives. Since these I/O requests do not pass through the storage layer where PrimoCache operates, configuring a cache task for the virtual pool cannot produce any acceleration.
Workaround:
Add the individual physical drives that make up the pool directly to a PrimoCache cache task. This way, when DrivePool sends read/write requests to the underlying physical drives, they can be processed and accelerated by PrimoCache.