Context
You may see a red bar under your shared drive connections, which may also say "367 GB free of 5.99 TB".
Details
If you see this message, your drive is not running out of space. The data on these drives is cache-only. The drive will fill with cached copies of recently accessed data, but simultaneously remove the oldest cached items. Because of this, the drives will not run out of space while still maintaining access to your data stored within.