Apple's high-priced Mac storage, including the internal SSD, has hidden bottlenecks under certain scenarios.In some cases, a third-party Thunderbolt 4 SSD connected externally performs better than the MacBook Pro's internal SSD, especially for reading.Write performance on the internal SSD drops when the SLC cache is full.It is important to maintain ample free space on the SSD to utilize the SLC write cache fully.