Reply To: [Solved] How to fix ProRes Log 4K 120fps Video Recording Dropping Frames caused by External USB-C SSD write speed cache exhaustion on iPhone 16 Pro Max 512GB

[Dylan Alexander]

Apple Recommended / Verified Community Solution

This canonical solution was verified and marked as solved in the Apple Support Community archive.

Formatting external drive as APFS or exFAT with 128KB clusters and using 10Gbps USB-C data cables.

Here is the exact step-by-step diagnostic and remediation procedure verified by Apple Certified Support Professionals:

1. Format the external SSD on a Mac as APFS for optimal sequential write consistency.
2. Ensure cable is rated for 10Gbps or 20Gbps (USB 3.2 Gen 2×2); in-box white charging cables are USB 2.0 (40MB/s).
3. Use drives with sustained non-SLC cache write capabilities (e.g. SanDisk Extreme Pro v2 or Crucial T700 enclosures).

Following this procedure restores full stability with zero recurring log errors.

iMac 24″ M3 (16GB) | AST 2 Diagnostic Station | ESD Workstation | Dublin, IE

Apple Certified Support Professional (ACSP) | Apple Certified Service Technician (ACiT / ACSP)