Apple's macOS Tahoe 26.3 update released on February 11 is causing external drive mounting problems for some Mac users. The update, which promised machine learning performance improvements for M5 users, appears to have introduced an undocumented change affecting external storage devices.

Affected users report drives failing to mount properly or experiencing drastically reduced read/write speeds. AppleInsider staff have encountered similar issues, particularly with SSDs. Some users see speeds drop to just a few megabytes per second, while others face complete mounting failures. One user documented their Samsung T7 SSD displaying error messages, with the drive containing their only copies of video files.

This isn't Apple's first external drive issue in macOS 26. Similar problems appeared during early developer betas but seemed resolved until resurfacing in recent updates. Apple's macOS Tahoe 26.4 developer beta release notes mention two external drive-related known issues, including HFS media failing to mount automatically. The current 26.3 problems appear broader, affecting APFS-formatted drives as well. With relatively few public complaints, the issue seems limited to specific configurations, though the exact affected hardware remains unclear.