Bug in Apple's fsck_hfs on macOS Sequoia Falsely Reports Corruption on Large HFS+ Volumes
By
Kivanc G
Front-window bakery material. Catches the eye, delivers the goods.
Summary
A detailed technical investigation into a bug in Apple's fsck_hfs tool on macOS Sequoia. The tool falsely reports corruption on large HFS+ volumes (24TB+) on machines with 8GB RAM due to a cache exhaustion issue in the extended attributes check. The author walks through their debugging process, including analyzing on-disk structures, tracing system calls, and ultimately identifying the root cause as a memory allocation failure in the B-tree cache. The data itself is not corrupted—only the diagnostic tool is flawed. Machines with 16GB+ RAM are unaffected.
Key quotes
· 3 pulledYour data is fine — the bug is in the tool, not the filesystem.
fsck_hfs in macOS Sequoia (version hfs-683.x) has a cache exhaustion bug that reports false corruption on large HFS+ volumes.
On machines with 8 GB RAM, volumes of 24 TB or larger trigger 'Couldn't read node' errors during the extended attributes check.
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