If your Mac shows errors like “Invalid node structure”, “Keys out of order”, or “Invalid sibling link”, your HFS+ catalog directory (the on-disk index of every file and folder) is likely damaged. Disk Drill can often fix this by rebuilding the catalog with its HFS+ Rebuild Directory method. Preview the reconstructed folder tree, then either write the new directory to the disk or mount the found items as a virtual disk to recover your data safely.
What is the HFS+ Catalog Directory (Catalog File)?
It’s the master index of an HFS+ volume. HFS+ stores this index as a B-tree (a balanced tree) inside a special on-disk Catalog File. That B-tree contains a record for every file and folder, keyed by the parent folder’s ID and the item’s name. The catalog is one of several “special files” that make an HFS+ volume work (others include the Extents Overflow, Allocation, Attributes, and Startup files).
How Does the HFS+ Catalog Get Corrupted?
Common real-world causes include:
- Unclean shutdowns or unsafe removal (power loss, kernel panic, yanked cable) that interrupt metadata writes-even on journaled volumes.
- Failing media or bad blocks, which physically damage B-tree nodes.
- Disk full events during repairs or heavy metadata churn (catalog rebuilds can fail with “CreateNewBTree returned -34 Disk full error“).
- Driver/firmware glitches or prolonged fragmentation affecting catalog nodes.
Typical symptoms and error messages. When Disk Utility / fsck_hfs checks an HFS+ volume, you might see:
- Invalid node structure, Invalid record count, Invalid B-tree node size
- Invalid sibling link, Keys out of order
- “The volume could not be repaired” (exit code 8), sometimes followed by (-69845) in Disk Utility logs
These are all consistent with catalog B‑tree damage.
Before You Rebuild: Do This First (Best-practice Checklist)
- Stop writing to the affected disk/volume.
- Create a Byte-to-Byte backup (sector-level image) of the whole device to another healthy drive. Disk Drill includes a free Byte-to-Byte Backup tool; scan the image, not the failing disk.
- If the drive shows I/O errors or disconnects, prioritize imaging over any repair attempt; repeated writes can make things worse.
Disk Drill`s Unique HFS+ Rebuild Directory (Catalog) Method
When Disk Drill detects lightweight directory damage on an HFS+ volume, it exposes a purpose-built workflow:
- Look for the Rebuild button. In eligible cases, Disk Drill shows “Rebuild HFS+ catalog file” when you right‑click the corresponding HFS+ partition.
- Click “Rebuild HFS+ catalog file”. Disk Drill reads the partition/boot sector and uses that metadata to locate the HFS+ catalog’s B-tree, then reconstructs the directory.
- Preview the result. You’ll see a virtual file tree representing the rebuilt catalog. Verify the folder structure and key files.
- Choose how to proceed:
- Rebuild — write the new catalog back to the original volume (fastest way to make the disk mountable again).
⚠️ Warning: This operation is irreversible. It will overwrite the volume’s file system metadata on your drive. We advise to create a verified backup or a byte‑to‑byte disk image before proceeding.
- Mount data as a disk — mount the rebuilt tree to a virtual disk and copy data out (safest if you want to avoid any writes to the problem drive).
- Or go Back to try other recovery methods.
- Rebuild — write the new catalog back to the original volume (fastest way to make the disk mountable again).
Good to Know (and Limits)
- Rebuilding the catalog changes metadata structures, not your file contents. If the media is failing, write‑backs may still be risky—prefer imaging and Mount data as a disk when in doubt.
- Many modern Macs default to APFS, but external disks and older Time Machine sets may still be HFS+, so these instructions remain relevant. (Time Machine now prefers APFS but still supports Mac OS Extended.)