HFS+ Legacy and Migration

While APFS is now the default, HFS+ (Mac OS Extended) served macOS for nearly two decades and remains relevant. You’ll encounter it on older systems, external drives, Time Machine backups from before 2017, and in specific scenarios where APFS isn’t appropriate.

HFS+ History and Design

HFS+ debuted in 1998 as an evolution of the original Hierarchical File System (HFS) from 1985. Key improvements included:

• 32-bit allocation blocks: vs HFS’s 16-bit, allowing efficient use of large volumes
• Unicode filenames: Up to 255 UTF-16 characters
• Journaling: Added in Mac OS X 10.2.2 (2002) for crash recovery
• Case sensitivity option: Added for Unix compatibility

HFS+ Variants

HFS+ comes in several flavors, identified in diskutil:

# Identify HFS+ volumes
$ diskutil list
...
   2:                  Apple_HFS Backup                   1.0 TB     disk2s2
...

$ diskutil info disk2s2 | grep "Type"
   Type (Bundle):                  hfs
   File System Personality:        Mac OS Extended (Journaled)

Why HFS+ Still Exists

Compatibility Scenarios

Older Mac hardware: Macs that can’t run macOS High Sierra or later require HFS+.

Bootable external drives for old Macs: If you need a bootable drive for older hardware.

Windows cross-compatibility: Some tools read HFS+ but not APFS. (Note: Neither is truly cross-platform without third-party tools.)

Specific applications: Some virtualization or disk imaging tools may expect HFS+.

Time Machine Archives

Time Machine backups created before APFS store data on HFS+:

# Check Time Machine drive format
$ diskutil info /Volumes/TimeMachine | grep "File System"
   File System Personality:        Mac OS Extended (Journaled)

Modern Time Machine on APFS uses snapshots differently than the hardlink-based approach on HFS+.

HFS+ Features

Journaling

The journal records filesystem changes before they occur, enabling recovery after crashes:

# Check journaling status
$ diskutil info disk2s2 | grep -i journal
   File System Personality:        Mac OS Extended (Journaled)
   Journal:                        Journal size 40960 KB at offset 0x...

# Enable journaling
$ sudo diskutil enableJournal disk2s2

# Disable journaling (not recommended)
$ sudo diskutil disableJournal disk2s2

Transparent Compression

HFS+ supports transparent file compression (introduced in Snow Leopard):

# Check if a file is compressed
$ ls -lO /bin/ls
-rwxr-xr-x  1 root  wheel  compressed  38704 Jan  1  2020 /bin/ls

# The compressed flag indicates HFS+ compression
# Actual on-disk size may be smaller than reported size

# Get actual disk usage
$ stat -f "%z bytes (logical), %b blocks (physical)" /bin/ls

Note: While APFS carries forward compressed files, it doesn’t actively compress new files.

Resource Forks and Extended Attributes

HFS+ natively supports Apple’s extended file metadata:

# View resource fork (if present)
$ ls -l /path/to/file/..namedfork/rsrc

# View extended attributes
$ xattr -l file

Working with HFS+ Volumes

Creating HFS+ Volumes

# Format as HFS+ (Journaled)
$ sudo diskutil eraseDisk JHFS+ "BackupDrive" GPT disk2

# Format a single partition
$ sudo diskutil eraseVolume JHFS+ "NewVolume" disk2s2

# Create case-sensitive HFS+
$ sudo diskutil eraseDisk JHFS+X "CaseSensitive" GPT disk2

Verifying and Repairing

# Verify HFS+ volume
$ sudo diskutil verifyVolume disk2s2
Started file system verification on disk2s2 Backup
Checking Journaled HFS Plus volume
...
The volume Backup appears to be OK
Finished file system verification on disk2s2 Backup

# Repair HFS+ volume
$ sudo diskutil repairVolume disk2s2

# For more serious issues, use fsck_hfs directly
$ sudo fsck_hfs -fy /dev/disk2s2

Command-Line Formatting with newfs_hfs

For more control, use the underlying filesystem tools:

# Create HFS+ filesystem with specific options
$ sudo newfs_hfs -v "MyVolume" -J /dev/disk2s2

# Options:
#   -v: Volume name
#   -J: Enable journaling
#   -s: Case-sensitive
#   -b: Block size

Converting HFS+ to APFS

In-Place Conversion

Apple provides non-destructive HFS+ to APFS conversion:

# Check if conversion is possible
$ diskutil info disk2s2 | grep -i "APFS"

# Convert (non-destructive, but backup first!)
$ sudo diskutil apfs convert disk2s2
Converting HFS volume to APFS...
...

Conversion requirements:

• macOS High Sierra or later
• Journaled HFS+ (not plain HFS+)
• No Fusion Drive issues
• Sufficient free space for conversion process

When Conversion Isn’t Possible

If conversion fails or isn’t desired:

# Backup, erase, restore approach
# 1. Backup all data
# 2. Erase as APFS
$ sudo diskutil eraseDisk APFS "NewDrive" GPT disk2
# 3. Restore data

HFS+ Limitations

No Space Sharing

HFS+ requires fixed partition sizes:

# Partition must be resized explicitly
$ sudo diskutil resizeVolume disk2s2 500GB

No Native Snapshots

HFS+ lacks APFS’s snapshot capability. Time Machine on HFS+ uses hard links to directories, a workaround with its own complexities.

Performance on SSD

HFS+ wasn’t designed for flash storage:

• No TRIM support optimization
• Journaling patterns not ideal for SSD
• File operations less efficient than APFS

File Size and Volume Limits

Practical limits are lower due to macOS constraints.

Interacting with HFS+ from Unix Perspective

Mount Options

Hbash

View mount options for HFS+ volume

$ mount | grep hfs /dev/disk2s2 on /Volumes/Backup (hfs, local, nodev, nosuid, journaled)

Mount HFS+ volume read-only

$ sudo mount -t hfs -o ro /dev/disk2s2 /Volumes/Backup

### File System Attributes

```bash
# Get HFS+ specific information
$ /usr/sbin/fstyp /dev/disk2s2
hfs

# Detailed filesystem info
$ sudo diskutil info -plist disk2s2 | plutil -p -

Common Issues

Catalog File Corruption

HFS+’s B-tree catalog can become corrupted:

# Symptoms: Files disappear, disk errors
# Solution: Run Disk Utility or fsck_hfs
$ sudo fsck_hfs -fy /dev/disk2s2

Journal Overflow

On heavily used volumes, the journal can overflow:

# Symptoms: Slow performance, errors
# Solution: Recreate journal
$ sudo diskutil disableJournal disk2s2
$ sudo diskutil enableJournal disk2s2

Permissions Repair (Deprecated)

Older macOS versions had “Repair Disk Permissions.” This is no longer relevant on modern macOS where system files are protected by SIP.

When to Use HFS+ Today

Recommended for:

• External drives shared with older Macs
• Time Machine destinations for older Mac backups
• Virtual machine disk images (check VM software requirements)
• Bootable drives for pre-High Sierra Macs

Not recommended for:

• Primary macOS boot drives (use APFS)
• General storage on modern Macs
• SSD drives (APFS is better optimized)

Summary

HFS+ served macOS well for nearly 20 years, but APFS represents the future. Understanding HFS+ remains valuable for:

• Working with legacy systems and backups
• Troubleshooting older storage media
• Understanding the evolution of macOS storage
• Specific compatibility requirements

For new storage, prefer APFS unless you have a specific reason to use HFS+. The performance, reliability, and features of APFS make it the clear choice for modern Mac use.