I updated my new 16″ MacBook Pro with the M5 Max chip to Mac OS 27 and then Mac OS 27.0.1.
The computer started acting funny when I restarted the MacBook Pro, and I typed my password, watched the progress bar creep forward a sliver, and then nothing. It sat there. I restarted and got the same result.
If you’re a photographer with a pile of external drives, this one might save you a day.
What I tried first
I did what most people would do and worked down the list:
- Force shutdowns and restarts. Same hang.
- Safe Mode. It didn’t get me in while my externals were connected.
- First Aid in Disk Utility on every volume. Clean.
- Reinstalling macOS over the top. Same spot.
The clue came when I unplugged everything. With no external devices attached, the Mac booted normally. So the Mac was fine, and something I had plugged into it was the problem.
Chasing the wrong suspects
My setup runs through a Wavlink hub for Ethernet and external drives, so I made the hub my first suspect. I updated its drivers. It still hung.
Next I looked at my Samsung T7 SSDs. Samsung offers firmware updates for the T7 through its free Samsung Magician software, so I updated those too. It still hung.
The accidental breakthrough
Frustrated, I started pressing the power button over and over. Somewhere around the ninth try, the Mac got past the login hang and started up.
That’s not a fix, but it was a clue. I described everything to Claude, and it asked a question I hadn’t thought about: what format are your SSDs?
My answer was Mac OS Extended (Journaled), also called HFS+. It’s the old Mac format. I’d been using it for years because it always worked.
The suggestion was to convert the drives to APFS, Apple’s modern file system. Apple has been phasing out HFS+ (Mac OS Extended, Journaled) support for a while. Legacy HFS+ volumes can stall at login while the system tries to mount or index them, especially on a new major release. Converting to APFS gives macOS a filesystem it handles natively and quickly.
After I converted them, the hang stopped.
How to convert without erasing anything
You don’t have to reformat. Apple lets you convert a Mac OS Extended volume to APFS in place, and your files stay on the drive.
Before you start:
- Back up anything irreplaceable. Conversions are reliable, but you can’t undo one, and an interruption could cost you data.
- Convert SSDs only. Leave spinning hard drives as-is, because APFS is designed for flash storage.
- Don’t convert a drive holding an existing Time Machine backup. Start a fresh backup volume instead.
- APFS drives won’t mount on very old Macs (macOS 10.12 or earlier). If you share drives with one, think twice.
The steps:
- Plug in the drive and open Disk Utility (Applications > Utilities).
- Choose View > Show All Devices.
- Select the drive’s volume in the sidebar, then choose Edit > Convert to APFS. You can also Control-click the volume and pick Convert to APFS. The partition map should say GUID Partition Map.
- Confirm and wait. Don’t unplug the drive during conversion. It’s usually quick, though bigger drives take longer.
- When it finishes, check that Disk Utility lists the format as APFS, then run First Aid once.
- Open your photo library or catalog and make sure everything loads normally.
If “Convert to APFS” is greyed out, the volume probably isn’t Mac OS Extended, or you’ve selected the wrong item. Make sure you’ve selected the volume, not the parent disk, and that Show All Devices is on.
Terminal option: Run diskutil list to find the volume identifier, then diskutil apfs convert diskXsY, replacing diskXsY with your volume’s identifier. Double-check the identifier before you press Return.
What I think happened
I can’t say with certainty why the legacy format caused the hang. My theory is that the Mac was stalling at login while trying to mount and index the older HFS+ volumes on a brand-new machine and OS release. I haven’t confirmed that, and I haven’t proven that the hub drivers and firmware updates played no role. All I can say is that after converting, the problem went away.
The takeaway
When a Mac hangs at login, unplug everything first. If it boots clean, plug devices back in one at a time. And if your SSDs are still on a format from years ago, check it. A few clicks fixed what hours of troubleshooting and a new set of drivers didn’t.
