Is my Time Machine drive causing issues?

I have a refurbished early 2015 MBP running High Sierra. I use a Western Digital My Passport external drive as for Time Machine. I usually leave it on, letting it sleep. Twice now in the past several months the machine has gone into the Recovery Mode utilities window while sleeping.

Each time I’ve been able to successfully restart, but only after unplugging the Time Machine drive.

Between these instances, everything works fine and once it restarts, I can reconnect the Time Machine drive.

Any ideas as to what might be happening?

I vaguely recall some Western Digital hard disk drivers causing problems for Apple users a few years ago. Can you try using another drive for Time Machine? (This is a good idea anyway - Time Machine will happily backup to more than one drive and give you some redundancy)

How is the My Passport drive formatted? It should be Mac OS Extended (Journaled) and the Scheme should be GUID Partition Map. Unless the drive came properly formatted for Mac you need to reformat it prior to using it for Time Machine. Reformatting will destroy your data.

Thanks for the feedback. The drive is formatted correctly and I have been using it for several years. It may not be the Time Machine drive – I found a thread on the Apple Community forum that indicated it might be an issue the SSD in the MBP.

Since you mentioned you have been using it for several years I’m wondering if the drive is starting to fail. Why don’t you try another drive and see if you still have the problem.

Definitely worth a shot. I’m curious though, would a failing external drive cause the laptop to boot into recovery mode?

It shouldn’t. But there’s a lot of voodoo involving the macOS boot sequence these days.

You should check the System Startup preferences (System Preferecnces → Startup Disk) and make sure your internal SSD’s boot volume is selected:

Screen Shot 2021-12-28 at 15.27.32

If nothing is selected (or if the wrong device is selected), that could be the cause of your problems.

When a Mac boots up, it tries to boot from the selected Startup Disk. If that disk can’t be found, or if it’s not bootable, then the system will search all available storage volumes and will try to boot the first one that is bootable - which may not be the one you expected.

In this case, it is possible that the Startup Disk preference may be pointing to your Time Machine volume. This is clearly not the correct option, but the boot loader software may respond to this configuration by entering Recovery mode (since that’s where you need to be in order to restore a running system from a Time Machine backup). When the TM disk is not connected, it will search other devices, find your internal SSD, and then boot from it.


Another possibility. According to Apple’s description of the secure-boot process, if the T2 chip’s security process fails to authenticate the OS, your Mac will boot into recovery mode (or a T2-recovery or T2-DFU mode, if the T2 chip itself has a non-recoverable problem).

This supports my previous statement about the Startup Disk having bad data. If it points at a disk volume that appears to be bootable but really isn’t (maybe a TM volume), or if it points to an actual bootable volume that fails the T2 authentication policy (permit external boot device, signature requirements), then you will end up booting into recovery mode.

Similarly, if the Startup Disk preference is not configured at all, then Boot ROM’s search may end up finding something on the TM volume before it finds your internal macOS system, which could end up failing in the same way if what it finds is invalid or fails the T2 security checks.