Time Machine drive takes long time (~5 minutes) to mount on boot

Question

My time machine backup drive (a Samsung T5, 1TB) is giving me trouble: I noticed that it takes a long time for the drive to show up on my desktop (5 minutes or so) after start or restart. The drive indicator light flashes a lot, showing some kind of activity, but I don’t know what. I checked that it is not doing a fsck. Even stranger is the fact that the drive shows up right away when I plug it in after the boot has completed and I see a normal desktop. Other USB sticks mount and unmount just fine. The troublesome drive shows up right away on a different, much older Mac. The lsof command returns nothing when I try

sudo lsof +D /Volumes/Samsung_T5

The Samsung SSD app, called SamsungPortableSSD.app, shows the drive as disconnected during the slow mount from boot. Disk Utility shows no errors (sudo time diskutil verifyVolume disk2s2). The drive already has about 750GB of backups on it.

Is there some logging facility I can turn on or browse to see what’s going on during the 5 minutes the drive is flashing without mounting? Is it worth it to try USB logging? What are the risks?

In the meantime, I can browse through the backup files on the Time Machine external drive through the Finder just fine. I would like to be able to preserve all these backups and fix the problem. Is this possible? Or do I really have to erase it all, format, and start over? Or is there an intermediate path where I can preserve maybe five total checkpoints over two years' worth and the rest gets erased? In the end I’d like to get back to normal behavior where the drive shows up right away on start and goes away quickly on shutdown.

Machine: I’m running Big Sur 11.2 on a 12-inch, Early 2015 Retina MacBook.

History:

Initially the drive worked fine for two years even though I didn’t install the driver. The trouble started about two months ago or so during Catalina and got worse with the Big Sur versions. The problem first became visible when the drive didn’t show up right away after boot. Later on, the actual shutdown would take a long time, again maybe five minutes or so. It really got my attention when I got a black screen of death after a long shutdown with an accompanying kernel panic report. Things are much better since I’ve installed the driver: now the drive will always eventually mount after boot (as opposed to almost never) and there are so far no more black screens of death. I can accept slow mount and unmount times, but I'm really concerned about the kernel panics. What risk is there now of kernel panics with an updated driver?

Answer 1

On macOS you don’t need to install any drivers for external drives that comply with the USB Mass Storage class, which the Samsung does (unless you’re doing something funny like using their proprietary encryption scheme). Any external USB SSD will ‘just work’ when you plug it in. I would uninstall the driver as it can do more harm than good, particularly with the major rewrites to the driver architecture in Catalina and Big Sur which not all third-party developers have caught up with yet.

You’re definitely right to worry about the slow mounts on boot, though. That can be due to a variety of things. One of these is a heavily worn SSD, which could be the case if you’re using it for Time Machine, but two years isn’t a very long time. It may still be valuable for you to run the Smartmontools package (which will also require you to install USB SMART support) in order to determine the wear & lifespan on your SSD. Heavily worn SSDs will have increased latencies which get worse over time. If you’re only seeing this issue on first mount and you’re not seeing a reduction in read or write speed, though, then that’s unlikely to be the issue.

It sounds like you’re more concerned with your kernel panics. Without seeing the panic reports, we can’t determine if they’re something you should worry about or if they’re even related to your SSD. Can you please provide your panic logs? They’ll be found in /Library/Logs/DiagnosticReports and have the file extension .panic. Put those up on PasteBin and we can review them.

To your question of preserving your backups: I don’t know of a straightforward way to cherry-pick specific checkpoints (although there may exist tools out there that I just haven’t looked for, so feel free to DuckDuckGo it). Time Machine is persnickety about the contents of its backup bundle and any omissions could result in an unreadable backup. I would instead try cloning your entire SSD to another drive wholesale and pointing TM to that. (But I have never done this and it’s entirely possible that TM will detect the different device UUID and force you to recreate the backup anyway.) You have to be ready to accept that you might need to start from scratch.