There are MANY threads about this issue both here and on other sites, including Apple's own support forums. I've been pounding through EVERY possible user-controllable solution offered in ALL threads: cables, powered hubs, power settings, the sudo change to set external drive sleep to the max, etc. Here are my conclusions from much testing:
- Monterey likely has external drive bugs.
- It doesn't matter if you connect via USB-A or USB-C.
- It isn't only about Time Machine drives but ANY drives can do this. The key seems to be connection type, how long a drive is connected and maybe age of enclosure.
- It isn't only about sleep but sleep seems to be the easiest catalyst to make it happen. I've had definitely-awake external drives transferring files to definitely-awake Mac Studio unexpectedly eject during a file transfer... so neither could possibly be asleep.
- It seems to be an issue much more prevalent with HDD-based externals than SSD externals. Single drive HDD boxes seem to work much better than RAID HDDs. RAID SSDs seem to generally "just work."
- Probably has nothing to do with formatting, though I haven’t seen enough of this to feel pretty confident about this one.
- While some think powered hubs make the difference, I have tested through THREE powered hubs by 3 different manufacturers. It appears to resolve the problem for some but not for others. All 3 could not resolve it for me with an external drive also powered.
- the . upgrades to Monterey seem to have each got some declarations of "problem solved" only to have some come back later saying it had returned.
- Some seem to be having better luck with thunderbolt drives using the thunderbolt protocol, so this may be (probably is) more of a USB issue. But again, not only USB-A... USB-C seems- in my experience- to be no better at combating this issue.
- There seems to be an even bigger issue with older RAID HDD boxes, though latest generation boxes from Lacie and OWC have been reported to work by some. I have one purchased new in 2018 that is perfectly functional with 2 Intel-based Macs running macOS < Big Sur but- through the same cable and all else being equal- will not stay connected for longer than a few hours max to a brand new Mac Studio running Monterey (including during cycles where that Studio definitely does not get to sleep because I'm steadily using it during those times)
- While possibly separate from this, I am also noticing an issue with wired Ethernet connections in what I'll call a "blink" of lost connection. Running Dropbox puts the Dropbox icon in the menu bar. When Internet is disconnected, it "grays" out signifying no connection. On the Monterey Studio, it is "blinking" off regularly throughout the day. On wired Intel Macs, it is a much more stable connection. Before Dropbox gets the redirect blame, I opened Airport Utility to simply monitor "blinks" and I see regular "blinks"... especially when UPLOADING files within a local network (to a Synology NAS for example). These are brief (a few seconds) but feel like the Ethernet connection "crashes" and then "boots up" again over and over throughout the day. Is there some relationship between ALL ports (USB, Thunderbolt and Ethernet)... perhaps some kind of central controller that might share a bug(s)? If so, and USB jacks are also "blinking," would that explain the "unexpected ejections"? Counter to this gut feel, single drive HDDs and most SSDs seem to be long-term stable. In another thread, a user seemed to have found a partial solution to this (ethernet "blink") problem by unchecking one box in the Network connections "advanced" options, which did significantly reduce downloading "blinks" but doesn't seem to do anything for uploading "blinks."
Bottom line: Having tried EVERYTHING a user can, I'm mostly convinced there
IS a bug(s) in Monterey. Apple fans are quick to redirect blame to anything & everything else (firmware, cables, third party hardware, hubs, etc) but anyone with an Intel Mac running macOS < Big Sur is likely to find that a problematic drive works FINE when reconnected to Intel Macs running pre-Big Sur macOS. Hook the same through the
same cable to a Monterey Mac and you'll have a fair chance of "unexpected ejections." Remove any middleman options like hub for a direct connection and you are likely to STILL see the problem, which can then be immediately resolved by direct connect to Intel Macs running macOS BEFORE Big Sur or Windows in bootcamp.
There are also a good number of reports of Intel Macs working fine BEFORE upgrading to Big Sur or Monterey and then this happening to Intel Macs too
after upgrading. For me, this one thing implies it's probably not Mac hardware but Big Sur/Monterey software.
Resolution: from countless interactions with many people, the resolution until hopefully Apple gets around to debugging this part of macOS seems to be to try new enclosures. Some enclosures work and others don't. Apparently U in USB means something different than intended right now. If you go this way, buy from someone with a good return policy. Basically, we are all guinea pigs with USB.
I have (hopefully temporarily) given up on a 2018 OWC RAID HDD box but a single HDD in
OWC Mini Stack STX has been stably connected for a few weeks. Another user picked up the
latest OWC RAID HDD box and claims it is remaining stably connected to their Studio. Another user claims the current generation Lacie 2big Dock Thunderbolt 3 RAID HDDs remain consistently connected. Anyone working with SSDs seem to generally not have this problem, including RAID SSD boxes. Thunderbolt connections seem more stable than USB (which is what I've switched to myself in the link to that Mini Stack). Short connects & then manual ejects generally won't show this issue: it's LEAVING IT CONNECTED for at least several hours- especially through a Mac sleep cycle where one is most likely to experience this. However, it can be as fast as only minutes too.
In short: very new hardware seems more likely to work than even stuff only a few years old. But the game to be played is not what U in USB stands for... more "hit or miss" lottery where something you buy new MIGHT work. Good luck to all and I hope this post helps you.