I was migrating files from an old Mac running Mojave to a new one running Monterey, using an external SSD formatted with APFS (encrypted), and noticed that there was some data being lost. I had created a .rtf file to note the files I'd copied, and copied that onto the external SSD too. It showed as being on the external drive in Finder, but when I ejected the drive and plugged it into the new Mac, that file was missing. I repeated the process again, recopying the file from the old Mac onto the external drive, then copied some more files, and then edited the .rtf file. When I ejected the drive and plugged it into the new Mac, the .rtf file was there this time, but the latest edits where missing! Yes, I am ejecting the drive correctly using Finder, and not simply unplugging it.

Has anyone had similar problems, and found a solution?

I assume it is caused by macOS not flushing file buffers when you eject the external drive. I've never noticed this problem before, but in the past have always used spinning disk external drives, and never formatted with APFS. So I don't know if it is related specifically to APFS, or specifically to Mojave or Monterey.

  • 2
    It feels like there'd have been a big hue and cry if this had been widespread. Maybe it's some kind of peculiar interaction with that particular model of drive? How are you attaching that drive? I've seen lots of buggy USB SATA adapter chips.
    – Spiff
    Aug 22, 2022 at 3:45
  • Update. I moved some more files, but this time reformatted the drive with ExFAT instead of APFS, but had the same problem. It seems like the last file added fails to flush to the drive. As far as I can tell, all the other files seem to copy correctly. I "solved" my problem by copying an extra file that I don't actually want on the drive, after I've copied all the files I do want. However, it's very disconcerting. Aug 23, 2022 at 10:21
  • @Spiff Yes, you'd think so, and I do recall someone else mentioning it, but can't recall where I saw it. The drive is actually the original 500GB SSD from a 2015 Retina MBP, that I'd upgraded to a 1TB drive. I put the 500GB drive into an external enclosure. Yep, it's 7 years old, so perhaps that is the issue, but it's not like there's random data loss, it appears to always be the very last file added that doesn't get flushed to the drive when ejected. Aug 23, 2022 at 10:25
  • @Spiff I am copying data from that same 2015 rMBP, and it plugs directly in via the USB cable that came with the enclosure (which is from OWC, seems to be high quality, and is around 3 years old, but rarely used). I am then plugging it into my new 2021 M1P MBP using the same cable and a cheap USB to USB-C adapter. Since the data loss appears to always be the last file copied, I find it hard to believe that the problem is due to the adaptor or enclosure. Maybe the drive itself isn't flushing correctly. Or possibly one of the long list of weird bugs in macOS these days. Aug 23, 2022 at 10:29


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.