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I was wondering if anyone had seen errors like the following.

I’m on Big Sur 11.1, Time Machine to a Synology NAS which was started after the upgrade (so it should definitely be APFS). I’ve been running H Oakley's T2M2 utility to scan the Time Machine logs.

Note that these errors do not show up in the System Preferences Time Machine prefpane (so perhaps there's really nothing to worry about).

The “Check Speed” button on T2M2 shows this error:

2021-01-02 08:42:59.840240+0000 Failed to remove directory ‘/Volumes/Backups of random/2020-12-26-181559.previous/Macintosh HD – Data/Users/jaffe/Library/Group Containers/3DZ6694B2C.group.udoncode.copied/assets’, error: 66

The “Check Time Machine” button on T2M2 shows multiple errors like this (note that this does include the specific backup from the single previous error, but also many others — and also note the weird spelling of “writErr”!):

2021-01-02 08:41:39.671012+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-17-144850.interrupted
2021-01-02 08:41:43.009394+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-30-065952.interrupted
2021-01-02 08:41:44.140141+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-15-110003.previous
2021-01-02 08:41:47.864503+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-15-182101.previous
2021-01-02 08:41:49.294281+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-16-125004.previous
2021-01-02 08:41:52.259055+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-18-164158.previous
2021-01-02 08:42:05.478032+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-15-205138.interrupted
2021-01-02 08:42:12.912637+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-29-013753.interrupted
2021-01-02 08:42:15.733565+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-30-030848.interrupted
2021-01-02 08:42:36.242113+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-14-165419.previous
2021-01-02 08:42:37.297566+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-16-093247.previous
2021-01-02 08:42:38.930347+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-16-134505.previous
2021-01-02 08:42:41.419842+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-17-133510.previous
2021-01-02 08:42:42.826467+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-21-133545.previous
2021-01-02 08:42:51.516460+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-15-050915.interrupted
2021-01-02 08:42:52.992397+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-16-202236.interrupted
2021-01-02 08:42:55.150883+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-16-163502.previous
2021-01-02 08:42:58.500571+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-18-172907.interrupted
2021-01-02 08:42:59.840623+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-26-181559.previous
2021-01-02 08:43:01.623108+0000 Error: Error Domain=NSOSStatusErrorDomain Code=-20 "writErr: I/O System Errors" deleting backup: /Volumes/Backups of random/2020-12-20-125724.interrupted

These latter seem to correlate with a set of messages in the "APFS" tab of T2M2:

2021-01-02 10:32:21.585812+0000 Found incomplete backups ready for deletion: (
    "<APFSBackup: 0x7f9bdc69ec80> (2020-12-30-065952.interrupted) trashed",
    "<APFSBackup: 0x7f9bdc608a30> (2020-12-17-144850.interrupted) trashed",
    ... [removed for brevity] ...
)

(I don’t think these two sets of errors are directly related, although they might both be symptoms of the same underlying issue.)

Anyone seen anything like this? Perhaps relatedly, I've had longstanding issues with very slow NAS backups over wifi, although these errors are very recent.

3
  • How did you setup TM on the Synology, did you use the functionality available in the DSM? – nohillside Jan 2 at 14:43
  • Yes, SMB and Bonjour, with some fiddling as I’ve been trying to diagnose speed issues for a while. I should point out that I’ve had this setup for a while but these errors just started a couple of days ago. – Andrew Jaffe Jan 2 at 14:52
  • I've set Bonjour discovery to AFP (don't ask me why), seems to work. Did you check your NAS for disk failures? – nohillside Jan 2 at 15:09

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