[MlMt] High Sierra, APFS, Time Machine, and MailMate...

[Steven M. Bellovin]

Seems like an improbable subject line--but is anyone else who uses 
MailMate on High Sierra/APFS suddenly having serious Time Machine 
performance issues? I am, on two different laptops. An iMac, which has a 
hard drive and hence HFS+, is not having any trouble.

The overall symptom is that backups take *many hours*, with sudden, 
inexplicable stalls. I say "inexplicable" because Activity Monitor shows 
essentially no CPU, network, or disk activity -- but the backup just 
*stops*. I normally don't run MailMate on one of the laptops; its 
backups complete in a rational amount of time. When I do, it sees the 
same stalls. In fact, I'm running MailMate on it right now so that I can 
see what happens on my primary laptop when I exit MailMate. Sure enough, 
that machine is now behaving.

My suspicion is that the problem has to do with very large directories 
on APFS file systems, but I don't know that for sure. I have some very 
large mailboxes, though, and these are of course active when MailMate is 
running.  And of course, that doesn't explain why I don't see any system 
activity.

Is anyone else seeing this? Does anyone have any work-arounds, other 
than "don't have such large mailboxes" or "don't run APFS"? I do have a 
new laptop on order; I'm seriously tempted to reformat it as HFS+ before 
I start using it.


         --Steve Bellovin, https://www.cs.columbia.edu/~smb