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

Steven M. Bellovin smb at cs.columbia.edu
Mon Dec 11 10:45:55 EST 2017

On 11 Dec 2017, at 10:00, Paul Sture wrote:

> On 11 Dec 2017, at 3:14, Steven M. Bellovin wrote:
>> 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.
> I saw something similar last week when I wiped my TM disk and started 
> afresh. TM got to 120GB out of 750GB and then showed little progress 
> for several hours.
> I resolved it by quitting various apps.  I cannot recall which one I 
> quit that got TM working again, but I have quite a few that clock up 
> CPU and I/O even when not in focus.
If it were only once, I wouldn't worry, but I see it every time I do a 
backup if MailMate had been running.

> The following StackExchange article may shed some light.
> https://apple.stackexchange.com/questions/212537/time-machine-ridiculously-slow-after-el-capitan-upgrade
> Scroll down to the first answer for details.

I'm not seeing any "throttled" entries. I'll try disabling throttling, 
but if memory serves I've already tried that unsuccessfully.

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