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

Steven M. Bellovin smb at cs.columbia.edu
Tue Dec 12 01:10:23 EST 2017

On 11 Dec 2017, at 23:26, Bill Cole wrote:

> On 10 Dec 2017, at 21:14 (-0500), Steven M. Bellovin wrote:
>> My suspicion is that the problem has to do with very large 
>> directories on APFS file systems
> This would be shocking. One of the rationales for APFS existing is 
> that the HFS foundation was played out for dealing with large 
> directories efficiently. I haven't looked into the details (life is 
> short...) but if APFS is *worse* than HFS{+,X} with large directories 
> then Apple is in a worse state than I had thought...

Yah. I have no other explanation, though. To give a current example, on 
a machine -- an old one, to be sure -- a Time Machine backup started 
almost 10 hours ago. It's dumped 77.5 MB -- out of a total of 152.7 MB 
-- in that time, and it's been at about 77 MB for the last ~7-8 hours. 
At some point, though, it will pass the expensive point and run at a 
reasonable rate. This dump is to a directly connected USB 2.0 drive. And 
the CPU is about 96% idle, according to 'top'.

Btw: by "big", I mean that I have one mailbox with 114K messages; the 
directory itself is 3.6 MB. No other mailbox is more than half that 
size, though I have four that are over 1 MB.

I'm not hearing of problems like mine from anyone else, though. The best 
suggestion thus far is by Patrik, who suggested excluding Messages from 
dumps, but Benny suggests that that's problematic. I may try it for a 
few days just to see if it helps; if it does, it would nail down the 
immediate cause.

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

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