How to monitor IO per APFS volume?

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How to monitor IO per APFS volume?

I'd like to be able to monitor the disk IO (read MB/s, write MB/s, IOPS, etc...) per APFS volume. The Activity Monitor seems to show only aggregate IO and not per volume IO. iostat via Terminal seems to show no activity at all for the physical disk assigned to the APFS volume. I did find a version of nmon that was ported to MacOS, but it also shows aggregate disk IO just like Activity Monitor.

Anything I'm missing? Is there a way to monitor IO per APFS volume?

Thanks!

MacBook Pro (2020 and later)

Posted on Mar 30, 2022 6:34 AM

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Answer 1

Joo Chung Author

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Mar 30, 2022 10:20 AM in response to etresoft

Looks like it was user error. I thought just running iostat -d -w5 would show all the disks. But it didn't show the disk for my external raid array. I was wrong about which disk was assigned to the APFS container. It was disk6 and not disk5. And iostat only showed up to disk5 if I didn't explicitly specify disk6.

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Answer 2

etresoft

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Mar 30, 2022 9:09 AM in response to Joo Chung

What are the characteristics of your system and this disk? It seems to work fine on my boot drive.

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Answer 3

Joo Chung Author

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Mar 30, 2022 7:10 AM in response to etresoft

Right. The physical disk associated with my APFS volume is disk5. I start a large copy on my APFS volume and then run iostat -d -w 5 in terminal. iostat shows absolutely no IO on disk5. But clearly it is copying the files as I can see the disk usage increase with 'df -g' and there activity monitor is showing aggregate disk IO.

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Answer 4

etresoft

Level 9

56,728 points

Mar 30, 2022 7:02 AM in response to Joo Chung

Can you show what you are trying in Terminal with iostat? On my machine, iostat shows only information about the physical disk. It refuses to show anything about APFS volumes.

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Answer 5

Joo Chung Author

Level 1

14 points

Mar 30, 2022 10:15 AM in response to etresoft

External TB RAID6 (8 drives) array. Single partition. Single APFS Container. Single APFS Volume. Attached to a MacMini8,1 w/ 6-core i7 CPU and 64GB RAM.

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How to monitor IO per APFS volume?

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