Simulate slower disks on macOS High Sierra+

Targets macOS
1

From High Sierra, macOS includes the ‘dmc’ command (Disk Mount Conditioner) which allows you to slow down disk I/O in order to simulate working on a slower disk… because we all have a high-end 50,000$ Mac Pro :slight_smile:

Get presets:

$ dmc list 0: Faulty 5400 HDD 1: 5400 HDD 2: 7200 HDD 3: Slow SSD 4: SATA II SSD 5: SATA III SSD 6: PCIe 2 SSD 7: PCIe 3 SSD

Start a preset (n is one of the preset number above)

$ sudo dmc start / n

Stop dmc

$ sudo dmc stop /

Original article (in French): https://www.macg.co/os-x/2019/02/comment-simuler-la-presence-dun-disque-dur-dans-un-mac-equipe-dun-ssd-105231

2

High Sierra also includes APFS, I heard this also works to simulate a slower drive… :wink:

3

@Sam Rowlands: you can read my mind from half the globe away. Awesome!