Tuesday, January 31, 2023

Disk Mount Conditioner

Peter Hosey:

TIL about Disk Mount Conditioner, a macOS feature like the Network Link Conditioner but for file I/O. Throttle throughput or add latency to make a device behave like something slower. See man dmc(1) for details.


The Disk Mount Conditioner is a kernel provided service that can degrade the disk I/O being issued to specific mount points, providing the illusion that the I/O is executing on a slower device. It can also cause the conditioned mount point to advertise itself as a different device type, e.g. the disk type of an SSD could be set to an HDD. This behavior consequently changes various parameters such as read-ahead settings, disk I/O throttling, etc., which normally have different behavior depending on the underlying device type.


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