How to set up ZFS ARC size on FreeBSD

The Adaptive Replacement Cache (ARC) is a component of the ZFS file system that stores frequently accessed data in memory to improve performance. On FreeBSD, the ARC size can be set using the “kern.vm.zfs.arc_max” sysctl.

You can check the current ARC size by running the following command:

You can set the ARC size to a specific value by running the following command:

Where “value” is the size of the ARC in bytes. For example, to set the ARC size to 4GB:

You can also set the value in human readable format using k as kilobytes, M as megabytes, G as Gigabytes etc. For example to set it to 4GB:

It is important to note that the ARC size should be set based on the amount of memory available on the system and the workloads running on it. A larger ARC size may improve performance, but it also may cause the system to use more memory, potentially leading to memory pressure.

It is also a good idea to set arc_meta_limit, which is the limit for metadata cache. It can also be set in a similar way as arc_max.

You can also add these settings to /etc/sysctl.conf so that they are automatically set at boot time.

Keep in mind that ZFS ARC size should be adjusted based on the workload, so it is always good to monitor the memory usage and adjust the settings accordingly.