ZFS ARC Parameters

This section describes parameters related to ZFS ARC behavior.

zfs_arc_min

Description

Determines the minimum size of the ZFS Adaptive Replacement Cache (ARC). See also zfs_arc_max.

Data Type

Unsigned Integer (64-bit)

Default

64 MB

Range

64 MB to zfs_arc_max

Units

Bytes

Dynamic?

No

Validation

Yes, the range is validated.

When to Change

When a system's workload demand for memory fluctuates, the ZFS ARC caches data at a period of weak demand and then shrinks at a period of strong demand. However, ZFS does not shrink below the value of zfs_arc_min. Generally, you do not need to change the default value.

Commitment Level

Unstable

Change History

For information, see zfs_arc_min.

zfs_arc_max

Description

Determines the maximum size of the ZFS Adaptive Replacement Cache (ARC). See also zfs_arc_min.

Data Type

Unsigned Integer (64-bit)

Default

75% of memory on systems with less than 4 GB of memory

physmem minus 1 GB on systems with greater than 4 GB of memory

Range

64 MB to physmem

Units

Bytes

Dynamic?

No

Validation

Yes, the range is validated.

When to Change

If a future memory requirement is significantly large and well defined, you might consider reducing the value of this parameter to cap the ARC so that it does not compete with the memory requirement. For example, if you know that a future workload requires 20% of memory, it makes sense to cap the ARC such that it does not consume more than the remaining 80% of memory.

Commitment Level

Unstable

Change History

For information, see zfs_arc_max .