This section describes parameters related to ZFS memory management.
Informs the system about how much memory is reserved for application use, and therefore limits how much memory can be used by the ZFS ARC cache as the cache increases over time.
By means of this parameter, administrators can maintain a large reserve of available free memory for future application demands. The user_reserve_hint_pct parameter is intended to be used in place of the zfs_arc_max parameter to restrict the growth of the ZFS ARC cache.
Unsigned Integer (64-bit)
0
If a dedicated system is used to run a set of applications with a known memory footprint, set the parameter to the value of that footprint, such as the sum of the SGA of Oracle database.
To assign a value to the parameter, run the script that is provided in Document 1663862.1 in My Oracle Support (MOS). To make the tuning persistent across reboots, refer to script output for instructions about using –p option.
0-99
Percent
Yes
You can adjust the setting of this parameter dynamically on a running system.
For upward adjustments, increase the value if the initial value is determined to be insufficient over time for application requirements, or if application demand increases on the system. Perform this adjustment only within a scheduled system maintenance window. After you have changed the value, reboot the system.
For downward adjustments, decrease the value if allowed by application requirements. Make sure to use decrease the value only by small amounts, no greater than 5% at a time.
Unstable
Determines the minimum size of the ZFS Adaptive Replacement Cache (ARC). See also zfs_arc_max.
Unsigned Integer (64-bit)
Approximately 0.4% of total memory (physmem)
Default value to zfs_arc_max
Bytes
No
Yes, the range is validated.
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.
Unstable
Determines the maximum size of the ZFS Adaptive Replacement Cache (ARC). However, see user_reserve_hint_pct.
See also zfs_arc_min.
Unsigned Integer (64-bit)
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
Default value of zfs_arc_min to physmem
Bytes
No
Yes, the range is validated.
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.
Unstable