Increasing WAFL cache memory

You can increase Write Anywhere File Layout (WAFL) cache memory in a system that has a caching module installed (Performance Acceleration Module (PAM), Flash Cache module, or Flash Cache 2 module). To increase the WAFL cache memory, you use the WAFL external cache, a software component of Data ONTAP.

WAFL external cache provides extra WAFL cache memory to improve the performance of the storage system by reducing the number of disk reads. You can control how user data blocks are cached by changing the mode of operation for a caching module. You can keep the default mode (normal user data blocks) or you can choose metadata mode or low-priority blocks mode.

To change the mode, you need to use the Data ONTAP CLI by running the nodeshell options flexscale commands. For more information, see the Clustered Data ONTAP System Administration Guide for Cluster Administrators.

You should verify that the WAFL external cache functionality is enabled after you install a caching module.

Note: WAFL external cache does not require a separate license if your system is running Data ONTAP 8.1 or later.

Note: Not all systems have a caching module installed. Therefore, not all systems can utilize the WAFL external cache functionality.

WAFL external cache does not cache data that is stored in a RAID group composed of SSDs.

If you use WAFL external cache on storage systems with a high-availability configuration, you must ensure that the WAFL external cache options are the same on both nodes. Otherwise, a takeover can result in lower performance due to the lack of WAFL external cache on the remaining node.

Besides the Data ONTAP options that you can use to manage WAFL external cache, a diagnostic command is available for sanitizing a caching module. For more information, see the Diagnostics Guide.