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Increasing WAFL cache memory

The 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.

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 use the WAFL external cache functionality.

The 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 on high-availability (HA) configured storage systems, 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.

In addition to 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.