The snapshot journal should typically be between 10 and 30 percent of the total size of the protected volumes. Smaller snapshot journals are appropriate when snapshots are not kept for a long time and when production I/O is light. Larger snapshot journals are necessary when you want to keep snapshots for an extended period of time and when heavy production I/O activities are required.
Note: You can also use the Sizing tool to calculate write journal pool size. For more information, refer to Using the Sizing Tool to Calculate LFC Size.