For RMAN Backups to disk (D2D) with ZFS Storage Appliance, you need to review MOS Note:  1072545.1: RMAN Performance Tuning Using Buffer Memory Parameters.  
 
You can effectively optimize high-bandwidth low latency backups and restores using Oracle RMAN and the Sun ZFS Storage Appliance by adjusting the init.ora parameters that control I/O buffering.

For Oracle Exadata, you can tune the following four parameters:
• _backup_disk_bufcnt – Number of buffers used to process backup sets
• _backup_disk_bufsz – Size of the buffers used to process backup sets
• _backup_file_bufcnt – Number of buffers used to process image copies 
• _backup_file_bufsz – Size of the buffers used to process image copies

For backup operations, set the buffer size to 1 MB for backup sets and 4 MB for image copies.  Form RMAN image copies, use the following settings: 

For database restores, the buffer size should be set to 128 kB as shown below:

For RMAN database backup sets and image copies, set the number of buffers for backup sets and image copies to 64:



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