A customer has recently deployed an XtremIO 20 TB two X-Brick cluster to run an existing instance of Oracle RAC previously leveraging VNX for back-end storage. The application environment uses a block size of 1 MB. Multiple tables are in use with the PARALLEL_DEGREE_POLICY variable set to AUTO.
The customer wants your help with tuning the DB_FILE_MULTIBLOCK_READ_COUNT parameter for best performance with XtremIO. Which values should be recommended for tuning the DB_FILE_MULTIBLOCK_READ_COUNT parameter in the Oracle RAC environment?
Correct Answer: C
Explanation/Reference:
Oracle Database performs I/O on data files in multiples of the database block size (db_block_size), which is 8KB by default. The default Oracle Database block size is optimal on XtremIO. XtremIO supports larger block sizes as well. In the case of multiblock I/O (e.g., table/index scans with access method full), one should tune the Oracle Database initialization parameter db_file_multiblock_read_count to limit the requests to 128KB.
Therefore, the formula for db_file_multiblock_read_count is:
db_file_multiblock_read_count = 128KB / db_block_size
In our case the block size is 1 MB, so the formula db_file_multiblock_read_count is 1 MB/ 8KB = 1024/8
128
References: https://www.emc.com/collateral/white-papers/h13497-oracle-best-practices-xtremio-wp.pdf, page 21