OCP 1Z0 053 254

254.Which three statements correctly describe the features of the I/O calibration process? (Choose 
three.) 
A. Only one I/O calibration process can run at a time. 
B. It automates the resource allocation for the Automated Maintenance Tasks. 
C. It improves the performance of the performance-critical sessions while running. 
D. It can be used to estimate the maximum number of I/Os and maximum latency time for the system. 
E. The latency time is computed only when the TIMED_STATISTICS initialization parameter is set to 
TRUE.  
Answer: ADE 

http://docs.oracle.com/cd/E11882_01/server.112/e41573/iodesign.htm#PFGRF94383

8.3.1 Prerequisites for I/O Calibration

Before running I/O calibration, ensure that the following requirements are met:

• The user must be granted the SYSDBA privilege

• timed_statistics must be set to TRUE

• Asynchronous I/O must be enabled

  When using file systems, asynchronous I/O can be enabled by setting the FILESYSTEMIO_OPTIONS initialization parameter toSETALL.

• Ensure that asynchronous I/O is enabled for data files by running the following query:

  COL NAME FORMAT A50SELECT NAME,ASYNCH_IO FROM V$DATAFILE F,V$IOSTAT_FILE IWHERE  F.FILE#=I.FILE_NOAND    FILETYPE_NAME='Data File';

Additionally, only one calibration can be performed on a database instance at a time.

8.3.2 Running I/O Calibration

The I/O calibration feature of Oracle Database is accessed using the DBMS_RESOURCE_MANAGER.CALIBRATE_IO procedure. This procedure issues an I/O intensive read-only workload, made up of one megabyte of random of I/Os, to the database files to determine the maximum IOPS (I/O requests per second) and MBPS (megabytes of I/O per second) that can be sustained by the storage subsystem.

The I/O calibration occurs in two steps:

• In the first step of I/O calibration with the DBMS_RESOURCE_MANAGER.CALIBRATE_IO procedure, the procedure issues random database-block-sized reads, by default, 8 KB, to all data files from all database instances. This step provides the maximum IOPS, in the output parameter max_iops, that the database can sustain. The value max_iops is an important metric for OLTP databases. The output parameter actual_latency provides the average latency for this workload. When you need a specific target latency, you can specify the target latency with the input parameter max_latency (specifies the maximum tolerable latency in milliseconds for database-block-sized IO requests).

• The second step of calibration using the DBMS_RESOURCE_MANAGER.CALIBRATE_IO procedure issues random, 1 MB reads to all data files from all database instances. The second step yields the output parameter max_mbps, which specifies the maximum MBPS of I/O that the database can sustain. This step provides an important metric for data warehouses.