Oracle RAC ASM Disk I/O Test

ASM is a volume manager and a file system for Oracle database files that supports single-instance Oracle Database and Oracle Real Application Cluster (Oracle RAC) configuration. ASM is Oracle’s recommended storage management solution that provides an alternative to conventional volume managers, file systems, and raw devices.

ASM uses disk groups to store datafiles; an ASM disk group is a collection of disks that ASM manages as a unit. Within a disk group, ASM exposes a file system interface for Oracle database files. The content of files that are stored in a disk group are evenly distributed, or striped, to eliminate hot spots and to provide uniform performance across the disks.

You need to periodically monitor the read-write activity on each disk in a disk group to make sure that I/O load is uniformly balanced across all disks in a group. The ASM Disk I/O test helps you do just that. At pre-configured intervals, this test monitors the I/O activity on each disk in every disk group of an Oracle cluster, reveals I/O-intensive and error-prone disks, and brings irregularities in load balancing to the fore.

This test is disabled by default. To enable the test, go to the enable / disable tests page. To access this page, follow the Tests -> Enable/Disable menu sequence in the Agents tile of the Admin tile menu. In the enable/disable tests page, pick Oracle RAC as the Component type, Performance as the Test type, choose this test from the disabled tests list, and click on the < button to move the test to the ENABLED TESTS list. Finally, click the Update button.

Target of the test : Oracle Cluster

Agent deploying the test : An internal agent

Outputs of the test : One set of results for each DiskGroup:Disk pair in the Oracle cluster being monitored

Configurable parameters for the test
  1. TEST PERIOD - How often should the test be executed
  2. Host – The host for which the test is to be configured
  3. Port - The port on which the server is listening
  4. orasid - The variable name of the oracle instance
  5. service name - A ServiceName exists for the entire Oracle RAC system. When clients connect to an Oracle cluster using the ServiceName, then the cluster routes the request to any available database instance in the cluster. By default, the service name is set to none. In this case, the test connects to the cluster using the orasid and pulls out the metrics from that database instance which corresponds to that orasid. If a valid service name is specified instead, then, the test will connect to the cluster using that service name, and will be able to pull out metrics from any available database instance in the cluster.

    To know the ServiceName of a cluster, execute the following query on any node in the target cluster:

    select name, value from v$parameter where name =’service_names’

  6. User – In order to monitor an Oracle RAC, a special database user account has to be User – In order to monitor an Oracle database server, a special database user account has to be created in every Oracle database instance that requires monitoring. A Click here hyperlink is available in the test configuration page, using which a new oracle database user can be created. Alternatively, you can manually create the special database user. When doing so, ensure that this user is vested with the select_catalog_role and create session privileges.

    The sample script we recommend for user creation (in Oracle database server versions before 12c) for eG monitoring is:

    create user oraeg identified by oraeg create role oratest;

    grant create session to oratest;

    grant select_catalog_role to oratest;

    grant oratest to oraeg;

    The sample script we recommend for user creation (in Oracle database server 12c) for eG monitoring is:

    alter session set container=<Oracle_service_name>;

    create user <user_name>identified by <user_password> container=current default tablespace <name_of_default_tablespace> temporary tablespace <name_of_temporary_tablespace>;

    Grant create session to <user_name>;                                 

    Grant select_catalog_role to <user_name>;

    The name of this user has to be specified here.

  7. Password – Password of the specified database user
  8. Confirm password – Confirm the password by retyping it here.
Measurements made by the test

Measurement

Description

Measurement Unit

Interpretation

Reads:

Indicates the rate at which reads occur on this disk.

Reads/Sec

Compare the values of each of these measures across the disks in a disk group to identify the I/O-intensive disks in that group. In the process, you can also determine whether/not I/O load is equally balanced across all the disks in the group. If any irregularities are noticed in load-balancing are noticed, you may want to consider adding more disks to the group.

Writes:

Indicates the rate at which writes occur on this disk.

Writes/Sec

Read errors:

Indicates the number of errors that occur per second while reading from this disk.

 

ReadErrors/Sec

The value 0 is desired for both these measures. A non-zero value is indicative of I/O errors. By comparing the values of each of these measures across disks and across disk groups, you can not only point to the error-prone disks and groups, but can also figure out when most of the errors occurred on the disk/group - when reading? or when writing?

Write errors:

Indicates the number of errors that occur per second when writing to this disk on this cluster node.

WriteErrors/Sec