Oracle RAC ASM Disk Space 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.

To ensure that a disk group always has sufficient space to store the critical organizational data, you will have to continuously track the space usage of the disk group. This will provide you with early pointers to potential space contentions and help you swiftly provide more space to the group by adding more disks. The ASM Disk Space test enables you to achieve this end. This test closely monitors how each disk in a disk group uses the space available to it, points you to the disks that are running out of space, and thus holds a mirror to space contentions on a disk group.

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 Cluster 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 RAC

Agent deploying the test : An internal agent

Outputs of the test : One set of results for each DiskGroup:Disk pair on the Oracle server 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. ORACLE HOME - By default, this test auto-discovers the full path to the Oracle installation directory. This is why, the ORACLE HOME parameter is set to none by default.
  6. USE ASM INSTANCE - By default, this flag is set to No indicating that the eG agent is capable of extracting the metrics related to the space utilization of the ASM disks from the ORASID. In some environments, the ORASID may provide outdated metrics. In such cases, set this flag to Yes so that the eG agent can extract the metrics using the name of the ASM instance instead of the ORASID.
  7. 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 specifying a valid service name, 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’

  8. 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>;

    If the ORACLE HOME is set to none and the USE ASM INSTANCE flag is set to Yes, then, the user monitoring the Oracle database server should be vested with an additional SYSDBA privilege. To provide this privilege, do the following:

    grant sysdba to user <user_name>;

    The name of this user has to be specified here.

  9. Password – Password of the specified database user
  10. Confirm password – Confirm the password by retyping it here.
  11. ISPASSIVE – If the value chosen is yes, then the Oracle server under consideration is a passive server in an Oracle cluster. No alerts will be generated if the server is not running. Measures will be reported as "Not applicable" by the agent if the server is not up.
Measurements made by the test
Measurement Description Measurement Unit Interpretation

Used space:

Indicates the amount of space currently used in this disk.

MB

Ideally, the value of this measure should be low. A consistent increase in this value is a cause for concern.

Free space:

Indicates the amount of space in this disk that is currently free - i.e., available for use.

MB

Ideally, the value of this measure should be high. A consistent decrease in this value is a cause for concern.

Space availability:

Indicates the percentage of space in this disk that is currently unused.

 

Percent

A high value is typically desired for this measure. By comparing the value of this measure across disks and across disk groups, you can quickly isolate the disks/groups that are running short of space. If the free space is alarmingly low for all disks in a group, it indicates that the group requires more space. You can then consider making space by adding more disks to the group.

Space usage:

Indicates the percentage of space in this disk that is currently used.

 

Percent

A low value is typically desired for this measure. By comparing the value of this measure across disks and across disk groups, you can quickly isolate the disks/groups that are utilizing space excessively. If the used space is alarmingly high for all disks in a group, it indicates that the group is rapidly running out of space. You can then consider making space by adding more disks to the group.

Used space growth:

Indicates the growth in space usage of this disk since the last measurement period.

MB/Sec

If you observe the variations to this measure over time, you will be able to detect early whether the space in the disk is being steadily eroded or not. This way, you can initiate measures to conserve space much before the disk exhausts all the space available to it.

If you observe the variations to this measure over time, you will be able to detect early whether the space in the disk is being steadily eroded or not. This way, you can initiate measures to conserve space much before the disk exhausts all the space available to it.