IO Subsystem Panel
This panel shows information relating to the shared storage subsystem for the Oracle RAC cluster.
Some of this information is aggregated from queries sent to the individual instances; other information is obtained from a single query to one of the instances.
The ASM spinner is populated only when ASM (Automatic Storage Management) is being used. Connect to Spotlight on Oracle RAC
The flows between the I/O Subsystem panel and the individual instances represent the flow of physical reads and writes between the instances and the physical database.
ASM
If installed, Oracle's Automatic Storage Management (ASM) system automatically stores and reorganizes data according to statistics collected from usage and user access patterns. The IO Subsystem panel displays this ASM metric:
| Metric | Description |
|---|---|
| Activity |
Automatic Storage Management (ASM) is a storage management solution from Oracle Corporation that automatically reorganizes data based on statistics collected from usage and user access patterns over time. The value of this component indicates the total I/O activity on the ASM instance. ASM can support more than one database, and so the I/O per second metric reflects the total I/O for the ASM instance, which includes ASM activities such as internal re-organization and I/O operations for other databases configured to access ASM on the same node. |
Data Files
The Data Files area of the panel displays the following metrics for the RAC database cluster.
| Metric | Description |
|---|---|
| Phys Reads |
The rate of physical reads performed across ALL instances in the Oracle RAC cluster. In an Oracle RAC cluster, blocks are shared between instances. When a user session needs a block, it will search for the block in the buffer of the local instance first; if the block is not found there, the user session then looks for it in the buffer cache of all other participating instances. A physical read (where data is read from disk) is required only when the block is not found in the buffer cache of ANY of the instances. |
| Phys Writes | The rate of physical writes performed across all instances in the Oracle RAC cluster. |
| Single Block Read Service Time | The time taken to read a single block into memory from a datafile on each instance. |
| Files | The total number of data files in the Oracle RAC cluster. |
| Tablespaces | The total number of tablespaces in the Oracle RAC cluster. |
| Total | The total size of tablespaces in the Oracle RAC cluster. |
Redo Logs
The Redo Logs area of the panel displays the following metrics for the RAC database cluster.
| Metric | Description |
|---|---|
| Redo Writes | The rate of redo writes performed to the Log Writer (LGWR) in an Oracle RAC cluster. This is the rate of total redo writes from all instances participating in the cluster. |
| Groups | The average and maximum number of groups in the Redo logs for the Oracle RAC cluster. |
| Size | The average and maximum size of Redo logs in the Oracle RAC cluster. |
Archive Logs
The Archive Logs area of the panel displays the following metrics for the RAC database cluster.
| Metric | Description |
|---|---|
| Cylinder |
This information is updated every 5 minutes. This value shows the aggregate amount of free space available in the archive destinations defined for the Oracle database. There are usually at least two (and there can be as many as 10) archive destinations defined per Oracle instance. A destination failure occurs when the next archive destination is about to fail. A critical failure occurs when the number of working archive destinations falls below the minimum number needed to archive successfully. Notes:
For more information on archive log space for this Oracle RAC cluster, see the Archive Destinations | Free Space chart and Archive Destination grid. |
| Total Size | The total amount of space on the archive destination whose failure will cause the archiving process to fail (critical failure) |
| Minimum Free |
The amount of free space left on the archive destination whose failure will cause the archiving process to fail (critical failure). Note (Oracle 10g and later): When ASM is used for archiving, a negative value for the Minimum Free metric indicates that the ASM diskgroup does not have enough space to cope with a disk failure. |
| Time to failure |
The time at which the archiving process will fail if the relevant archive log destination(s) are not purged (critical failure ). Note: Spotlight calculates the time to failure via the V$ARCHIVED_LOG table, and returns no estimate until that table contains at least 7 logs. For more information on archive log space for the Oracle RAC cluster, see the Archive Destinations | Free Space chart and Archive Destination grid. |
System Information
The System Information area below the IO Subsystem panel contains details of the Oracle version and operating system version.
The Uptime for the Oracle RAC cluster is that of the database instance with the longest uptime. This may underestimate the actual uptime of the cluster.