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ASM Background Processes in 11.2 (Doc ID 1641678.1)

Last updated on DECEMBER 19, 2019

Applies to:

Oracle Database - Enterprise Edition - Version to [Release 11.2]
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Cloud Exadata Service - Version N/A and later
Generic (Platform Independent)
• ASMB - ASM Background Process

Communicates with the ASM instance, managing storage and providing statistics

ASMB runs in ASM instances when the ASMCMD cp command runs or when the database instance first starts if the server parameter file is stored in ASM.
ASMB also runs with Oracle Cluster Registry on ASM.

• RBAL - ASM Rebalance Master Process

Coordinates rebalance activity

In an ASM instance, it coordinates rebalance activity for disk groups and performs a global open on ASM disks.
In a database instances, it manages ASM disk groups.

• ARBn - ASM Rebalance Process

Rebalances data extents within an ASM disk group

Possible processes are ARB0-ARB9 (ARB0, ARB1, ..) and ARBA.

• DBWR - Database Writer Process

Manages ASM buffer cache

• SMON - System Monitor Process

System monitor and communication to CSSD

• CKPT - Checkpoint Process

Manages cross instance calls in cluster setup

• PSP0 - Process Spawner Process

Spawns other ASM background processes after initial instance startup

• GMON - ASM Disk Group Monitor Process

GMON monitors all the disk groups mounted in an ASM instance

It is responsible for maintaining consistent disk membership and status information. It updates partnership and status table
Membership changes result from adding and dropping disks, whereas disk status changes result from taking disks offline or bringing them online.

Advances disk group compatibility

• MARK - Mark AU for Resynchronization Coordinator Process

Marks ASM allocation units as stale following a missed write to an offline disk
MARK essentially tracks which extents require resynchronization for offline disks.
This process runs in the database instance and is started when the database instance first begins using the ASM instance.
If required, MARK can also be started on demand when disks go offline in the ASM redundancy disk group.

• VKTM - Virtual Keeper of Time Process

Provides a wall clock time and reference time for time interval measurements
VKTM acts as a time publisher for an Oracle instance.
VKTM publishes two sets of time: a wall clock time using a seconds interval and a higher resolution time (which is not wall clock time) for interval measurements.
The VKTM timer service centralizes time tracking and offloads multiple timer calls from other clients.

• LGWR - Log Writer Process

Copies logging information to an ASM diskgroup.

• Onnn - ASM Connection Pool Process

Maintains a connection to the ASM instance for metadata operations
Onnn slave processes are spawned on demand. These processes communicate with the ASM instance.

Represents the server side of a client/server connection.

These processes will appear the moment the instance is started, and
will disappear after that.

• bnnn - ASM Blocking Slave Process for GMON

Performs maintenance actions on ASM disk groups.

Slave used to process offline disks.

Bnnn performs actions that require waiting for resources on behalf of GMON. GMON must be highly available and cannot wait.
A Bnnn slave is spawned when a disk is taken offline in an ASM disk group. Offline timer processing and drop of the disk are performed in this slave.
Up to five process (B000 to B004) can exist depending on the load.

• xnnn - ASM Disk Expel Slave Process

Performs ASM post-rebalance activities

This process expels dropped disks at the end of an ASM rebalance.

• VDBG - Volume Driver Process

Forwards ASM requests to perform various volume-related tasks
VDBG handles requests to lock or unlock an extent for rebalancing, volume resize, disk offline, add or drop a disk, force and dismount disk group to the Dynamic Volume Manager driver.

• VBGn - Volume Background Process

Communicates between the ASM instance and the operating system volume driver

VBGn handles messages originating from the volume driver in the operating system and sends them to the ASM instance.
VBGn can run as multiple processes, where n is 0-9.

Opens or closes an ASM volume for mount/dismount operations.

• VMB Volume Membership Process

Maintains cluster membership on behalf of the ASM volume driver
This process membership in the cluster as an I/O-capable client on behalf of the ASM volume driver.


 The note provides reference for ASM background processes


This note is intended for dbas, and system administrators


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