ASM background processes in 11gR2

Here is a short note on ASM background processes and their purpose in managing Oracle ASM instances.

Background Process	Description
ASMB	ASM Background Process
RBAL	ASM Rebalance Master Process
ARBn	ASM Rebalance Process
DBWR	Database Writer Process
SMON	System Monitor Process
CKPT	Checkpoint Process
PSP0	Process Spawner Process
GMON	ASM Disk Group Monitor Process
MARK	Mark AU for Resynchronization Coordinator Process
VKTM	Virtual Keeper of Time Process
LGWR	Log Writer Process
Onnn	ASM Connection Pool Process
bnnn	ASM Blocking Slave Process for GMON
xnnn	ASM Disk Expel Slave Process
VDBG	Volume Driver Process
VBGn	Volume Background Process
VMB	Volume Membership Process

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 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 processes (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.