Here is a short note on ASM background processes and their purpose in managing Oracle ASM instances.
|ASMB||ASM Background Process|
|RBAL||ASM Rebalance Master Process|
|ARBn||ASM Rebalance Process|
|DBWR||Database Writer Process|
|SMON||System Monitor 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.
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