Working with Oracle Automatic Storage Management (ASM) is part of every DBA’s life. Whether you’re running a mission-critical RAC database or just managing standalone ASM for backups, you’ll eventually rely on ASMCMD — Oracle’s command-line tool for ASM.
Think of it like a UNIX shell tailored for ASM. You can list diskgroups, check attributes, mount/unmount, monitor rebalances, and even troubleshoot client connections.
Over the years, I’ve built a go-to list of ASMCMD commands that always come in handy. This post will walk you through them, with real command outputs, so you can see exactly what to expect.
1. Listing ASM Diskgroups
The first thing I usually check is which diskgroups are available:
ASMCMD> lsdg
Sample output:
State Type Rebal Sector Block AU Total_MB Free_MB Name
MOUNTED EXTERN N 512 4096 1M 102400 51200 DATA/
MOUNTED NORMAL N 512 4096 4M 204800 153600 FRA/
👉 If you want to include dismounted diskgroups:
ASMCMD> lsdg --discovery
Or list across all cluster nodes:
ASMCMD> lsdg -g --discovery
2. Exploring ASM Disks
Disks are the backbone of diskgroups. To see all available disks:
ASMCMD> lsdsk -k
Output example:
Path Size_MB Free_MB Name Failgroup Label UDID
/dev/asm-disk1 51200 25600 DATA_0001 DATA_0001 - -
/dev/asm-disk2 51200 25600 DATA_0002 DATA_0002 - -
For a specific diskgroup (CDATA)
ASMCMD> lsdsk -k -G CDATA
Output:
Path Size_MB Free_MB Name Failgroup
/dev/asm-cdata1 102400 40960 CDATA_0001 CDATA_0001
/dev/asm-cdata2 102400 40960 CDATA_0002 CDATA_0002
You can also check creation date:
ASMCMD> lsdsk -t -G CDATA
3. Checking ASM Diskgroup Attributes
Diskgroups come with attributes like allocation unit size and access control.
ASMCMD> lsattr -lm
Output:
Group_Name Name Value RO Sys
DATA au_size 1048576 Y Y
DATA cell.smart_scan_capable FALSE N N
FRA au_size 4194304 Y Y
FRA compatible.rdbms 11.2.0.0.0 N N
For a specific diskgroup (DMARCH):
ASMCMD> lsattr -lm -G DMARCH
4. Mounting and Unmounting Diskgroups
Unmount all diskgroups:
ASMCMD> umount -a
Unmount specific:
ASMCMD> umount ARCH
Mount all:
ASMCMD> mount -a
Mount one:
ASMCMD> mount ARCH
Remember: These work only on the local node. In RAC, you need to repeat on all nodes.
5. Rebalancing a Diskgroup
When disks are added/removed, ASM rebalances automatically. But you can trigger it manually:
ASMCMD> rebal --power 8 ARCH
Check progress:
ASMCMD> lsop
Output:
Group_Name Pass State Power EST_WORK EST_RATE EST_TIME
ARCH COMPACT RUN 8 1000 20000 2
6. Password File Management
Find the password file for a database:
ASMCMD> pwget --dbuniquename DBACLASS
Output:
+DATA/DBACLASS/PASSWORD/pwddbaclass.256.899912377
For ASM password file:
ASMCMD> pwget --asm
7. ASM Templates
Templates define redundancy and striping for file types.
ASMCMD> lstmpl -l -G ARCH
Output:
Group_Name Name Stripe Redund Sys
ARCH ARCHIVELOG COARSE UNPROT Y
ARCH BACKUPSET COARSE UNPROT Y
ARCH CONTROLFILE FINE MIRROR Y
8. Cluster and Version Info
Check if Flex ASM is enabled:
ASMCMD> showclustermode
ASM cluster : Flex mode disabled
Check cluster state:
ASMCMD> showclusterstate
Normal
Check version:
ASMCMD> showversion
ASM version : 19.0.0.0.0
10. Monitoring Clients
See which databases are connected to a diskgroup:
ASMCMD> lsct DMARCH
Output:
DB_Name Status Software_Version Instance_Name Disk_Group
DBACLASS CONNECTED 19.0.0.0.0 DBACLASS1 DMARCH
11. Other Useful Commands
ASM Diskstring:
ASMCMD> dsget
parameter: ORCL:*
profile: ORCL:*
List ASM users:
ASMCMD> lspwusr
Username sysdba sysoper sysasm
SYS TRUE TRUE TRUE
ASMSNMP TRUE FALSE FALSE
Open files for a diskgroup:
ASMCMD> lsof -G ARCH
Open files for a database:
ASMCMD> lsof --dbname DBACLASS
Filter driver state:
ASMCMD> afd_state
ASMCMD-9526: The AFD state is 'NOT INSTALLED' and filtering is 'DEFAULT'
List filter driver disks:
ASMCMD> afd_lsdsk
Wrapping Up
ASMCMD is more than just a tool — it’s a DBA’s daily assistant for ASM operations. Whether you’re quickly checking disk usage, confirming attributes, managing mounts, or troubleshooting, these commands save time and effort.
My advice: Practice them often. The more familiar you get, the faster you’ll diagnose and resolve ASM issues.
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