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Automatic Storage Management

Oracle ASM started with Oracle 10g provides volume and filesystem management where the I/O subsystem is directly handled
by the Oracle Kernel. It provides highly scalable and high availability storage instrastructure.

Each LUN is mapped as a disk. Disk are grouped together into disk group. ASM takes care of writiing / striping onto disk in the diskgroup.
i.e Database files are automatically spread over the available disks in the diskgroup it is done in extent level.

ASMCMD  ASM Command line Utility.

Its an Explorer to the ASM disk system.

1) When you execute asmcmd we get to the root of the ASM system i.e '+'
2) On executing the ls -l, you get details of the diskgroup presents.
3) With normal commands like cd,ls,du,mkdir,rm you could manipulate the ASM filesystem
Helpful Commands

du (disk usage)  :       Shows us the total disk space occupied by ASM files in that directory (and its subdirectory)
lsct                   : Information about the current ASM clients
lsdg                  : Information about the diskgroup and their attributes

State                : Current State of Diskgroup whether Mounted/Connected
Type                 : Diskgroup Redundancy (NORMAL,HIGH,EXTERNAL)
REBAL             : Y if rebalance operation in progress
Unbal               : Y is rebalancing is required by diskgroup
Sector              :  Sector size in bytes
Block                : Block size in bytes
AU                    : Allocation Unit
Total_MB           : Size of diskgroup in MB
Free_MB           : Free Space in Diskgroup
Req_mir_free_MB  : Space that is required in the diskgroup to restore full redundancy after worst failure that can be tolerated by diskgroup.
                                  (REQUIRED_MIRROR_FREE_MB column of V$ASM_DISKGROUP)
Offline_disks          : Number of offline disks in the disk group.
Name                    : Disk group name.

rm : Removes files/directory which is equivalent to "ALTER DISKGROUP ..DROP FILE/DIRECTORY"