ASM Diks:Diskgroup and Diskgroup Attributes

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Understanding ASM Disk:Diskgroup and Diskgroup Attributes

In this post I will give you a brief idea about ASM components. The post is helpful for beginners to understand the ASM and Its components

ASM Disks

To create ASM disk group you need valid ASM disks. Valid ASM disks can be
A Disk Partition
A Logical Unit Number (LUN)
A Logical Volume
A Network File System (NFS)

Here is an Example of Valid ASM Disk. You need correct permissions on these disks so that ASM can read them. I have ASM  AFD configured in my environment and therefore the below permissions are correct for me

[root@TEST05]# ls -lrt /dev/xvd*
brw-rw---- 1 root disk 202,  64 Jun  4 12:41 /dev/xvde
brw-rw---- 1 root disk 202,  48 Jun  4 12:41 /dev/xvdd
brw-rw---- 1 root disk 202,  32 Jun  4 12:41 /dev/xvdc
brw-rw---- 1 root disk 202,  80 Jun  4 12:41 /dev/xvdf
brw-rw---- 1 root disk 202, 160 Jun  4 12:41 /dev/xvdk

ASM Diskgroup

ASM groups the disks in Diskgroup. A disk group can have 1 or more (from 12c and later maximum 10,000 disks )disks. You can create a DG using ASMCMD/ASMCA/SQLPLUS or OEM utility.

ASM Diskgroup Attributes

Disk group attributes are parameters that are bound to a disk group, rather than an Oracle ASM instance. Some disk group attributes can be set when a disk group is created or altered. Other disk attributes can only be set when a disk group is created or only be set when a disk group is altered

How to List ASM Diskgroup Attributes

You can use asmcmd lsattr or v$asm_attribute view to display the ASM diskgroup attributes

$asmcmd lsattr <= lists all available ASM diskgroup attributes

Synopsis
        lsattr [-G <diskgroup> ] [-lm] [--suppressheader] [<pattern>]

Description
        The options for the lsattr command are described below.

        -G diskgroup     - Disk group name.
        -l               - Display names with values.
        -m               - Displays additional information, such as the RO
                           and Sys columns.
        --suppressheader - Suppresses column headings.
        pattern          - Display the attributes that contain pattern
                           expression.

Listing only the Diskgroup Attributes Having Values for a Particular DG

ASMCMD>  lsattr -l -G DG_TEST

Apply Filter while Listing the Diskgroup Attributes

You can even apply filter to filter out only desired attributes

ASMCMD>  lsattr -l -G DG_TEST scrub*

How to Configure ASM Diskgroup Attribute

You can configure the ASM diskgroup attributes either using asmcmd setattr command or alter diskgroup command from ASM Instance

Synopsis
        setattr -G <diskgroup> <attribute_name> <attribute_value>

Description
        The options for the setattr command are described below.

        -G diskgroup    - Disk group name.
        attribute_name  - Name of the attribute.
        attribute_value - Value of the attribute.

ASMCMD>  lsattr -l -G DG_TEST_DATA compatible*
Name              Value
compatible.advm   12.2.0.1.0
compatible.asm    12.2.0.1.0
compatible.rdbms  10.1.0.0.0
ASMCMD>  setattr  -G DG_TEST_DATA compatible.rdbms 12.2.0.1.0
ASMCMD>  lsattr -l -G DG_TEST_DATA compatible*Name              Value
compatible.advm   12.2.0.1.0
compatible.asm    12.2.0.1.0
compatible.rdbms  12.2.0.1.0

SQL> select NAME,VALUE from  v$asm_attribute where GROUP_NUMBER=1 and NAME like '%repair%';

NAME                           VALUE
------------------------------ ----------------------------------------
disk_repair_time               3.6h
failgroup_repair_time          24.0h

SQL> alter diskgroup DG_TEST_DATA set attribute 'disk_repair_time'='5h';

Diskgroup altered.

SQL> select NAME,VALUE from  v$asm_attribute where GROUP_NUMBER=1 and NAME like '%repair%';

NAME                           VALUE
------------------------------ ----------------------------------------
disk_repair_time               5h
failgroup_repair_time          24.0h

ASM Instance

An ASM instance is similar to a Database Instance. It is used to mount the Diskgroup and provide the access of the diskgroup (storage) to the database. The metadata ASM uses to control the diskgroups resides in the DG itself