Oracle ASM Administration

Managing data under ASM disks and diskgroups is very important task for a DBA. In this article, we will be looking at general ASM administration tasks you must know.

• Create Directory Under ASM Diskgroup

• Find ASM physical disk mapping

• Create Diskgroup ASM

• Create Tablespace in Oracle ASM

  
  

• Drop Diskgroup

Create Directory Under ASM Diskgroup

Creating directories under ASM filesystem is same as running Linux commands. Start asmcmd

asmcmd

You can use many OS level commands like

• ls – to list contents

• pwd – check present working directory

• mkdir – create new directory

• rm – remove directory or file

• cp – copy file or directory

ASMCMD> ls
CRSVOL1/
DATAVOL1/
FRAVOL1/
RMANVOL/

Let us create directory under RMANVOL diskgroup

ASMCMD> cd RMANVOL/
ASMCMD> mkdir RMAN_BACKUP
ASMCMD> mkdir RMAN_SCRIPT
ASMCMD> mkdir RMAN_LOG

You can create multiple directories in one single command too

ASMCMD> mkdir RMAN_BACKUP RMAN_SCRIPT RMAN_LOG

Find ASM physical disk mapping

When you work in a RAC environment with a list of ASM disks, sometimes you might want to figure out which ASM disk is mapped to which physical device. Below is a simple script that will help you find out ASM disks that are mapped to Linux partitions

#!/bin/bash
echo "------------------"
echo "ASM Disk Mappings"
echo "------------------"
for f in $(oracleasm listdisks); do
    dp=$(lsblk | grep $(oracleasm querydisk -d $f | awk -F'[][]' '{gsub(/,/ , ":"); print $2}') | awk '{print $1, "size", $4}' | tr -d '`' | sed 's/[-|]//g')
    echo -e "$f\tmapped to /dev/$dp"
done

And below is the sample output

------------------
ASM Disk Mappings
------------------
CRS01	mapped to /dev/sdb1 size 5G
DATA01	mapped to /dev/sdb2 size 50G
FRA01	mapped to /dev/sdb3 size 80G

Create Diskgroup ASM

There are two ways to create new diskgroups in ASM: ASMCA (GUI) and SQLPLUS (SQL Syntax). As root user, mark the disk headers which you will be attaching to the diskgroup

oracleasm createdisk RMAN01 /dev/sdc1

As grid user, connect to sqlplus and check if above created disk is available

sqlplus / as sysasm

SELECT NAME, PATH, HEADER_STATUS FROM V$ASM_DISK;

The HEADER_STATUS must show as PROVISIONED.

Create diskgroup with EXTERNAL REDUNDANCY

CREATE DISKGROUP RMAN EXTERNAL REDUNDANCY
DISK '/dev/oracleasm/disks/rman01';

Create Normal Redundancy Diskgroup

Redundancy is defined by failgroups inside a diskgroup. You need to add at lease two failgroups when creating normal redundancy disk group. All the disks that you would like to attach shall belong to respective failgroups.

Everytime ASM is writing to one failgroup, it create a copy of the same data into another failgroup. If any failgroup is not available, ASM retrieves the data from the available failgroup.

As root user, mark the disk headers which you want to attach

oracleasm createdisk OLTP01 /dev/sdd1
oracleasm createdisk OLTP02 /dev/sdd2

As grid user, connect to sqlplus and check if above created disk is available

sqlplus / as sysasm

SELECT NAME, PATH, HEADER_STATUS FROM V$ASM_DISK;

The HEADER_STATUS must show as PROVISIONED.

Create diskgroup with NORMAL REDUNDANCY

CREATE DISKGROUP OLTP NORMAL REDUNDANCY
FAILGROUP OLTP_FG1 DISK '/dev/oracleasm/disks/oltp01'
FAILGROUP OLTP_FG2 DISK '/dev/oracleasm/disks/oltp02';

Create High Redundancy Diskgroup

For high redundancy, you need at least 3 failgroups. As root user, mark the disk headers which you want to attach

oracleasm createdisk BACKUP01 /dev/sde1
oracleasm createdisk BACKUP02 /dev/sde2
oracleasm createdisk BACKUP03 /dev/sde3

Create diskgroup with EXTERNAL REDUNDANCY

CREATE DISKGROUP BACKUP EXTERNAL REDUNDANCY
FAILGROUP BACKUP_FG1 DISK '/dev/oracleasm/disks/backup01'
FAILGROUP BACKUP_FG2 DISK '/dev/oracleasm/disks/backup02'
FAILGROUP BACKUP_FG3 DISK '/dev/oracleasm/disks/backup03';

Change Diskgroup Redundancy

You cannot directly change the redundancy of diskgroup. Instead create a new diskgroup with desired redundancy and move datafiles. You can simply use below command to move datafile from 12c version and above

alter database move datafile '+DATA/ORCL/DATAFILE/user01.dbf' to '+NEWDG';

Create Tablespace in Oracle ASM

ASM uses OMF (Oracle Managed Files) feature of Oracle database to auto create datafiles in respective ASM diskgroups. The DB_CREATE_FILE_DEST defines the default location where Oracle creates datafiles

Show parameter db_create_file_dest;

Make sure db_create_file_dest is set to +DATA

DB_RECOVERY_FILE_DEST defines the default location for FRA

show parameter db_reocovery_file_dest
show parameter db_recovery_file_dest_size

Make sure db_reocovery_file_dest is set to +FRA

Create new tablespace with 10 gb size

SQL> CREATE TABLESPACE test_tbs DATAFILE SIZE 10G;

You can manually give datafile name too

SQL> CREATE TABLESPACE test_tbs datafile '+ASM/DATAFILES/ORCL/test_tbs.dbf' size 10G;

Drop Diskgroup

To drop a diskgroup including all the files on the ASM disks

DROP DISKGROUP RMAN INCLUDING CONTENTS;