Oracle ASM Administration

Oracle Automatic Storage Management (ASM) is a storage management solution for Oracle database and RAC. It allows you to create ASM disks from physical disks or partitions and multiple ASM disks form an ASM Diskgroup.

• Oracle ASM Architecture

• Oracle ASM Installation

• Oracle ASM Diskgroup Management

Oracle ASM Architecture

Oracle ASM instance is built on same architecture as Oracle Instance. There are special ASM background processes that are introduce inside Oracle database to communicate with ASM instance and diskgroups. The only difference is an Oracle database hosts your database and Oracle ASM hosts database files. Oracle ASM binaries come with Oracle Grid Infrastructure Software.

Physical Disks / Partitions: This is your hardware storage which provides raw storage capacity. Each physical disk / partition is mapped to a single ASM disk.

ASM Disks: These are disks that ASM can easily identify and you can attach ASM disks to ASM Diskgroups. One ASM Disk can be attached to one and only one ASM DIskgroup.

ASM Diskgroups: These are collection of one or more ASM disks that acts as storage location for your database files. All diskgroup name start with '+' sign: +CRS, +DATA, +FRA etc.

ASM Instance: It's the gateway through which Oracle databases can read/write to database files stored on ASM Diskgroups.

Oracle ASM Installation

Oracle ASM can be configured for a standalone Oracle database and for Oracle RAC. In a standalone ASM configuration, all your database files reside on ASM diskgroups instead of local filesystem. For Oracle RAC cluster, Oracle ASM acts as a central shared storage for all the RAC nodes. If one node goes down, the other nodes can still read/write to database files stored on ASM diskgroups.

Setup Oracle ASM for standalone database (Known as Oracle Restart)

• Install Oracle 19c with ASM

• Install Oracle 12c with ASM

• Install Oracle 11g with ASM and Data Guard

Setup Oracle ASM for RAC

• Install Oracle 11gR2 RAC on Linux

Oracle ASM Diskgroup Management

Managing data under ASM disks and diskgroups is very important task for a DBA. Let's look at different ways to administer ASM Diskgroups:

• Find ASM physical disk mapping

• Create ASM Diskgroup

• Create Tablespace in ASM

• Drop Diskgroup

• Create Directory Under ASM Diskgroup 

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 ASM Diskgroup

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;

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;

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 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;

DB_RECOVERY_FILE_DEST defines the default location for FRA

show parameter db_reocovery_file_dest
show parameter db_recovery_file_dest_size

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;

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