Creating ASM Disk Groups without Using DBCA
If I am using DBCA to create my sample ASM instance, Oracle
formats the commands necessary to create the initial ASM disk group(s) for the
instance during its creation. However, I can also create the ASM disk groups
separately after the necessary instance creation scripts have run successfully
using the code shown in Listing
2.3. I have provided two different examples, one each for the Windows
NT and Linux environments.
Starting and Stopping an ASM Instance
An ASM instance is managed in much the same way as a
database instance, with a few exceptions. The major difference is that an ASM
instance is never opened like a regular Oracle instance is opened, only mounted;
therefore, I will either issue the STARTUP NOMOUNT; command to start just the ASM
instance's memory processes, and then finish mounting the database with the ALTER DATABASE MOUNT;
command. I can also open the ASM instance immediately by issuing the STARTUP MOUNT;
command.
Starting a Dormant ASM Instance. To start up a
dormant ASM instance, I first have to remember to set the ORACLE_SID environment
variable appropriately. In addition, before I can start the ASM instance in the
Windows NT environment, I also need to remember to first start the Oracle
Cluster Service as well as the ASM instance's service. Of course, I do not need
to worry about this in the Linux environment – the Cluster Service should have
already been set up as part of the standard Linux installation of Oracle 10g.
To start up the ASM instance, I then simply issue the STARTUP MOUNT
command. Here is how a successful ASM instance startup appears in the Linux
environment:
$> export ORACLE_SID=+ASM
$> sqlplus "sys as sysdba"
SQL*Plus: Release 10.1.0.2.0 - Production on Tue Dec 13 16:58:17 2005
Copyright (c) 1982, 2004, Oracle. All rights reserved.
Enter password: ********
Connected to an idle instance.
SQL> startup mount;
ASM instance started
Total System Global Area 100663296 bytes
Fixed Size 787648 bytes
Variable Size 99875648 bytes
Database Buffers 0 bytes
Redo Buffers 0 bytes
ASM diskgroups mounted
Shutting Down an Active ASM Instance. To shut down
this ASM instance, I once again set the ORACLE_SID environment variable and then simply
issue the SHUTDOWN IMMEDIATE;
command:
$> export ORACLE_SID=+ASM
$> sqlplus "sys as sysdba"
SQL> Connected.
SQL> shutdown immediate;
ASM diskgroups dismounted
ASM instance shutdown
SQL>
Implications of Shutting Down an Active ASM Instance. Now,
a warning: When an ASM instance is shut down, it is important to be aware of
the implications for any regular Oracle database instance that is using ASM
files stored on that ASM instance. The ASM files will not be accessible to
those regular Oracle databases until the ASM instance is restarted.
Demonstrating ASM in a Sample Database
Now that I have explained how to create, start, and stop an
ASM instance, I will next demonstrate how to add a tablespace to an existing
Oracle database instance that uses the ASM instance's disk group instead of the
database instance's disk storage to store the new tablespace's datafile.
Creating an ASM-Managed Tablespace. What I really
like about ASM is its simplicity. I no longer need to be concerned if the
tablespace's datafile will fit on the drive or spindle I have targeted for
storage; I simply inform ASM that it is responsible for storing the datafile
and how large the datafile is, and ASM handles the rest.
All I needed to do to create a new tablespace, TBS_ASM1, was
to issue the following CREATE TABLESPACE
command from a SQL*Plus session running against the database instance:
SQL> CREATE TABLESPACE tbs_asm1 DATAFILE '+DGROUP1' SIZE 32M;
Tablespace created.
Note that I did not have to specify the exact location of
the datafile, since ASM determined from the size of the tablespace exactly how
it should be striped across the disks in the ASM disk group. Moreover, since
ASM uses Oracle Managed Files (OMF) for naming the datafile, ASM automatically
named the datafile using the appropriate OMF standard. (I will delve into ASM
file naming conventions in greater detail in the next article in this series.)
Even more interesting, I did not have to do anything special
to inform the database instance that it needed to start up the appropriate
Rebalancing (RBAL) and ASM Bridge (ASM) processes. As soon as this new
tablespace was created, the database instance detected that ASM storage was in
use, and it automatically started these two background processes, as this
snippet from the database's alert log clearly shows:
...
Sun Dec 11 18:35:00 2005
CREATE TABLESPACE tbs_asm1 DATAFILE '+DGROUP1' SIZE 32M
Sun Dec 11 18:35:03 2005
Starting background process ASMB
ASMB started with pid=21, OS id=776
Starting background process RBAL
RBAL started with pid=22, OS id=3524
Sun Dec 11 18:35:09 2005
SUCCESS: diskgroup DGROUP1 was mounted
Completed: CREATE TABLESPACE tbs_asm1 DATAFILE '+DGROUP1' SIZ
...
Migrating an Existing Tablespace to ASM-Managed Storage.
Another great thing about ASM: I did not have to recreate an existing
tablespace when I wanted to migrate it to ASM storage. Instead, I used Recovery
Manager (RMAN) to create an image copy of the tablespace's datafile, and
then I simply migrated that datafile to ASM. To demonstrate, I created
a new tablespace in the database instance. I then issued the appropriate RMAN
commands to take the tablespace offline, create the image copy of the
tablespace, transfer the tablespace to ASM, and then bring the tablespace back
online. See Listing
2.4 for the SQL statements and RMAN commands that I used to complete
this task.
Setting Up Enterprise Manager (EM) for ASM Instance Management
Oracle 10g Enterprise Manager (EM) does provide a simple and
elegant way to manage ASM storage; however, I needed to reconfigure my database
instance's EM configuration to take advantage of these tools via the Enterprise
Manager Configuration Assistant (EMCA). Once I had created the ASM instance and
had then created at least one ASM-managed file in my database instance, I
removed the original EM configuration for the database instance and then
replaced it with a new EM configuration that fully supports ASM. A sample set
of EMCA commands are shown in Listing
2.5.
After I restarted the EM Database Console service for my
database, I was then able to view details about the ASM instance as well by
clicking on the ASM link on my database instance's home page (see Figure 2.3 for
an example of that screen). I will explore the various diagnostic tools and
maintenance operations available via EM in more detail in the next article in
this series.
Viewing ASM Instance Information Via SQL Queries
Finally, there are several dynamic and data dictionary views
available to view an ASM configuration from within the ASM instance itself:
|
ASM Dynamic Views: ASM
Instance Information
|
|
View Name
|
Description
|
|
V$ASM_ALIAS
|
Shows every alias for
every disk group mounted by the ASM instance
|
|
V$ASM_CLIENT
|
Shows which database
instance(s) are using any ASM disk groups that are being mounted by this
ASM instance
|
|
V$ASM_DISK
|
Lists each disk
discovered by the ASM instance, including disks that are not part
of any ASM disk group
|
|
V$ASM_DISKGROUP
|
Describes information about ASM
disk groups mounted by the ASM instance
|
|
V$ASM_FILE
|
Lists each ASM file
in every ASM disk group mounted by the ASM instance
|
|
V$ASM_OPERATION
|
Like its counterpart,
V$SESSION_LONGOPS, it shows each long-running ASM operation in the ASM
instance
|
|
V$ASM_TEMPLATE
|
Lists each template present
in every ASM disk group mounted by the ASM instance
|
I was also able to query the following dynamic views against
my database instance to view the related ASM storage components of that
instance:
|
ASM Dynamic Views: Database
Instance Information
|
|
View Name
|
Description
|
|
V$ASM_DISKGROUP
|
Shows one row per each ASM
disk group that's mounted by the local ASM instance
|
|
V$ASM_DISK
|
Displays one row per each
disk in each ASM disk group that are in use by the database instance
|
|
V$ASM_CLIENT
|
Lists one row per each
ASM instance for which the database instance has any open ASM files
|
See Listing
2.6 for the SQL*Plus queries that I used to view information from the
ASM and database instances.
Next Steps
The next article in this series will concentrate on some
of the more advanced features of ASM, including how to add disks to and remove
disks from an ASM disk group, how to increase the survivability of ASM disk
groups with additional striping and mirroring features, and how to monitor
and manage ASM storage through the Enterprise Manager (EM) interface.
References and Additional Reading
While there is no substitute for direct experience, reading
the manual is not a bad idea, either. I have drawn upon the following Oracle
10g documentation for the deeper technical details of this article:
B10130-02 Oracle Database
Installation Guide 10g (10.1.0.2) For Windows, Section 2.5.3
B10739-01 Oracle Database
Administrator's Guide, Chapter 12
B10743-01 Oracle Database
Concepts, Chapter 14
B10755-01 Oracle Database
Reference
B10759-01 Oracle Database
SQL Reference
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