Database Reference
In-Depth Information
Quick ASM Overview
Automatic Storage Management (ASM)
provides a centralized way to manage Oracle
Database disk storage. ASM is designed to simplify Oracle database storage administra-
tion. Database environments have become more and more complex, with large numbers
of (and larger) datafiles, storage area networks (SANs), and high-availability require-
ments. ASM is somewhat like a logical volume manager, allowing you to reduce the man-
agement of Oracle files into ASM disk groups.
ASM also provides redundancy configurations, rebalancing operations, and, when installed
on top of clusterware, the ability to share database-related files.
ASM stores files in
disk groups
, which are logical entities made up of one or more
physical disk drives. ASM is good for more than just storing database datafiles. In an ASM
instance, you can store database datafiles, online redo logs, archived redo logs, backup
files, and data-pump dumpfiles as well as change-tracking files and control files of one or
several Oracle databases.
ASM can also be used to store regular files through the support of Oracle database options
that provide the ability to mount an ASM disk group as a sharable file system. Oracle DBFS
or ACFS both provide these options and work in concert with the Oracle database. You can
create an Oracle DBFS or ACFS database, and after configuring the environment correctly,
you can then share out the space allocated to that database in the form of a OS file system.
While ASM does not require backing up (this occurs when you back up the databases
using ASM), it's still not a bad idea to back up metadata related to ASM. In the most severe
cases, it's possible that ASM metadata could get lost, and as a result, attributes related to
disk groups might end up being lost, or even the disk groups themselves. Obviously, you
can recreate the disk groups pretty easily, but since disk groups can have attributes custom-
ized, backing up the metadata and being able to restore it is a nice thing to have.
What are some of the things stored in the ASM metadata? How about the following:
■
The disks that belong to that disk group
■
The amount of space that is available in that disk group
■
All of the file names of the files in that disk group
■
The location of disk group data file extents
■
A log file that provides information about changing metadata blocks. This is much like
a redo log file
■
Oracle ADVM volume information
As you can see, ASM metadata is rich in information and it certainly needs to be pro-
tected. Let's see how we do that.
ASM Diskgroup Metadata Backups
To back up ASM diskgroup metadata, you will use the ASM command line administration
tool called
asmcmd
. To use
asmcmd
, you would set your environment for the ASM instance
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