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Readers,
My
name is Franz Devantier, creator of this blog. I am an Oracle Certified
Professional (OCP DBA 11g) Security DBA.
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some of the undocumented, and not so well known tasks.
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Contact: devantierf@gmail.com
Oracle Grid
Infrastructure – Part 3
General Steps for
Configuring Oracle Automatic Storage Management
Step 1:
Identifying Storage Requirements for Oracle Automatic Storage Management
You need to determine the
number of devices and the amount of free disk space that you require, so that
you can determine the storage requirements for you ASM instance.
=> You need to decide
whether you are going to use the ASM instance for your database files, or for
your recovery files, or for both. You
can for example store your database files in ASM, and your recovery files in
file systems. If you have for example
enabled automated backups, then they can be configured for an available shared
file system, or use ASM for recovery file storage. At this stage it will be a good idea to
document the reasons for the choices that you make.
If you are going to use ASM
for your backup files, then during the Oracle database installation, you
specify an Oracle ASM disk group for the fast recovery area.
When you create a database
during the database installation you have two different options.
=> You can run Automatic
Storage Management Configuration Assistant (ASMCA) in interactive mode to create
and configure your disk groups. When you
run Database Configuration Assistant (DBCA), and you select the Advanced
installation type, then you will be able to select the disk groups that you
created using ASMCA earlier on. This
will allow you to select the disk groups that you created with ASMCA for the
database files and the recovery files.
Ideally you should use separate disk groups for the database files and
the recovery files.
=>
You can run ASMCA in non-interactive mode, which will result in using the same
ASM disk groups for both data files and recovery files. During the database installation, you choose
the Typicl installation type, and you will have to select the same disk group
for both database files and recovery files.
=>
The next thing to do is to choose the Oracle ASM redundancy level that you want
to use for each Oracle ASM disk group, that you want to create. This decision will affect the way that ASM
mirrors the files in the disk group, and also determines the number of disks
and the amount of disk space that you will require.
External Redundancy
This
option does not allow ASM to mirror the contents of the disk group. Oracle recommends that you only select this
redundancy level when the disk group contains devices, such as RAID devices,
that provide their own data protection.
You can also choose this redundancy level when the database does not
require uninterrupted access to data.
Normal Redundancy
Oracle
ASSM uses two-way mirroring for data files and three way mirroring for control
files. This provides optimal performance
and reliability in a normal redundancy disk group. Also with Normal redundancy you can choose
the mirroring characteristics for individual files in a disk group. You can go with the two way mirroring or
decide to use no mirroring.
A
normal Redundancy disk group will require a minimum of two failure groups, or
two disk devices, in order to enable the two way mirroring. The effective disk space in a normal
redundancy disk group is half the sum of the disk space of all its devices.
Oracle
recommends Normal redundancy disk groups for most types of installations.
High Redundancy
The contents of the disk
groups are three-way mirrored by default.
In order to create a disk group with high redundancy, you need to
specify at least three failure groups, which are mapped to a minimum of three
devices.
High-redundancy disk groups
do provide a high level of data protection, which needs to be balanced against
the cost of the additional storage devices needed.
=> You need to determine
the total amount of disk space that you will require for the database files and
the recovery files. If there is an
existing ASM instance, then you can use it.
It is [possible to add disks to an existing disk group during the database
installation. You can put the
information in table format, to help you to come up with the final numbers.
|
Redundancy
|
Minimal Disks
|
Data files
|
Recovery files
|
Both file type
|
|
External
|
1
|
2 GB
|
6 GB
|
8 GB
|
|
Normal
|
2
|
4 GB
|
12 GB
|
16 GB
|
|
High
|
3
|
6 GB
|
18 GB
|
24 GB
|
You can see that in this
theoretical scenario, the Normal redundancy seems to make the most sense. Also you may decide to keep your recovery
files in external redundancy disk groups, or in normal file systems. For example if you had your data files in Normal
redundancy 4GB, and your recovery files in External redundancy 6GB, then you
have a total of 10GB. If you had them
all in Normal redundancy, then you would be looking at a total of 16 GB.
=>
You can also optionally identify failure groups for the Oracle ASM disk group
devices. For example if you are using
normal redundancy, and there are two disk devices in the disk group. If both devices are connected to the same
SCSI controller, then if the controller fails, then the disk group becomes
unavailable. So the SCSI controller
becomes the single point of failure rather than the disk. To avoid such a failure, you can have two
SCSI controllers, and define the disks of a disk group to be physically connected
to the two SCSI controllers. Then if there
is a SCSI controller failure, you have avoided a disk group failure, and your
configuration is now able to tolerate the failure of one of the SCSI
controllers.
=>
If you are sure that a suitable disk group is not available, then you can
install or identify disk devices to add to a new disk group.
.
Make sure that the disk devices are owned by the user performing the Grid
installation.
.
All the devices in an Oracle ASM disk group must be the same size and have the
same performance specifications.
.
Do not specify multiple partitions on a single physical disk, as a disk group
device. Oracle ASM expects each disk
group device to be on a separate physical disk.
.
It is possible to specify a logical volume as a device in an Oracle ASM disk
group. Oracle recommends that you don’t
do this, because it adds a layer of unnecessary complexity with Oracle ASM.
.
Oracle recommends that if you do a logical volume manager, then you should use
the logical volume manager to represent a single logical unit number(LUN)
without striping or mirroring. This will
minimize the effect of the additional storage layer on the storage performance.
Step 2: Creating
DAS or SAN Disk Partitions for Oracle Automatic Storage Management
You can use any physical disk
for Oracle ASM, if it is partitioned. A
DAS or SAN disk must have a partition table in order to be used in Oracle
ASM. Oracle recommends creating just one
partition on each disk.
Step 3:
Configuring Disks for Oracle Automatic Storage Management
In order to simplify the
configuration and management of the disk devices to use with Oracle ASM, Oracle
provides an ASM Library Driver. Once you
have configured a disk to ASM, it is known as a candidate disk.
If you are going to use ASM
for database storage, then Oracle recommends that you install the Automatic
Storage Management Library (ASMLIB) driver, as well as the associated
utilities. ASMLIB and the associated
utilities will then be used to configure the devices to be included in an
ORACLE ASM disk group. When you
configure disks using the ASMLIB, then you should change the default discovery
string to “ORCL:*” or empty “”. When it
is set like this, then the installer discovers these disks.
Franz
Devantier,
Need
a database health check?
devantierf@gmail.com
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