Datasheet

Working with the ASM Instance

Another thing to consider when determining how to conﬁgure the ASM_DISKSTRING param-

eter is performance. Leaving this parameter set to

NULL, and thus taking the Oracle default,

will often be sufﬁcient. However, if you set

ASM_DISKSTRING using a more restrictive set of

parameters, you may ﬁnd that discovery of disks will be faster. For example, using the default

Linux setting of

/dev/raw/* will result in ASM scanning the entire /dev/raw ﬁle system

structure (it does not search subfolders). If you have a large number of devices in this struc-

ture, this may take some time. If, however, your disk devices in this structure are all preﬁxed

with the word raw (raw1, raw2, raw3, and so on), then setting the

ASM_DISKSTRING to /dev/

raw/raw*

could reduce the time it take ASM to perform discovery and improve performance

of the startup of the ASM instance.

Something you will see common to all

ASM_DISKSTRING parameters is the use of the

asterisk. The asterisk is required when deﬁning the

ASM_DISKSTRING parameter. Here are

some examples of setting the

ASM_DISKSTRING parameter. In this ﬁrst example, ASM will

look for disks in devices when we create disk groups:

Alter system set ASM_DISKSTRING=’/devices/*‘;

In the next example, we are pointing ASM_DISKSTRING to ORACLE_HOME/disks:

Alter system set ASM_DISKSTRING=’?/disks/*‘;

In this example, we are pointing ASM_DISKSTRING to two different locations:

Alter system set ASM_DISKSTRING=’?/disks/d1/*,?/disks/d21/*‘;

We could also use some adjunctive regular expressionish–type extensions and perform

the allocation this way:

Alter system set ASM_DISKSTRING=’?/disks/d[12]/*‘;

ASM Disk Discovery on Instance Start

When the ASM instance is started, it will use the paths listed in the ASM_DISKSTRING param-

eter and discover the disks that are available. These disks can then be added to ASM disk

groups that we will discuss in the next section. Once discovery is complete and the ASM

instance is open, you can review the disks discovered by looking at the

V$ASM_DISK view, as

shown in this example:

column path format a20

set lines 132

set pages 50

select path, group_number group_#, disk_number disk_#, mount_status,

header_status, state, total_mb, free_mb

from v$asm_disk

order by group_number;

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