ASM : Lesson -2 How to prepare the ASM disks

ASM Disks
The first task in building the ASM infrastructure is to discover and associate (adding) ASM disks under ASM
management. This step is best done with the coordination of Storage and Systems administrators. The
Storage administrator will identify a set of disks and create the appropriate LUNs from the storage array
and finally present them to the host. The ASM disk could be any of these1) Raw disk partition—A raw partition can be the entire disk drive or a section of a disk drive.
However, the ASM disk cannot be in a partition that includes the partition table because the
partition table can be overwritten.2) Logical unit numbers (LUNs)—Using hardware RAID functionality to create LUNs is a recommended
approach. Storage hardware RAID 0+1 or RAID5, and other RAID configurations, can be provided to
ASM as ASM disks.3) Raw logical volumes (LVM)—LVMs are supported in less complicated configurations where an LVM
is mapped to a LUN, or an LVM uses disks or raw partitions. LVM configurations are not recommended
by Oracle because they create a duplication of functionality. Oracle also does not recommended
using LVMs for mirroring because ASM already provides mirroring.

Procedure to prepare the disks for ASM

1) Identify or create the storage devices for ASM by identifying all of the storage resource
device names that you can use to create an ASM disk group.

2) Change the ownership and the permissions on storage device resources to oracle:dba or oracle:oinstall. It all depends on your configuration

3) On solaris, the disk which are presented on ASM should be on disk partition 6  and it should be formatted on cylinder 1. Similarly other OS have different formmating criteria

3) After you have configured ASM, ensure that disk discovery has been configured correctly by setting
the ASM_DISKSTRING initialization parameter.

Disk Header status

Disks have various header statuses that reflect its membership state with a diskgroup.Disk header status could be find using the query
select path,header_status from v$asm_disk;

Former – This state declares that the disk was formerly part of a diskgroup
Candidate – When a disk is in this state, it indicates that it is available to be added to a diskgroup.
Member – This state indicates that a disk is already part of a diskgroup.
Provisioned – This state is similar to candidate, in that its available to diskgroups.