Support of Oracle RAC ASM with SGeRAC, January 2008

HP Availability Clusters Solutions Lab 1/25/2008 Page 15

1. Export the volume group across the SGeRAC cluster and mark it as shared, as specified by

SGeRAC documentation.

Assign the right set of ownerships and access rights to the raw logical

volumes on each node as required by Oracle (oracle:dba and 0660, respectively).

We can now use the raw logical volume device names as disk group members when configuring

ASM disk groups using the Oracle database management utilities. There are a number of ways of

doing this described in Oracle ASM documentation, including the dbca database creation wizard as

well as sqlplus.

The same command sequence, with some modifications, can be used for adding new disks to an

already existing volume group that is being used by ASM to store one or more RAC databases. If the

database(s) should be up and running during the operation, we use the Single Node Online volume

Reconfiguration (SNOR) feature of SLVM.

Step 1 of the above sequence is modified as follows:

• First, deactivate the volume group vgora_asm on all nodes but one, say node A. This

requires prior shutdown of the database(s) using ASM-managed storage and ASM itself, on

all nodes but node A. See the section to understand why it is not adequate to shut down

only the database(s) using the volume group to be reconfigured, and why we must shut

down ASM itself and therefore all database(s) using ASM-managed storage, on all nodes

but node A.

• Next, on node A, switch the volume group to exclusive mode, using SNOR.

• Initialize the disks to be added with pvcreate, and then extend the volume group with

vgextend.

Step 2 remains the same. Logical volumes are prepared for the new disks in the same way.

In step 3, switch the volume group back to shared mode, using SNOR, and export the VG across the

cluster, ensuring that the right ownership and access rights are assigned to the raw logical volumes.

Activate the volume group, and restart ASM and the database(s) using ASM-managed storage on all

nodes (they are already active on node A).

ASM over Raw disk

As mentioned above, a new I/O infrastructure that enables the native built-in multipathing

functionality is included in HP-UX 11i v3. This feature offers users a continuous I/O access to a LUN

or disk if any of the paths fails. This newly added functionality enables SGeRAC (11.17.01 or later)

to support ASM on raw disks/disk array LUs. In HP-UX 11i v3, new DSF is introduced. SGeRAC will

support the DSF format that ASM support with the restriction that native multipathing feature is

enabled.

The advantages for “ASM-over-raw” are as follow:

• There is a small performance improvement from one less layer of volume management.

• Online disk management (adding disks, deleting disks) is supported with ASM-over-raw.

The disadvantages for “ASM-over-raw” are as follow:

• Might not see the HP-UX devices (raw disks/disk array LUs) used for disk group members

as the same names on all nodes.

• There is no protection to prevent the raw disks from being incorporated into VxVM

volume/disk groups.