Managing AIX Devices used by Oracle Automatic Storage Management (ASM)

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2019-08-09

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IBM Oracle ICC Technical Notes

ibmoracle@us.ibm.com

Technical Notes

IBM Oracle International Competency Center (ICC)

August 03, 2012 email address: ibmoracle@us.ibm.com

Managing AIX Devices used by Oracle Automatic Storage Management (ASM)

Introduction

Traditionally, AIX storage devices were made available for use by assigning disk devices to Volume

Groups (VGs) and then defining Logical Volumes (LVs) in the VGs. When a disk is assigned to a VG,

the Logical Volume Manager (LVM) writes information to the disk and to the AIX Object Data Manager

(ODM). Information on the disk identifies that the disk was assigned to the LVM; other information in

the ODM identifies which VG the disk belongs to. System components other than the LVM can use the

same convention. For example, IBM’s General Parallel File System (GPFS) uses the same area of the

disk to identify disks assigned to it. AIX commands can use the identifying information on the disk or in

the ODM to help prevent a disk already in use from being reassigned to another use. The information can

also be used to display useful information to help identify disk usage. For example, the lspv command

will display the VG name of disks that are assigned to a VG.

When using Oracle ASM, which does its own disk management, the disk devices are typically assigned

directly to the Oracle application and are not managed by the LVM. The Oracle OCR and VOTING disks

are also commonly assigned directly to storage devices and are not managed by the LVM. In these cases,

the identifying information associated with disks that are managed by the LVM is not present. AIX has

special functionality to help manage these disks and to help prevent an AIX administrator from

inadvertently reassigning a disk already in use by Oracle and inadvertently corrupting the Oracle data.

Where possible, AIX commands that write to the LVM information block have special checking added to

check if the disk is already in used by Oracle to prevent these disks from being assigned to the LVM,

which would result in the Oracle data becoming corrupted. These commands, if checking is done, and the

AIX levels where checking was added is listed in Table 1.

AIX Command AIX 5.3 AIX 6.1

AIX 7.1

Description

mkvg TL07 or newer

All All Prevent reassigning disk used by Oracle

extendvg TL07 or newer

All All Prevent reassigning disk used by Oracle

chdev … -a pv=yes

chdev … -a pv=clear

- - - No checking

Table 1 – AIX commands which write control information on the disk and if and when checking for

Oracle disk signatures was added

IBM Oracle ICC Technical Notes

ibmoracle@us.ibm.com

Note in Table 1 that the chdev command with attribute pv=yes or pv=clear which will write to the VGDA

information block on the disk, does not have the checking for the Oracle disk signature. It is therefore

extremely important that this command is not used on a disk, which is already being used by Oracle, as it

could lead to corruption of the Oracle data. To help prevent this, additional functionality was added to

AIX.

AIX 6.1 and AIX 7.1 LVM commands contain new functionality that can be used to better manage AIX

devices used by Oracle. This new functionality includes commands to better identify shared disks across

multiple nodes, the ability to assign a meaningful name to a device, and a locking mechanism that the

system administrator can use when the disk is assigned to Oracle to help prevent the accidental reuse of a

disk at a later time. This new functionality is listed in Table 2, along with the minimum AIX level

providing that functionality.

The use of each of the commands in Table 2 is described in the sections below.

AIX lkdev Command:

The AIX lkdev command should be used by the system administrator when a disk is assigned to Oracle to

lock the disk device to prevent the device from inadvertently being altered by a system administrator at a

later time. The lkdev command locks the specified device so that any attempt to modify the device

attributes (chdev, chpath) or remove the device or one of its paths (rmdev, rmpath) will be denied. This is

intended to get the attention of the administrator and warn that the device is already being used. The “-d”

option of the lkdev command can be used to remove the lock if the disk is no long being used by Oracle.

The lspv command with the “-u” option indicates if the disk device is locked. The example section of this

paper shows how to use lkdev and the related lspv output.

AIX rendev Command:

The AIX rendev command can be used to assign meaningful names to disks used by the Oracle Database,

Cluster Ready Services (CRS) and ASM. This is useful in identifying disk usage because there is no

indication in output from AIX disk commands indicating that a disk is being used by Oracle. For

example, the lsps command does not indicate the disk is used by Oracle. The command can be used to

assign a meaningful name to the Oracle CRS OCR and VOTING disks, whether they are accessed as raw

devices (prior to 11gR2) or through the ASM (11gR2 and later).

AIX

Command

AIX

5.3

AIX

6.1

AIX

7.1

Description

lspv NA TL07 TL01 New AIX lspv command option “-u” provides additional

identification and state information

lkdev NA TL07 TL01 New command can lock a device so that any attempt to

modify the device characteristics will fail.

rendev NA TL06 TL00 New command to rename device.

Table 2 – New AIX Commands Useful for Managing AIX Devices Used by Oracle ASM

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