Application Notes Device Mapper Multipath with Oracle ASM on Linux (5697-7806, April 2009)

On Linux, every path to the storage disk on SAN is represented by a device ﬁ le /dev/sd*. DM multipath

driver creates a pseudo device /dev/mapper/* which c an be used by the application for I/O. DM

multipath driver manages the I/Os sent to the disk and monitors the disk paths to balance the load across

all the available paths or to take corrective action in case of path failures.

In general, the pseudo devices under /dev/mapper are represented by the Universal Unique Identiﬁer

(UUID) of the corresponding logical devices. If the user_friendly_names parameter in the multipath

conﬁguration ﬁle is set to yes, then the devices u nder /dev/mapper are represented as mpath*.

The representation of the disks with user_friendly_names parameter set may differ (for example,

mpatha, mpath1) depending on the operating system distribution and version. The partition to these

disks may be represented as mpatha1, mpath1p1,andsoon.

NOTE:

Using fdisk command to create p artitions may fail to create multipath device for the pa rtition device. It

is recommended to use parted command to create partitions for the devic e.

For more information on device name aliases and multipath conﬁgurations, see the Linux Device Mapper

Multipath guide provided with the kit.

ConﬁguringOracleASMwithDMmultipath

ASM is a management tool speciﬁcally built to simplify the job of the DBA. It p rovides a simp le storage

management interface across all servers and storage platforms. ASM provides DBA the ﬂexibility to

manage a dynamic database environment with increased efﬁciency. Oracle ASM can stripe and mirror

your disks and allow disks to be added or removed while the database is under load. It also supports

direct and asynchronous I/O.

There are two different methods to conﬁgure ASM on Linux:

• ASM with ASMLib I/O: This method creates all Oracle database ﬁles on raw block devices managed

by ASM using ASMLib calls. Raw devices are not required with this method as ASMLib works with

block devices.

• ASM with Standard Linux I/O: This method creates all Oracle database ﬁles on raw character devices

managed by ASM using standard Linux I/O system calls. You will be required to create raw devices

for all disk partitions used by ASM.

We will examine the ASM with ASMLib I/O method here. ASMLib is a library add-on for use with the

Oracle ASM feature. Ensure that all the packages required to conﬁgure ASMLib are installed on the host.

ConﬁguringDMdevicesasASMdisks

To conﬁgure ASMLib, you must run a conﬁguration script to prepare the driver. Run the command

# /etc/init.d/oracleasm configure as superuser, and answer the prompts as shown in the

following example.

Example:

# /etc/init.d/oracleasm configure

Configuring the Oracle ASM library driver

This will configure the on-boot properties of the Oracle ASM library

driver. The following questions will determine whether the driver is

loaded on boot and what permissions it will have. The current values will

be shown in brackets (’[]’). Hitting <ENTER> without typing an answer will

keep that current value. Ctrl-C will abort.

Default user to own the driver interface []:oracle

Default group to own the driver interface []:dba

Start Oracle ASM library driver on boot (y/n) [n]:y