Oracle ASMLib

Oracle ASMLib

 

Oracle ASMLib is an optional software component that can be used in configurations utilizing Oracle ASM on Linux. ASMLib allows an Oracle Database using ASM more efficient and capable access to the disk groups it is using.

 

Purpose of Oracle ASMLib

    -  Persistent Device Naming

• Linux does not guarantee persistent device naming w/o further mechanisms 
•  Note: ASM would be able to find its disks by scanning the device header, so a changed device name wouldn‘t be a problem. But you would still have to configure the correct ownership and permissions for the device file for ASM to be able to work with this device

    -  Correct ownership and permissions for the ASM devices

    -  Before Oracle 10gR2 the limited number of raw devices supported by the kernel could become a problem (Kernel 2.4: 256 devices, Kernel 2.6: 8192 devices); but starting with 10gR2 Oracle ASM is able to use block devices directly (w/o raw emulation)

    -  With ASMLib the disks are correctly released after having dropped a disk group (with block devices you must clean them (with dd))

Availability of Oracle ASMLib

 

Oracle ASMLib is only available for Linux; as a kernel module is needed only the supported Linux distributions, the required RPM packages are downloadable from OTN.

 

For RHEL6, Oracle will only provide ASMLib software and updates when configured with a kernel distributed by Oracle. Oracle will not provide ASMLib packages for kernels distributed by Red Hat as part of RHEL6. ASMLib updates will be delivered via Unbreakable Linux Network(ULN) which is available to customers with Oracle Linux support.

 

Installation and configuration

 

First we have to install the needed rpms, The three RPM packages are installing with the standard rpm command:

·         oracleasm-support-xxxxxxx.rpm: Utilities used to get the ASM driver up and running

·         oracleasmlib- xxxxxxx.rpm : Actual ASM library

·         oracleasm- xxxxxxx.rpm : Kernel driver for the ASM library

Note: When using the “Unbreakable Enterprise Kernel” from Oracle, the kernel driver is already included in the Kernel.

 

Usage of oracleasm command:

 

# oracleasm -h

Usage: oracleasm [--exec-path=<exec_path>] <command> [ <args> ]

oracleasm --exec-path

oracleasm -h

oracleasm –V

The basic oracleasm commands are:

configure     Configure the Oracle Linux ASMLib driver

init          Load and initialize the ASMLib driver

exit          Stop the ASMLib driver

scandisks     Scan the system for Oracle ASMLib disks

status        Display the status of the Oracle ASMLib driver

listdisks     List known Oracle ASMLib disks

querydisk     Determine if a disk belongs to Oracle ASMlib

createdisk    Allocate a device for Oracle ASMLib use

deletedisk    Return a device to the operating system

renamedisk    Change the label of an Oracle ASMlib disk

update-driver Download the latest ASMLib driver

Initial configuration

The initial configuration is being started with the command “oracleasm configure”:

# oracleasm configure –i

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

Scan for Oracle ASM disks on boot (y/n) [y]: y

Writing Oracle ASM library driver configuration: done

Usually is the user “oracle” the owner of the driver interface, but in case of privilege separation the owner can be the grid user; the same applies to the group (here “dba”). In most configurations it makes sense to have the driver interface automatically started at system boot and also to scan for ASM(Lib) disk devices at startup.

Oracleasm processes need to be started manually if no reboot takes place after the installation:

# oracleasm init

Creating /dev/oracleasm mount point: /dev/oracleasm

Loading module "oracleasm": oracleasm

Mounting ASMlib driver filesystem: /dev/oracleasm

Disk creation (labelling), the device needs to be partitioned :

# oracleasm createdisk DATA1 /dev/sdc1

Writing disk header: done

Instantiating disk: done

The device is now configured and can be listed:

# oracleasm listdisks

DATA1

In a RAC you would have to scan for the devices on the other nodes:

# oracleasm scandisks

Reloading disk partitions: done

Cleaning any stale ASM disks...

Scanning system for ASM disks...

# oracleasm listdisks

DATA1

You can check if a disk is in use with ASM(Lib):

# oracleasm querydisk /dev/sdc1

Device "/dev/sdc1" is marked an ASM disk with the label "DATA1"