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Limitations of ASM for RAC Database Use

Oracle RAC Cluster Tips by Burleson Consulting

This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters.  To get immediate access to the code depot of working RAC scripts, buy it directly from the publisher and save more than 30%.

No ASM Support for:

* External Tables (yet 10g offers much improved External Table Support)

* Transportable Tablespaces capability is somewhat restrictive. It can be used with RMAN only.

*  Reports, Export/Import output cannot go onto ASM resources.

* SQL*Loader Files can not be located in ASM

* Oracle Home Files ? Oracle need either local file system or fully functional cluster file system

Supported File Types

The following table shows the types of files ASM Supports. The default template specifications assign fixed attributes like level of redundancy and level of striping.




Control Files



Data Files



Redo Log Files



Archived Log Files



Trace Files



Database Temporary Files



Data File Backup pieces



Archive Log Backup Pieces



Parameter Files



Operating System Files



Alter Log Files



Flashback Logs



Data Punp Sets



Table 5.4: The types of files ASM Supports


For the Linux platform, Oracle provides ASMLib which is a library add-on for the ASM. ASMLib is the kernel driver for generic Linux implementation. ASMLib allows an Oracle Database using ASM more efficient and capable access to the disk groups it is using.

At the time of the writing of this chapter, the Oracle ASMLib 1.0.0 was available for free download at This library is available for the following Linux flavors.

* Red Hat Advanced Server 2.1 (x86)

* Red Hat Enterprise Linux 3 AS

* United Linux 1.0 SP3 / SLES 8 SP3 (x86)

* United Linux 1.0 SP3 / SLES 8 SP3 (ia64)

* United Linux 1.0 SP3 / SLES 8 SP3 (amd64)

The ASM Library Files are available as rpm(s). Install the packages by using the following command:

rpm -Uvh oracleasm-support-1.0.0-1.i386.rpm \

     oracleasm-lib-1.0.0-1.i386.rpm \


Once the ASMLib software is installed, the ASM driver needs to be loaded, and the driver filesystem needs to be mounted. This is achieved by the initialization script, /etc/init.d/oracleasm.

By root privilege, execute the /etc/init.d/oracleasm script with the configure option. It will ask for the user and group that default to owning the ASM driver access point. If the database was running as the oracle user and the dba group, the output would look like this:

[root@ca-test1 /]# /etc/init.d/oracleasm configure

Configuration of CFS or Raw Devices

In the previous sections, the creation and usage of the ASM instance resources was examined. In this section, how to configure raw devices and Cluster File Systems will be covered. For studying the creation of raw partitions, a typical Linux environment and raw device configuration will be used. For CFS, three products will be examined; PolyServe Matrix Server; OCFS; and Veritas CFS

Once the decision has been made to use either raw devices or cluster file system files, a plan needs to be made for setting up the necessary storage volumes and file systems. The RAC system requires a minimum set of files/raw devices for creating default tablespaces and setting the redo log files etc.

If the DBCA utility will be used to create the initial database, there are certain requirements that need to be met concerning the default schemas. Raw devices need to be provided or file systems to store them. Then the user-defined or business application-related schemas and tablespaces are created.

In the case of UNIX and Linux-oriented cluster platforms, most of the vendors provide some kind of volume manager or tool, which helps to create volumes of manageable size and layout at the host level. These volumes can be used by the RAC database as raw partitions. Optionally, when using the cluster file system, the file system can be made and mounted. When planning to use the volumes as the raw partitions, it may be necessary to plan and pre-create a large number of partitions with appropriate sizes. Figure 5.14 shows the relationship between the storage volumes and how they are presented for the use of the RAC database.

A LUN is the concept of the usable disk. LUN stands for Logical Unit Number. It is a physical disk, as seen by the node or host. They are also called RAID logical drives. Once they are introduced into a disk group at the volume manager level, they become the basis for logical volume creation. Volumes are usable pieces carved out of the storage pool. When they are used by the database application, they are the raw partitions. When a file system is created on the volumes, they become mountable at the operating system level. Figure 5.14 shows the connection between the storage structures.

Figure 5.14:  Storage Volume Relations

In the case of a Windows platform, the Windows disk manager provides a facility to create raw partitions. When using the OCFS (Oracle Cluster File System) module, Veritas CFS or PolyServe, appropriate cluster file system mount points can be created.


This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters, Rampant TechPress, by Mike Ault and Madhu Tumma.

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


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