Tuning the Storage Subsystem - Expert Oracle RAC Performance Diagnostics and Tuning - page 368

ASM
Instance

ASM
Instance

Database Database

Tablespace Tablespace

Oracle Managed Files Oracle Managed Files

Disk Group Disk Group

Logical Volumes

Physical Volume

Disk spindles Disk spindles

Configuration type A Configuration type B

Figure 12-9. ASM disk structure

ASM Clustered File System
The ACFS architecture introduces a new ASM file type, known as a dynamic volume. A dynamic volume is essentially
an ASM file that can be presented as a volume to a file system rather than as a data file to the Oracle database. The
ASM Dynamic Volume Manager (ADVM), along with the associated device driver, provides the interface between
dynamic volumes and the ACFS. You can even run other file systems, such as ext3, over an ASM dynamic volume.
The ADVM is an enabler of ACFS. It provides volume-management services and a standard disk device driver
interface, thus enabling ACFS to utilize the space allocated to an ASM dynamic volume inside an ASM disk group. An
ASM dynamic volume is a new type of ASM file that can be used to house a file system. Like other ASM files, an ASM
volume file must be wholly contained within a diskgroup, and there can be many volume files in one diskgroup.
ASM dynamic volumes are created using SQL or by means of the ASMCMD command-line tool or the ASMCA
graphical management tool. After a volume is created, it needs to be enabled in order to generate an operating system
device node under /dev/asm . An ACFS is created over the ASM volume device. Alternatively, an ASM volume device
can be used to support other file systems, such as ext3.
An ADVM driver maps I/O requests against an ASM volume device to the underlying dynamic volume file
contained inside an ASM diskgroup.