One of the new features in Oracle 11g Release 2 is Automatic Storage Management Cluster File System. This file system provides concurrent access from multiple (clustered) nodes.
ACFS is provided through the Automatic Storage Management Dynamic Volume Manager. In order to have a file system, one needs a volume (be it physical or logical) to put it on. Oracle has developed a Dynamic Volume Manager (ADVM) that can provide these volumes from ASM Diskgroups. You can use ADVM to create volumes that are replicated within the ASM diskgroup mechanism – by means of normal or high redundancy. Multiple volumes can reside on one diskgroup. The ADVM provides a device driver interface to the ACFS client.
Due to the mirroring features of ASM, it is possible to have a mirrored file system (even across a stretched cluster, when your storage infrastructure allows for such an architecture) that will leverage the features of ASM to provide consistency over hardware failure and ASM instance crashes.
You can use the file systems provided through ADVM not only for database files, but also for regular files such as executables and log files. During creation of the file system you have the choice to designate the file system for Oracle Home functionality. By choosing this option, the file system is registered in the Cluster Registry as a managed resource, giving Oracle the opportunity to layer dependencies on this file system for the use of Oracle Homes.
Because of the fact that Oracle ADVM Volumes are technically spoken ASM files located on ASM Disk groups, and the fact that the Dynamic Volumes do not use the traditional device partitioning, it enables Oracle to extend some of the ASM features to the ASM Clustered File Systems, which are created inside these ADVM Volumes, such as dynamic resizing or dynamically adding volumes. This makes ADVM and ACFS a far more flexible solution than traditional physical devices.
Important Note: Oracle ADVM supports all storage solutions supported for Oracle ASM with the exception of NFS and Exadata storage. That will have to wait for some time still…
The above picture shows the User Interface, provided through the ASM Configuration Assistant (asmca), to create file systems inside ASM using the ADVM.