Introducing Oracle AFD

Before Oracle grid infrastructure 12c, the only method to access ASM disks was ASLIB. With the start of GI 12c (12.1.0.2), Oracle Introduced Oracle AFD (ASM Filter Driver). Oracle AFD has been come to cover weaknesses of the ASMLIB.

You could find some of the benefits using AFD (ASM Filter Driver) as below:

• Rejection of non-Oracle I/Os.

Oracle Automatic Storage Management Filter Driver (Oracle AFD) rejects write I/O requests that are not issued by Oracle software. This filter helps to prevent users with administrative privileges from inadvertently overwriting Oracle ASM disks, thus preventing corruption in Oracle ASM disks and files within the disk group. For disk partitions, the area protected is the area on the disk managed by Oracle AFD, assuming the partition table is left untouched by the user.

• AFD is a superset of ASMLIB

AFD is a superset of ASMLIB; therefore it includes base-ASMLIB features (permissions persistence & sharing open handles).

• Oracle AFD is a kernel module

The Oracle ASM filter driver (AFD) is a kernel module that resides in the I/O path of the Oracle ASM disks. Logically, AFD provides an interface between Oracle binaries and the underlying operating environment which includes the storage hardware interfaces.

• Reduction of OS resource usage

An ASM instance contains numerous processes or threads on Windows. Without AFD, each process that is I/O capable needs to have its own dedicated open file descriptor for each disk. When a database has thousands of processes accessing hundreds of disks, there is an explosion of file descriptors leading to considerable OS resource consumption. AFD exposes a portal device that can be used for all I/O on a particular host. The same portal device can be shared by all the processes associated with multiple database instances. The result is that using AFD, the required number of open file descriptors is drastically reduced.

• Limitation of Oracle AFD

1. The AFD is available on Linux from 12.1.0.2 onward
2. The AFD is available on Solaris from 12.2.0.1 onward
3. Another OS is not supported yet
4. AFD and ASMLIB are mutually exclusive

You could find more information about Oracle AFD in MOS.

• Examples:

1. Configuring Oracle AFD After Installation
2. Migrating to Oracle ASMLIB From AFD