ASMFD (ASM Filter Driver) Support on OS Platforms (Certification Matrix). (文档 ID 2034681.1)

1) Starting with Oracle Grid Infrastructure 12C Release 1 (12.1.0.2), Oracle ASM Filter Driver (Oracle ASMFD) is installed with an Oracle Grid Infrastructure installation.

2) Oracle Automatic Storage Management Filter Driver (Oracle ASMFD) 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 ASMFD, assuming the partition table is left untouched by the user.

3) Oracle ASMFD simplifies the configuration and management of disk devices by eliminating the need to rebind disk devices used with Oracle ASM each time the system is restarted.

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

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

• Reject non-Oracle I/Os.

 As a manager of Oracle storage, ASM is exposed to the capabilities of the Operating System (OS) when it comes to dealing with storage devices. In particular, non-Oracle commands have the ability to overwrite the contents of ASM disks which may lead to unrecoverable data loss. ASMFD only allows writes using an Oracle-specific interface and prevents non-Oracle applications from writing to ASM disks. This protects ASM from accidental corruption. 

• Reduce OS resource usage.

 An ASM instance contains numerous processes, or threads on Windows. Without ASMFD, 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. ASMFD 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 ASMFD, the required number of open file descriptors is drastically reduced. 

• Enable device name persistence.

 ASMFD do not require additional configuration to ensure device name persistence by using udev rules or third-party storage drivers. 

• Faster node recovery.

With the current implementation of Oracle Clusterware, init.d scripts panic the node in situations when Cluster Synchronization Services (CSS) is not functioning correctly. Using this mechanism, nodes are fenced to ensure the integrity of the rest of the cluster. While effective, this solution is costly because of the time required to reboot the node and restart all the required processes. ASMFD allows Oracle Clusterware to perform node level fencing without a reboot. So with ASMFD, it is possible to achieve the same result by restarting the Oracle software stack instead of rebooting the entire node. This process is just as effective, but far quicker.

6) For additional information about ASMFD overview, characteristics & features please look at the following document (click on the picture or link below):