Shared Application File System in R12 and 11i

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E-Business suites (EBS) 11i and R12 both support the sharing of the Applications Tier File System. Sharing a file system in EBS involves sharing a volume between 2 or more physical servers. In a shared Application Tier File System (ATFS) implementation, the application services can be configured to run (utilize CPU and memory) on any server sharing the ATFS simply by changing some context file variables via OAM, running Autoconfig and restarting the services. This process is detailed in the following notes:

R12: Note.384248.1: Sharing the Application Tier File System in Oracle E-Business Suite Release 12
11i:   Note.233428.1: Sharing the Application Tier File System in Oracle Applications 11i

Some key concepts of sharing ATFS:

• Each server sharing the ATFS will have its own context file
• Certain context file variables dictate which application services start and run on which server(s)
• Certain context file variables dictate how AD Utilities will behave on each server

The Unified Applications Tier File System (UATFS)

The term "Unified Applications Tier File System" (UATFS) came along with R12 as a new feature. Oracle Development decided it would be beneficial to always install all the files needed on every server in a given R12 installation, even if the server was only to host some of the Application services. Even though this term was coined for an R12 feature, it still applies to some 11i file systems. A Unified Applications File System essentially means that the file system contains all the files required to support all 4 base service groups in E-Business Suite:

• Web
• Forms
• Admin (Not a true process or service as the other 3 are. The "admin" component dictates which server administers the application database objects and therefore has the needed files for that task.)
• Concurrent Processing (Reports)

Again, all versions of R12 are always installed with UATFS as delivered by Rapid Install. However in 11i only single node-installations are unified at install time. In 11i in order to achieve a unified file system from a multi-node installation, a merge of the file systems must be performed. This is the only supported manner in which to achieve a unified file system from an installation which was originally multi-node. APPL_TOP Merging in 11i is accomplished by Note 233428.1, Section 4, "Merging existing APPL_TOPs into a single APPL_TOP". Because R12 is always unified there is not an APPL_TOP merge process in R12.

Some Non-Typical Scenarios for Shared File Systems in 11i

In 11i it is also possible to share an ATFS even if the file system is not unified or complete; i.e., it only supports 1, 2 or 3 of the 4 core services. For example 11i can have an ATFS which only has the files for Forms and Web. That ATFS can then be shared with another server for Forms / Web services only. The other core services, Admin and Concurrent would then have its own ATFS on another server or servers. This would be done for some advanced topology configurations like load-balancing or perhaps a standby Web / Forms server and would minimize the footprint of the ATFS. Because the ATFS in this example is not unified, the ATFS of the Forms/Web servers could never host the Concurrent Processing or Admin services without first being merged with an ATFS which has the necessary Concurrent Processing and Admin files. So while in 11i it is possible to share a non-unified ATFS, it would not be a typical configuration. A typical configuration is sharing 1 unified ATFS for amongst multiple servers. The advantages of this non-typical example would be:

• Smaller Footprint for the ATFS on each volume/disk (however the overall combined footprint would be larger)
• Better performance from the shared volume/disk, as there are 2 instead of 1

The disadvantages would be:

• Must maintain multiple ATFS's
• Patches have to be applied multiple times 
• Cloning is more difficult as 2 ATFS's must be cloned

For disk performance reasons, you could implement a similar strategy in R12, for example sharing 2 volumes (VOL1, VOL2) amongst 4 servers: 2 web/forms servers accessing only VOL1 and the 2 CCM/Admin servers accessing only VOL2. Those 2 disks would each have a unified ATFS in R12, where the same configuration in 11i the file systems could be partial or unified.

For more information please refer :

Explanation of Context Variables for Shared Application File System in R12 and 11i [ID 1070152.1]

References
NOTE:233428.1 - Sharing the Application Tier File System in Oracle Applications Release 11i
NOTE:384248.1 - Sharing The Application Tier File System in Oracle E-Business Suite Release 12
NOTE:406558.1 - Configuring Applications Node Services in Oracle E-Business Suite Release 12
NOTE:415385.1 - On a R12 Multi-Node Install -- Why do all Middle Tiers run all Services?