As per my working experience..
>> fs1 and fs2 works as dual system at a particulary time, like patching.
While patching, run file system (fs1) run as usual and patch will be applied in patch file system till finalize phase.
fs1 - run file system
fs2 - patch file system.
But after cutover phase, it will be changed as follows -
fs1 - patch file system
fs2 - run file system
Now, ebs mainly running on fs2.
This is the way, dual file system works.
For more information, and to be expert and more, find all documents from below link,
a. For Architecture: https://docs.oracle.com/cd/E26401_01/doc.122/e22949/T120505T120508.htm
b. For Patching Phase Details: https://docs.oracle.com/cd/E26401_01/doc.122/e22954/toc.htm
2. Yes.. application tier will work without patch file system. For me, patch file system is not working but run file system is okay and running file.
Because of that we are unable to apply patch. So, we are trying to recover patch file system.
Hope, it will help you to get overview for dual file system.
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