Shared appltop setup in Oracle E-Business Suite (EBS) is very common nowadays, for obvious reasons. It cuts down the patching downtime enormously on large multi middle tier environments, as we just have apply the patches on only one node instead of all nodes. Any apps patch or apps techstack patch need to be applied only once, Thus Downtime window for production multi middle tier setups with shared Appl_top is significantly less. In the current era of Global Single Instance Architecture any investment in cutting down downtime windows is a very good choice.
One of the requirement for Shared Appl_top setup is to have apps filesystem shared between all the nodes. This requires a Single LUN mounted to all nodes with cluster filesystem on it. Another alternative to cluster filesystem is NFS mount point from a NAS device.
NFS mount point from a NAS device is the most recommended for Apps Filesystem, as this setup doesn’t have any overhead or issues that Cluster filesystems have. NFS doesnt have any fencing issues unlike Cluster filesystems. Yes, it’s slower in IO throughput, but Apps Filesystem doesn’t do a kot of IO. NFS IO performance is more than adequate for Shared Appl_top Filesystem.
Customers who don’t have NAS based storage around in their data centers, traditionally SAN with FC or iSCSI, have to use Cluster Filesystems like Redhat GFS, IBM GPFS or Veritas VxFS. I have seen a lot of customers chose Redhat GFS for their systems, but my experience with Shared Appl_top on Redhat GFS is not good. GFS has difficulties in handling directories that have lot of small files like Concurrent Manager log and output directories. Simple ls command on this directory hangs forever and seems to effect other nodes response time as well. Note that Oracle doesn’t normally recommend or certify any of the above mentioned Cluster filesystems with EBS. But in recent years, Oracle caved in to customer pressure and certified OCFS2 cluster filesystem with EBS R12 shared appltop.
In initial years of this certification, I had second thoughts about using this for Shared Appl_top. OCFS did not really have a good reputation with Oracle RAC which seems to have affected its credibility in this area. But latest versions of OCFS improved a lot and OCFS2 1.6 performed really well in my recent tests with Oracle EBS R12. I highly recommend OCFS2 in addition to NFS for Oracle EBS Shared Appl_top. Whatever you choose, just make sure to mount them with noatime option for better performance.
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