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In eXo Platform, the persistence mostly relies on JCR, which is a middleware between the eXo Platform applications (including the Portal) and the database. Hence, this component must be configured to work in the cluster mode.
The embedded JCR server requires a portion of its state to be shared on a file system shared among the cluster nodes:
The values storage.
The index (in case of shared index usage).
Since Platform 3.5, a local JCR index can be used on each node of the cluster. It is a new feature and it needs a special configuration in Platform (described below).
All nodes must have the read/write access to the shared file system.
It is strongly recommended that you use a mount point on a SAN.