Global access enables you to make a path on one cluster accessible to clients of one or more remote clusters without the clients having access to the source cluster. A global access configuration specifies a source path on a source cluster and one or more destination paths, each on one destination cluster. The data at the source path is not synced to the destination paths but it is immediately accessible for read and write requests at the destination paths as soon as the global access path is created.
Data that clients request to read at a destination path is requested from the source and cached by the destination clusters. When a destination cluster receives a read request for data that is not cached, the destination peer reads the data from the source and prefetches other relevant data and metadata from the source.
If data is accessed multiple times in a given time-frame, the destination peer requests a lease on the data. For the duration of the lease, the destination peer answers read requests on the leased data without refreshing the data from the source. When the lease expires, the destination peer invalidates the cache. The next time the same data is requested from the destination peer, the destination peer fetches the data again from the source. The lease expiration time is configured per global access source path.
Clients can also write data to the path. The write requests are sent to the source path.
The source path must be a path that exists prior to configuring the global access. Multiple destinations are supported per source path. The destination path must be a new path created as part of the configuration.
Supported Protocols
Global access supports NFSv3. This means that clients with an NFSv3 mount to a path on destination cluster have visibility and access to paths under the mount path that are shared by global access.
For example, consider a cluster (the source peer) with a protected path /a/b, which is replicated by Global Access to a destination cluster as /x/y.
On the destination cluster, a view is created for /x for NFSv3 (and possibly other protocols).
An NFSv3 client that mounts /x will see /x/y (which replicates /a/b from the source cluster) and have access to it. A client for a different protocol will only see /x but not /x/y.