Server Clustering
Networked storage enables multiple servers to assume the tasks of a failed server.
Server clustering requires failover software on each server.
Servers monitor the status of the cluster via a heartbeat protocol.
Server clusters are typically provisioned with dual data paths through the SAN.
Tape Backup
Traditional LAN-based tape backup requires multiple block-to-file conversion processes.
SAN-based tape backup enables block transport for backup.
Extended copy (third-party copy) agents can move blocks directly from disk to tape, taking the server out of the backup data path.
The integrity of a tape backup process requires validation through testing or restore.
Data Replication
Data replication provides a current copy of data on a separate disk mirror.
Software-based data replication requires that the host system perform write operations to two separate arrays.
Disk-based data replication performs direct disk-to-disk write operations.
An active-passive configuration is based on a primary and a secondary storage array.
An active-active configuration enables each array to be primary to itself and secondary to another.
Synchronous data replication requires completion of writes to both arrays before notification of write complete to the host.
Asynchronous data replication spools pending writes from the primary to the secondary array.
Synchronous data replication may be sensitive to speed-of-light latency over long distances.
Distributed File Systems
In a shared nothing configuration, each host is assigned its own LUNs.
File sharing must be managed to safeguard against overwrites and data corruption.
A distributed file system presents a uniform view of data to all servers in a cluster.
Cache coherency requires that each host have the most current version of a file in its cache buffers.
Device Memory Export Protocol (DMEP) maintains file cache on the storage arrays instead of the host systems.
Applications such as Sistina Global File System (GFS) can interact with DMEP to provide file locking and managed updates to a distributed file system.