8.5 Chapter Summary

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.



Designing Storage Area Networks(c) A Practical Reference for Implementing Fibre Channel and IP SANs
Designing Storage Area Networks: A Practical Reference for Implementing Fibre Channel and IP SANs (2nd Edition)
ISBN: 0321136500
EAN: 2147483647
Year: 2003
Pages: 171
Authors: Tom Clark

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