A Better Architecture For High Availability
Data replication at the file-system level between two independent systems is a high-availability configuration that has many significant advantages over shared-storage clustering. The majority of existing high-availability installations use a shared-storage clustering architecture, where multiple servers each connect to external RAID subsystems. However, this architecture presents several hurdles to eliminating data loss and to achieving high availability. A high availability system based on disk data replication over TCP/IP between two completely independent systems does not have these shortcomings. This replication architecture, not widely used for high availability until now, offers higher availability at a lower cost than the commonly used shared-storage clustering architecture.
An architecture based on data replication instead of shared storage contains no single points of failure and enables sub-second failover as file system recovery time is eliminated. The cache and lock management issues that plague shared-storage clustering are not present in data replication architectures. The transparency of replication and the avoidance of many of the intricate problems faced by clustering means that replication offers an ease of implementation and maintenance that contrasts with the complexity of clustered configurations.