Snap Shot and Remote Replication go Open Source
When I first came to Sun back in 1998 at the start of Sun's Storage group, they had just acquired the storage division of Encore in South Florida. This was in the heyday of big storage boxes with lots of value added data services and expensive enterprise class of service. Kind of like the mainframe of the storage industry. In fact these boxes were sold into the mainframe market primarily and were just then becoming attached to open systems as those systems grew up to replace the mainframe.
Storage and servers have moved on since then, and customers are building solutions from smaller, cheaper server and storage components. Unfortunately, a lot of the storage industry has not kept up with this trend. Large storage vendors still have a significant vested interest in charging huge sums to lock you into their expensive storage "services" tied to their large enterprise storage systems. Sun will sell you a box like this if you want, but perhaps you are following the industry trend and would like these services on cheaper hardware.
The services I am talking about are snap shot copy and remote replication. Snap shot copy at the block level is used to provide near continuous data protection underneath databases and filesystems, minimizing availability interruptions because access to the block device only has to be paused momentarily. During this short interval the software sets up structures to ensure that further writes diverge the original from the snap shot copy.
Remote replication sends changes over a network to a remote site for business continuance in the event of a site disaster. This can be done synchronously or asynchronously depending on the tradeoffs this imposes between availability and performance.
