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Selecting the right CDP product architecture for enterprise servers often comes down to whether the server is connected to a network or an FC SAN. If connected to an FC SAN, you need to determine if there are sufficient changes to application data to justify the deployment of an FC SAN-attached CDP appliance.
CDP products for network-attached servers come in many different architectures. CA XOsoft, for example, installs at the file-system level and is configurable as a standalone product and as a replication target on a secondary server.
VMware users may want to consider FalconStor's CDP Virtual Appliance for VMware. Although both CA XOsoft and FalconStor Software support VMware and the installation of host CDP agents on guest OSes, FalconStor installs its host CDP agent at the block level. The agent then stores the changed data to a volume presented over the corporate IP network by the FalconStor CDP Appliance. Once the CDP software creates a copy of the data on that virtual volume, the admin may break off that virtual CDP LUN from the source and present it to any other OS on that ESX server for recoveries or testing and development (see "CDP and VMware," below).
| CDP and VMware
Here are a few items to consider before proceeding with continuous data protection (CDP) on VMware servers.
CDP host agent. CDP host agents are only compatible with VMware guest OSes and will require administrators to install host agents on each guest OS. This may require the allocation of additional storage to each guest OS for locally cached writes by the CDP host agent.
Hypervisor agent. This feature, under consideration by CDP vendors, will protect all guest OSes hosted by a VMware ESX server. However, restores can only occur for the entire VMware ESX server, not individual guest OSes on the VMware server.
CDP server and network overhead. CDP doubles the number of writes on each guest OS, so administrators should ensure that the VMware server has sufficient server and network resources to accommodate the extra load.
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Ruden McClosky, a Florida-based law firm, deployed CDP in 2005 to protect its corporate and remote-office network-attached servers. Ben Weinberger, IT director for the firm, implemented CA XOsoft for its remote-data protection, which let him recover a file to any previous point-in-time on any of his 24 Windows servers located statewide. "We survived two direct hits to our Fort Lauderdale data center without data loss or downtime," he says.
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