Moving large amounts of data offsite is a difficult thing to do. It is difficult to beat tape drives and an automobile for rapid data replication. Obviously this method has serious limitations. With the rise of Shared Storage, most replication today occurs at the Storage layer. Though application layer replication offers major advantages, it is usually pursued in addition to storage replication.

What is storage replication? Most SANs and many NAS devices offers licensed replication as a feature. GCS' two favorite devices, the HP Lefthand and Dell Equallogic, include these licenses at no cost. By placing a SAN in-office and one at a remote data center, then connecting the sites with sufficient bandwidth, the SANs will replicate data between the two at the block level. This is an efficient method. Unfortunately, the SANs cannot differentiate between legitimate data changes (ie, a saved Word doc) and temporary data changes such as SQL log files. Everything is pushed across the connection. This tends to require large amounts of bandwidth.

The HP Lefthand offers both asynchronous and synchronous replication options. With asynch replication changed data is pushed at scheduled intervals. With synchronous replication the devices attempt near real-time replication. The HP Lefthand only offers synchronous when there is less than 20ms of latency between the sites. The HP Lefthand also offers bandwidth management on the SAN to help restrict the amount of bandwidth consumed on your site-to-site connection.

A readily apparent benefit of SAN replication is virtual machine replication. If my VMs are stored on my SAN, they are replicated to my remote sites. This dramatically reduces recovery time in a variety of outages.

GCS also recommends Microsoft DFS-R for replication of file stores. Simple, reliable and efficient, this technology allows Windows NAS devices to replicate between sites and provide failover in the event of an outage.

Petri reviews the new VMWare vSphere Data Recovery feature in a recent post. Most important to note is that there is added support for VSS for Windows VMs, no tape drive support and no agent/plugin support for SQL, Exchange, etc. This highlights one of the advantages Microsoft's Hyper-V has in comparison to VMWare, Microsoft's Data Protection Manager (DPM).  DPM is a mature, reliable backup software that offers tape support, VSS support, Exchange/SQL/Sharepoint agents and DPM-to-DPM replication. Now DPM Server is not included in Microsoft's System Center Server Management Suite Enterprise or Datacenter. However all agents for DPM are included. For another $600 you get a complete backup application.

Live Migration is the killer app in Hyper-V R2, which is due out in mere weeks. Microsoft finally can match VMWare feature by feature in many environments - or can they? If you don't want backups, Live Migration works fine. What? Again, please? If you're using Data Protection Manager 2007, you will not be able to backup VMs using Clustered Shared Volumes. Clustered Shared Volumes are required to utilize Live Migration.

Fortunately DPM 2010 released to Beta on 9/29. Not only does it add support for VMs using Clustered Shared Volumes but it also enables mobile laptop backups. The mobile laptop backups work over a VPN and are designed for the user off the LAN. DPM to DPM replication offers a poor man's disaster recovery solution.

Data Protection Manager is by far the best backup solution for Hyper-V virtualized environments. It includes brick level backup of Exchange, a SQL agent, and a Sharepoint agent. It integrates to Shadowcopy for backups of the VMs. All DPM agents are included in the System Center Server Management Suite, though you have to buy a seperate DPM server license.

Hold your breath. Live Migration is coming, just not quite as fast as the marketing indicates.