NAS and SAN instead of Internal Lion Server Storage
You may want to look at two options for expanded capacity outside the Mac you choose to run OS X Lion: NAS (network attached storage) and SAN (storage area network), which, despite the acronyms, aren’t opposites
Network attached storage (NAS) is a stand-alone storage device that plugs directly into the network via Ethernet or wireless (802.11 Wi-Fi). You should definitely use Ethernet for connecting a NAS device to a server. Multiple servers or computers can access a NAS device directly.
The Apple Time Capsule is an example of a NAS unit, although the Time Machine software isn’t well suited to backing up a server. Other NAS devices with multiple drive bays are more flexible for use with a server. NAS units are often used for backup.
While a NAS is a low-end home/office or small to medium business device, a storage area network (SAN) is a high-performance, high-cost investment used as primary server storage in large networks. A SAN can be a subnetwork of hard drives connected with a high-speed Fibre Channel switch. Multiple servers can access a SAN, centralizing storage on the network.
Apple offers Xsan software ($999) that enables multiple desktop and server computers to directly access and share RAID storage. It can handle up to 2 petabytes, which is 2000 terabytes, or 2 million gigabytes.
The iCal Server that comes with Lion Server is optimized to work with Xsan so that multiple iCal Servers can access the same SAN storage. This server clustering enables iCal to serve thousands of users. Lion Server’s mail server is similarly optimized for Xsan. Podcast Producer can use Xsan to spread the creation of high-quality video to multiple servers all working on the same video located on the SAN.
If you want to bone up on SANs, try Storage Area Networks For Dummies, 2nd Edition, by Christopher Poelker and Alex Nikitin (John Wiley & Sons, Inc.).