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File virtualization architectures
File virtualization appliances are available in four different architectures: out-of-band, a combination of out-of-band and in-band, in-band and split-path. Brocade Communications Systems Inc.'s StorageX is the only file virtualization appliance that stays exclusively out-of-band or out of the data path. It resides on a Windows 2000/2003 namespace server and creates a global namespace by discovering and indexing files on network file servers.
Client servers then access and use the StorageX global namespace in the following ways. Windows client servers discover the StorageX global namespace using the Distributed File System (DFS) client included with the Windows operating system. For Linux and Unix operating systems, StorageX updates the Network Information Service (NIS). These client servers then access files by first contacting the StorageX global namespace server, which provides the client server with the physical locations of the requested files. The client server then uses that response to directly access files on the network file servers.
While this architecture may work well for organizations aggregating file views across multiple data centers, some administrators may have a problem with how StorageX handles file movement. For Windows-based clients, StorageX's Replication Manager uses a native Windows-based replication agent to move files. However, on Unix and Linux hosts, StorageX deploys and installs its own replication agent that uses the NFS protocol to move files between different network file servers. This means StorageX has to have the appropriate security access to the Unix and Linux operating systems to install this agent, which may be a concern to IT shops that don't want to introduce another agent on their hosts.
EMC Corp.'s Rainfinity Global File Virtualization uses a combination of out-of-band and in-band techniques. Rainfinity stays out-of-band during the initial file discovery, but moves into the data path when virtualizing files. This requires administrators to create a virtual LAN (VLAN) in the network that allows Rainfinity to move into the data path between client servers and network file servers to virtualize files. When it does so, the Rainfinity appliance assumes the IP address and DNS name of the network file server. This causes the network to reroute traffic normally directed to the file server to Rainfinity, at which time Rainfinity takes control of file placement and movement among network file servers.
A feature that distinguishes EMC's Rainfinity from other file virtualization appliances is that it doesn't require the creation of its own namespace. The absence of a namespace was a determining factor for Brian Peterson, a storage architect with a Midwest food packaging company, who chose to use Rainfinity as part of his company's NAS migration and consolidation efforts. Because Peterson had previously implemented a NAS namespace within his company, bringing in another file virtualization appliance and converting to its namespace would have meant taking a single huge outage requiring the coordination of almost 500 people.
Because Peterson's corporation uses NAS so extensively, he needed protection against Rainfinity failing while operating in-band to ensure that enterprise applications wouldn't come to a halt. To prevent that, Peterson's team wrote what they called the "Big Red Button" script. The script allowed the operations staff to quickly take Rainfinity out-of-band and out of the data path of the servers, allowing client servers to directly access data on network file servers.
"The script provided the insurance we needed to insert the virtualization device into such a critical data path," says Peterson.
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