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- Locking open files globally to prevent multiple people from simultaneously editing a file
- Controlling which files get sent to specific remote offices and under what circumstances
- Transmitting only file changes when files are saved or closed
- Working in conjunction with existing remote file servers or by replacing them
- Minimizing WAN traffic
WAFS products--whether software or appliances--address different file-server configurations and enterprise needs. For example, Burlington, MA-based Signiant Inc.'s Mobilize product is deployed as an agent on remote file servers, but provides only point-in-time replication and lacks the edit locking and synchronous file services most WAFS products offer. Conversely, San Francisco-based Riverbed Technology Inc.'s Steelhead product is installed as an appliance in the network where it maintains real-time file consistency and speeds up the performance of all TCP network application traffic like e-mail.
Most WAFS software is intended for small companies/departments that need to keep their existing remote file servers and allow remote users to collaborate on files at near-LAN speeds. Hardware WAFS products deliver files at LAN speeds, and manage data and file servers centrally. Many WAFS products also offer disk caches that feature file segmentation, application optimization and data compression as standard features.
Software-only WAFS products require installing an agent on file servers at the data center and remote location. The storage administrator must configure which directories and/or files are replicated to the remote sites. (Tacit's IShared, classified as a hardware product in this overview, is also available in a software-only version which doesn't require server agents.) One distinct benefit that most software products provide and appliances don't is that they allow groups of remote offices to collaborate and share data using their existing file servers.
Signiant's Mobilize provides point-in-time file replication that can execute as frequently as once a minute to keep files consistent. Although Mobilize sends these changes in byte-level increments, it was originally designed as a data replication and protection solution. It's possible for files to become out of sync, however, if users at different locations start manipulating the same file in between file replications. To avoid inconsistencies, Mobilize includes file versioning that tracks file changes and can maintain up to 39 versions of the same file. If consistency problems do occur, someone must review each version of the file to determine which is the most current or correct.
Availl 3.0, from Andover, MA-based Availl Inc., is another software-only WAFS product. It tries to overcome potential file inconsistencies by maintaining a real-time copy of all files on the file servers it manages. Availl creates a mirrored disk cache on all of the different file servers. Every byte-level change to each file is mirrored to all of the file servers as changes occur. Availl claims this lets users at multiple sites work on the same file at the same time, and to see their edits and changes as they occur. But this real-time approach can give users a false sense of security; if a WAN link to a site fails, a file change at the offline site may still need to be reconciled if the file was changed at other sites.
The initial sync up of files between sites is a slow process and should be scheduled during relatively inactive periods or off-hours. To minimize network traffic, Availl and Signiant employ bandwidth optimization techniques such as data compression, and only send changes to files once the initial file synchronization completes. However, these products generate increased CPU and memory overhead, so the performance of busy file servers may be affected during peak times.
These two products also differ in the number of operating systems and file-sharing network protocols they support. Availl 3.0 supports Windows file servers and the CIFS protocol. Signiant's Mobilize works with a much wider range of OSes, including Linux, VMware, Windows and different varieties of Unix, and it supports the CIFS and NFS protocols. A major deficiency of both products is their inability to address the existence of NAS appliances such as Network Appliance (NetApp) Inc. filers or EMC Corp.'s Celerra.
This was first published in October 2005