Contacted by a managed storage services supplier I got to thinking about the difference between wide area file services (WAFS) and managed storage services. What is the difference? Both involve data stored at a remote site and accessed over a wide area network (WAN) link. Obviously there are pricing and sysadm differences from the buying IT department's point of view but what are the differences in the broad brush technologies and the user experiences?

In both cases the amount of storage at the remote or customer site can be reduced or constrained by having the data stored at the end of the WAN link. When a user or an application needs data what happens? In the simplest way the user or application sends a file open request to a remote disk or volume. It results in the file travelling back across the link to the user's system.

Network transit time has to be added to the file access time. Is this severe enough to make sub-file-level access to remote data impractical? Yes, it can be.

A WAFS service adds in technologies to reduce the effects of this network latency. There are network acceleration techniques to reduce the 'chattiness' of TCP/IP and other protocols. There are the provision of specialised boxes, like Riverhead's Steelhead which cache files at the remote end of the WAFS link. This is needed because the first delivery of a file across the WAN is slow. Only be having a cache box at the remote end can subsequent accesses to the file be at LAN speed.

These WAFS appliances also store writes if the link goes down for a short time. And they are involved in file locking when more than one person tries to write to the same file.

A WAFS product without these features would be a poor and slow product which is exactly what a managed storage services offering without WAFS features would be. Okay for remote backup ad archiving but no use at all for online file or record access.