Wide Area File Systems - WAFS - are about waving goodbye to servers in remote offices. Or are they? You still have a server in the branch office but it is now conceptually part of the networking gear and a slave of a central server, managed and used by it. The aim is to have file and application response times at the remote office as if the users there were connected to a local file server on a LAN. But there is no local file server. Instead servers have been concentrated at a data centre and various technologies are used to provide LAN-like speeds across a wide area link.

Expand Networks has just launched a WAFS product. It comprises software, obtained from a partnership with DiskSites, in a new release of its Expand O/S and three new network Accelerator boxes which have hard disks for file caching. These disks can be pre-populated with files at remote offices. Typically with a WAFS the first requester of a file has to wait for it to come across the WAN. Subsequent requesters get the cached copy much more quickly. Expand's pre-population means the first user wait period can be abolished

Expand's Accelerator boxes can compress data in the TCP stream both at the byte and object level. They also send out a flood of TCP packets without waiting for individual packet acknowledgements, so-called spoofing. These techniques can accelerate business data traffic, such as database records, three or four times, the company says.

There is also a datacentre-located layer 7 management and quality of service (QoS) function. There is no need for agent software in the remote offices as part of this. It detects remote office Accelerator boxes and records the types of data flowing to them. With this information an administrator can define service levels so that, for example, voice-over-IP traffic has a high service level. It won't be affected by another user at the remote site requesting a large FTP transfer.

Of course, the FTP user doesn't get the LAN-like speed they may be expecting then but that is what you get with QoS trade-offs when link traffic approaches capacity.

If the WAN fails then remote users work with cached data only. Saves are held in the local caches. When the link is back then Expand's software saves everything back to the data centre and ensures that file updates are properly synchronised.

Adam Davison, Expand's VP Sales EMEA, makes the point that a remote office file server often doesn't just serve files. It will be a print server and a DNS server and so forth. So the Expand Accelerators have these added functions. He says: "They are virtual servers. You have to have a holistic approach." This comprises the network acceleration, the WAFS technology, application plug-ins and central monitoring and quality of service functions.

Only then can you have a virtual server in the remote office which requires zero IT support skills there.

Is WAFS storage or networking?
A wide area file system sounds like a storage concept. The Expand Accelerators are located between the routers that front end the network links and the site IT kit. They 'see' everything that goes along the WAN to the routers.

This means they don't 'see' upstream storage infrastructure such as a NAS or SAN system, not unless the supplier has worked with a SAN or NAS supplier to enhance traffic of NAS or SAN data across the LAN.

Tacit Networks has worked with Microsoft to integrate its WAFS technology with Windows Server 2003, which is used by many NAS vendors, and so better present centralised NAS files across a WAN.

WAFS can't work without networking techniques to speed up WAN data transfer. These techniques basically enable the WAN to carry less data. Data is compressed. Only changed data - the delta - is sent up and down the link when possible. Caching at the remote site obviates much data transfer. TCP spoofing reduces the need for a large proportion of the packet-level acknowledgements in TCP.

WAFS systems need to try every techniques they can to reduce link traffic. So there are typically application plug-ins to, for example, speed up Citrix terminal traffic, as Expand does, and also Oracle, SAP, Exchange or Notes/Domino.

So a WAFS needs storage technologies, WAN technologies and application technologies for it to do its job well.

Local file server substitution
The Expand Accelerators run an embedded Linux O/S. Here we have a Linux box emulating the functions of a Windows server. Oddly, considering it's a Unix system, it doesn't support NFS yet; Davison says that is coming.

What would make the life of WAFS suppliers technically easier would be if Microsoft provided a version of Windows suitable for running as a remote office server slaved to a data centre.

It would make life easier as all the local file server functions could be performed by such a box. But it would alter Expand Networks' business model because of the resulting Windows licence fees.

Competing WAFS products
Brocade has made an investment in Tacit Networks. Its WAFS product offers both CIFS and NFS support and also offers TCP acceleration. Like the Expand product it can cope with WAN outages.

Other competition comes from Cisco with technology based on its Fineground and Actona acquisitions, and Juniper which bought Peribit for similar technology.

Riverbed also has WAN outage capabilities.

Eventually a WAN outage will reduce a remote office's ability to work. Expand offers hot stand-by Accelerators for remote offices with automatic fail over if the primary Accelerator fails. But if the link fails, a WAFS set-up can continue working on its caches only so long before the data synchronisation task becomes very difficult and caches fill up. Then WAFS stops.