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Tacit Storage Cache/ Tacit Cache Server

Tacit Networks products allow NAS to break out of the LAN and onto the WAN.

Using a combination of low-latency replication and caching technologies, the Tacit Storage Cache and the Tacit Cache Server work together to allow NAS to be accessible over WANs. (The products must be used together.)

NAS products run file-sharing protocols such as CIFS and NFS to control data access and link remote clients to files. Although these protocols work well in LAN-type environments, performance slows to a crawl when clients are linked to NAS units over a WAN.

The obvious reason for this performance degradation is that WAN links are typically far slower than whatever is running on the LAN. The difference in data throughput between LANs and WANs, however, isnt the only reason for the degraded performance. A subtle, but far more important, reason for the degradation lies in the manner in which protocols such as CIFS and NFS work.

Both of these protocols are chatty, an attribute that can be tolerated in high-speed LAN environments but is extraordinarily painful when coupled with WAN latencies.

In Tacit Networks solution, a streaming data replication protocol (SC/IP) replaces CIFS and NFS over WAN links. SC/IP ensures that Tacit Storage Cache appliances (which are installed at remote sites) have an accurate and complete copy of the data sets stored at the home office.

Unlike other caching solutions we have seen, most of which push out read replicas to remote sites, Tacit Networks solution can support read/write storage caches. This provides users in remote sites with the ability to update and maintain shared data on an equal playing field with workers in the home office.

The Tacit Cache Server sits in front of a primary NAS system at a data center, and it coordinates communications between the NAS and the remote offices. The Tacit Storage Cache sits at remote office sites, where it holds an identical read/write copy of the primary data set that remote users can access without depleting WAN resources.

Currently, communication between the Tacit Storage Cache and the NAS device must be via NFS. (CIFS is not supported yet.) The back-end NFS limitation is expected to be overcome within a month or so.

Since data is cached at each local site, network administrators can conserve bandwidth among sites by using Tacit Cache Servers. Once data is replicated to a Tacit Cache Server, users can get to it via CIFS and NFS.

When data is updated at a remote site, the Tacit Storage Cache calculates the data changes, compresses them and sends them back to the primary NAS system.

In tests at eWEEK Labs San Francisco offices, instead of waiting seconds or even minutes to access various files from a remote data center in New Jersey, the Tacit Cache Server gave us virtually instantaneous access to our data.

The Tacit Storage Cache costs $22,500, while Tacit Cache Servers cost $21,500. The products began shipping in February.

While Tacit Networks solution is the first we have seen that tackles the NAS-over-WAN challenge, there are a couple of other vendors to keep an eye on in this space.

The WebOffice Inc. VPSN (Virtual Private Storage Network) system blends intelligent file transfer technology with VPN technology to create a secure private network.

WebOffices S-Transfer technology keeps track of file transfers so that the process does not have to begin from the beginning in the event of a machine or network failure.

WebOffices system integrates a switch, firewall, NAS and VPN in a single box, which makes it ideal for small-office environments.

eWEEK Labs has not had a chance to compare this unit with the Tacit Networks solution, but based on what we have seen so far, these products have some similarities. More information can be found at

Another vendor to watch is DiskSites Inc., whose W-NAS solution is closer to Tacit Networks because it combines caching capabilities with compression. For more information, go to

Tacit Executive Summary

Senior Analyst Henry Baltazar can be contacted at

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