WANs Extend SANs, File Services

By Henry Baltazar  |  Posted 2005-02-21

WANs Extend SANs, File Services

During the past few years, a number of technologies have emerged that meet the need for extending the reach of storage. From a business point of view, there are many reasons for purchasing and implementing storage extension technologies. Thanks to new challenges such as regulatory compliance mandates, the overwhelming growth of data, and a steady stream of mergers and acquisitions, IT managers now more than ever must be able to control storage resources while giving employees and business partners access to geographically dispersed information.

eWEEK Labs recently evaluated a number of systems that allow organizations to extend file services and SANs (storage area networks) over WANs to make information and resource sharing more efficient.

With file services consolidated in a central area, it becomes far easier for IT managers to add storage on demand (as opposed to shipping storage units out to branch offices). This centralization also makes it easier to take advantage of SRM (storage resource management) and quota management tools.

Most products developed to help IT managers enable file sharing over great distances can be grouped into a new category called WAFS (wide-area file services). Tacit Networks Inc., DiskSites Inc. and Cisco Systems Inc. (through its acquisition of Actona Technologies last year) are just three of the vendors currently offering WAFS solutions.

WAFS offerings extend the reach of CIFS (Common Internet File System) and NFS (Network File System) services over a companys WAN links.

With their ability to make CIFS and NFS run faster on a WAN, WAFS products allow IT managers to centralize file storage at a main office site while giving workers at remote offices high-speed access to files .

The WAFS products that eWEEK Labs has evaluated are different in many ways, but we have also seen a lot of common technology among them in the areas of intelligent caching and protocol optimization.

One of the first solutions we tested at eWEEK Labs was Tacit Networks iShared appliances (previously called Tacit Storage Cache and the Tacit Cache Server).

With the Tacit system, an appliance has to be installed at the central site as well as at all remote offices. These remote appliances act as caches, giving clients at remote sites local read/write access to files via CIFS and NFS.

To speed things up on the WAN, Tacit uses a proprietary streaming data replication protocol called SC/IP (Storage Caching over IP) that keeps data on caches updated. The protocol works bidirectionally, allowing files to be written and altered at either the main office or branch office.

During tests with the iShared appliances, accessing "warm" files (files already populated on the cache) from a remote office was as quick as accessing the files locally. Performance was a bit slower when accessing "cold" files (noncached files) from a remote site, but it was a definite improvement compared with access speeds without the Tacit system.

The DiskSites solution, like Tacits, is appliance-based. The DiskSites FilePort appliance sits at a central site, while the FileCache appliance is located at remote sites. However, while Tacits solution is more of a proxy cache unit, the DiskSites system is focused on file replication. When setting up a file share with the DiskSites system, a remote user sets up shares directly mapped to the home server; with the Tacit solution, in contrast, users map shares to the local cache.

This slight difference in implementation did not make the DiskSites solution any less effective in our tests. In fact, the DiskSites solution adds capabilities such as DNS (Domain Name System) and DHCP (Dynamic Host Configuration Protocol) services to the appliances, making them a good choice for companies that want to manage network services from a central office.

Riverbed Technology Inc.s Steelhead appliances are a third player in the WAFS space, and Riverbeds products are the most uncommon among the current crop. The Steelhead appliances analyze and segment data and use proprietary algorithms to recognize and accelerate transactions. If data segments are recognized, the appliance closest to the remote user can deliver the data to the user.

Besides accelerating CIFS, the Steelhead solution can accelerate Microsoft Exchange, HTTP and FTP.

Click here to read a review of Riverbeds Steelhead 500 appliance.

Also available (but not yet tested by eWEEK Labs) is the Cisco File Engine Series Appliance, borne of Ciscos acquisition of Actona Technologies. Cisco has also entered into an agreement with EMC Corp. to sell EMCs Celerra NAS (network-attached storage) units, which Cisco plans to bundle with the Cisco File Engine to make a complete NAS and WAFS solution.

IT managers evaluating WAFS should expect to pay about $13,000 to $20,000 for a central office appliance and roughly $7,000 to $10,000 for each remote appliance. These prices are relatively low, considering the bandwidth and resources that will be saved by using them.

Next page: SAN over WAN.

Page Two

Just as file services can be extended over a WAN, so, too, can SANs—using storage protocols such as iSCSI, FCIP (Fibre Channel over IP) and Fibre Channel over SONET (Synchronous Optical Network).

Fibre Channel is a storage networking protocol, but its distance limitation is 6.2 miles. However, some regulatory guidelines are recommending that IT managers keep a minimum of 100 miles between sites and are requiring IT managers to demonstrate the ability to rapidly restore business services after a disaster.

One way to bridge this gap is to use FCIP, a solid choice for companies that are trying to create direct connections between two geographically separated Fibre Channel SANs. FCIPs biggest benefit is that it is transparent to the hardware sitting on Fibre Channel SANs. (Devices have no idea their data is being sent over a WAN.)

FCIP is limited to point-to-point connections (connecting one SAN to another), but it works well and is fairly mature. FCIP takes Fibre Channel data and encapsulates it in IP so that the data can be sent over WAN links. In a basic FCIP implementation, FCIP gateways are placed at both the central and remote site and are positioned between the Fibre Channel SAN and IP network. The FCIP gateways establish a tunnel between themselves across the WAN to connect the sites .

FCIP gateways act as bridges between the networks, encapsulating Fibre Channel data on the way out and stripping off the IP headers of received FCIP traffic before forwarding them to the Fibre Channel SAN.

Another IP-based method of extending SANs is iSCSI, a newer protocol and probably the best choice for companies on strict budgets.

iSCSI is a TCP protocol that encapsulates SCSI commands. Unlike FCIP, iSCSI enables direct connections between hosts and targets. While FCIP is clearly a complementary protocol to Fibre Channel, iSCSI can be used as a replacement for Fibre Channel in environments that dont need high performance. (iSCSI is considerably slower than Fibre Channel.)

iSCSI is an IP-based protocol, so it does not require the addition of expensive Fibre Channel host bus adapters and switches to create a SAN.

Storage vendors LightSand Communications Inc., McData and Cisco also sell channel extender products, another means of extending SANs over WAN links. Unlike the IP solutions previously mentioned, these products maintain the Fibre Channel protocol through the WAN links. They also deliver much better performance than one would normally see in an IP solution.

To compensate for the latency on long-distance links, these gateway devices are loaded with credit buffers—large memory pools that provide a steady flow of information from SAN to SAN.

Channel extender products are the best choice for high-performance, synchronous replication of data. Channel extenders can use a variety of links, including SONET, dark fiber and DWDM (Dense Wavelength Division Multiplexing).

Senior Analyst Henry Baltazar can be reached at henry_baltazar@ziffdavis.com.

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