Supporting Electronic Vaulting with Todays Communications Technology
By W. Carol Cleigh
To reap the benefits of electronic vaulting for your organization today, you must carefully consider the capabilities of various
channel extension systems. This article provides information to help you evaluate the existing technologies that provide remote
channel support for electronic vaulting.
What are the choices?
Your basic choice will be between a channel extender, and a channel attached network.
Channel extenders serialize data that is parallel on the channel, transmit it to a similar device at the other end, which then returns it to parallel for the device (in this case, a tape). They may also add parity, or CRC codes and headers to check the integrity of the data, or perform other basic communications tasks.
Channel attached networks function as channel extenders in their simplest form, but they add more extensive routing, error detection and correction and network control capabilities. The network may also add other capabilities.
What is the difference?
The capability to re-route around a line failure. A channel extender is typically point-to-point - it goes down if the phone line goes down. Networks allow you to triangulate the system with one line provided to back-up multiple other lines (see figure 1).
The capability to perform well over long distances. To use electronic vaulting, it may be necessary or desirable to communicate to a vault location that is far from your data center. This may be needed because your recovery company is in another city, or because you are in an area that is prone to wide area disasters that would affect the local recovery center as well as your location. A fully developed networking technology allows you to choose your vault location(s) with little regard to geographic distance. Channel extenders often are very distance sensitive.
Robust error detection and recovery. Channel technology was developed for local devices, and the error recovery incorporated in it assumes direct cabling. Obviously, there are a lot of things that can go wrong in the real world outside of the data center that cannot happen when the cables are less than 400 feet long. Networking technology, designed for real worldconditions is essential to successful electronic vaulting.
The flexibility to handle changing business environments. As your enterprise grows, you need a system that can grow. Also, you want a system that has the flexibility to add capacity when needed at end-of-the-month or end-of-the-year. Networking technology which allows the flexibility to modify line speed or add lines when needed can reduce long term costs. Channel extenders generally do not allow for easy modifications to communications lines.
Support for other devices and computers in the same system. A fully developed channel network allows you to leverage your purchases for electronic vaulting by adding other devices and hosts that may need access to the vault and one another. Channel extenders can connect a number of hosts to the vault, but a network provides connections between the hosts, and to other devices.
System management and control. Although a channel extender is typically a black box that you cannot open, a network must have a competent network management system to monitor activity.
Why would I ever want a Channel Extender?
System Cost. If you have a simple application that will never grow, and the cost is significantly less, channel extension technology is for you. But, even initial cost differences are often negligible, or even favor the network.
What other communications decisions will I have to make?
There are several other decisions that affect your choice once you have decided upon basic technology.
Host software modification or transparency. Most channel extenders and some channel networks are transparent to host software. If you choose one that is not, you may find that the changes to the host operating system become a major issue.
Support for standards. Most channel extenders, and some networks are closed systems -that is they use protocols that are inherently incompatible with other systems. The trend in data communications is toward standard or open systems that allow multi-vendor access to the network. The benefit to you is that standards simplify interconnection and support, and they keep you from being locked in to a single vendor.
There are several options for high speed media available today, each has advantages and disadvantages.
Private fiber optics should be considered if you have a campusenvironment or a creative local telephone company, and you wish to establish your vault very close to the data center. This technology involves installing your own fiberoptic cable, or obtaining a suitable cable from the phone company. Fiber optics gives you near channel speed, but distances are severely limited. The typical fiber optics system supports up to 2km (144 miles), but some are limited to as little as 400m (440 yards) when tape drives are attached.
DS3 (also called T3) is a technology that is available from some telephone companies for use in local metropolitan areas. It allows for private point-to-point communications at 44M bits per second. It is, pending FCC approval, being made available for long distances, but this may take some time. In the interim, you should consider DS3 if your vault is in the same city as your data center. However, in choosing a technology for DS3, look carefully at the speed that is actually made available to transfer data. Some DS3 systems actually deliver significantly less than 44 M bits per second.
T1 telephone lines can be used over wide areas at speeds of 1.544M bits per second and are generally available in all parts of the country. Unlike Private Fiber Optics and DS3, the technology for T1 has been available for some time and is standard. T1 has the additional advantage of allowing you to change your line configuration to meet changing needs (through ACCUNET dial, available from AT&T, or similar services from other carriers). Some systems are able to marry multiple T1 connections to yield a higher speed. Be careful in choosing a vendor that supports T1 to ensure that they have no arbitrary distance limitations, and that T1s of different distances can be married. Telephone companies often route T1s without regard for the shortest possible distance. You may want your telephone company to route your T1s by different routes so if one goes down the other may not.
How does all of this add up?
Deciding on the best system for your enterprise may seem daunting, but here are a few basic questions that may help:
Where will my vault be located? This determines the media and speeds available.
How much data will have to be transmitted in a given amount of time? This determines the speed and throughput required.
Can I share with other communications requirements? This helps to determine the basic technology requirement.
How important are other issues like system management, software transparency and standards to my enterprise? If these are very important, your decision will be simplified, since few channel extension systems, or channel attached networks provide these features.
Once these questions have been answered and prioritized, you are ready to establish an electronic vault.
This article adapted from Vol. 2 No. 1, p. 12.
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