TAPE AUTOMATION AND THE MIGRATION FROM SCSI TO FIBRE CHANNEL.
Tape automation first became popular in the mainframe environment as a means to control tape mounting operations for large numbers of sequential files. Within the open systems environment, tape libraries appeared to automate the backup process by eliminating operator intervention and the resulting errors of manual handling. With SCSI as the dominant interface in the open systems environment, tape libraries and the tape drives contained within the libraries used the SCSI interface. Initially, a tape library was connected to a single server with backup software residing on that server. With the proliferation of distributed systems, IT installations began to have many servers, all with the need for automated backup. The choice was to put a tape library on every server, an expensive alternative, or to connect servers together across the network and utilize one or more servers to perform backup for the other servers. This contained the cost exposure of multiple tape libraries, but introduced the performance bottle neck associated with sending large amounts of backup data across a relatively slow network. The network would get congested and the effective transfer rate to the tape drives would suffer because of the network speed.
As the concept of the Storage Area Network (SAN) was accepted, the vision became multiple servers sharing a tape automation resource with high speed back end links from each of the servers to the tape library without having to send data across the front end network (LAN-less backup). Fibre Channel has emerged as the technology of choice for the high speed interconnect.
Before exploring the tape automation environment itself, let's look at how Fibre Channel implementations began with RAID systems. The easiest first step was to take an existing SCSI-based RAID system and hook it to Fibre Channel using a bridge/router. This required no new investment in the RAID system and the bridge/router would convert from the SCSI interface of the RAID system to the Fibre Channel interface of the interconnect infrastructure. The disadvantage was that the bridge/router was a fairly expensive add-on device.
The next step was for new RAID controllers to be introduced that provided Fibre Channel interfaces. The controller could attach directly to the Fibre Channel infrastructure and, within the RAID subsystem, the controller could communicate with SCSI disk drives.
The final step was to move to a full Fibre Channel implementation, whereby the RAID controller had a Fibre Channel interface to the outside Fibre Channel infrastructure and an internal interface to Fibre Channel disk drives.
Fibre channel implementations for tape automation are following this same three-step process that was followed by RAID subsystems. Today, the main approach being used is to connect an existing SCSI tape library to a Fibre Channel infrastructure using a bridge/router (Fig 1). Tape libraries have now come to market that have a Fibre Channel controller and can, consequently, connect directly to the Fibre Channel infrastructure (Fig 2).The final step will be an all Fibre Channel implementation, including a Fibre Channel library controller and Fibre Channel tape drives (Fig 3). Fibre Channel tape drives are just starting to appear and will become more prevalent over the next two years.
The need for Fibre Channel attachment of tape automation subsystems is being fueled by the growth of disk capacity and the resultant amount of information that needs to be backed up to tape. With more servers that have more disk space requiring timely backup of precious corporate information resources, IT professionals face an increasing challenge to provide an effective backup solution. The specific requirements fall into three categories: storage management control, shared resources, and performance.
* Storage Management
With a mainframe installation, storage management is centralized. With distributed computing, servers reside in multiple locations and the management of storage becomes more of a challenge. As the size of the network grows, the ability to effectively backup data, maintain a consistent storage management process, and protect the variety of storage resources becomes more of a problem. Some organizations have attempted to deal with this by recentralizing the servers, bringing the servers back into a common location. Others have attempted to recentralize the storage resource while still keeping the servers distributed. The main challenge is to provide central control of storage even if the processing and storage resources themselves are distributed. Fibre Channel offers the interconnect infrastructure that can facilitate improved storage management, connecting multiple servers and storage subsystems across a campus environment.
* Shared Resource
As much as those of us in the tape automation business would like to sell a tape library for every server, this is not the cost-effective way to go. Tape libraries are an ideal shared resource for use across multiple servers. One IT executive shares this perspective, "One of the problems we have today with backup is most of the world considers that you backup one server at a time. You need some way to have multiple servers use a single tape library. A tape library is more expensive than a server. There is no way you can buy a tape library for each server." A complete Fibre Channel solution with appropriate software and switches/hubs can make this a reality.
One of the challenges of a networked computing environment is providing enough bandwidth to accommodate processes such as backup. Current networks aren't fast enough to support existing tape drives. As stated by one IT manager, "A lot of places are still on 10baseT for the backbone but everyone is moving to switched 100baseT or faster networks. That's a limitation in itself. The network is being used for things that it was never intended for." Another IT manager shares this perspective, "The interconnect to the storage is related, since if you use the network to interconnect between disparate servers, then the network becomes the bottleneck." A systems integrator adds, "The tape drives are faster than the network. We're looking at customers who can't do their backup at night because there isn't enough time. So they come in the morning to log in and have to wait for backup to complete." This problem will only be exacerbated with the improved performance of tape drives that are coming to market within the next year. A Fibre Channel SAN offers a pipe big enough to feed these tape backup devices. When presented with a Fibre Channel solution at a focus group, an IT systems administration manager clearly summarized, "With this technology, I see some significant advantages with speed, particularly backing up. As a backup solution, it is much more attractive."
SCSI has been the dominant technology to connect tape libraries to servers in open systems. With the emergence of Fibre Channel solutions, there exists an improved capability to address lingering IT problems of storage management control, shared resources, and performance. Tape automation using bridges/routers is the initial approach being implemented. The next step includes Fibre Channel controllers in the tape libraries and, finally, there will be Fibre Channel capable tape drives in the libraries.
Mike Befeler is the vice president of marketing and business development at Benchmark Tape Systems (Boulder, CO).
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|Title Annotation:||Industry Trend or Event|
|Publication:||Computer Technology Review|
|Date:||Jan 1, 2000|
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