Implementing Fibre Channel Strategy For Tape Backup.

The basic architecture for tape backup and archive systems has remained unchanged since the introduction and subsequent wide-scale implementation of the LAN (Local Area Network) over 15 years ago. More recently, the advent of Fibre Channel technology has made possible the implementation of new tape backup system architectures that hold significant advantages in three areas--increases in system performance, elimination of potential system bottlenecks, and an overall lower total cost-of-ownership. These advantages greatly benefit systems administrators, network engineers, and, ultimately, the users who rely on these systems. Two new Fibre Channel-based architectures are currently available that deliver these advantages--Fibre Channel-based LAN-free backup and server-less backup. These backup solutions are worthy of examination by users, system administrators, and financial administrators alike because of the performance and cost advantages that both architectures possess. Specifically, this article outlines current tape configurations and explains the system architectures for both LAN-free and server-less backup solutions. The specific advantages of each will also be examined and a suggested strategy follows for implementing a LAN-free and a server-less Storage Area Network (SAN) solution for tape libraries using Fibre Channel-based technology.

Current Tape Architecture

The typical current tape backup architecture for large systems uses tape backup servers and LAN (Local Area Network) resources. In this architecture, information that is contained in on-line storage and accessed though file servers or application servers (database servers, data warehouse servers, etc.) is pulled across a l00baseT Ethernet LAN by a tape backup server to which the tape library is attached.

As Fig 1 shows, there are several elements that can potentially act as bottlenecks to backup system performance. First and foremost is the LAN itself. Ethernet is, by storage standards, slow and constrictive. LAN performance is one of the major reasons for less-than-desired backup performance. Backups also tend to diminish overall performance in the LAN due to the large amount of data that streams through at once. The result is a reduction in performance for users on the network segment to which the tape system is attached--reducing overall system efficiency.

The servers themselves represent a bottleneck, as well, especially the file server. The collateral effect of reduced performance in the file or application server is slower overall performance for users attempting to access information through the server. In many cases, the file server cannot service end-user requests at all during backup periods. The tape server is less affected. However, it too represents a potential choke point for the system. Finally, the relative slowness of the tape units (to disk storage) also represents another, though small, bottleneck on overall system performance.

LAN-Free Backup Architecture

LAN-free backup involves application of Fibre Channel technology to the tape storage subsystem to increase the overall performance of the entire storage system by eliminating the need to pull data over the LAN and through a file or application server. Typically, LAN-free backup solutions are deployed using a tape server, tape library, and disk-based storage, all attached directly to a Fibre Channel infrastructure shown in Fig 2. The tape library is attached to the Fibre Channel network via a bridge device, which also acts as a hardware buffer for incoming data.

In this design, the tape server can stream data directly from the storage to the bridge device at 85 to 90MB/sec. The only bottleneck becomes the speed of the tape library itself and the realized throughput of the tape server.

Server-Less Backup Architecture

Server-less backup takes the LAN-free solution one step further. In this architecture (Fig 3), the tape server is delegated the role of "system coordinator," rather than data mover. In a server-less backup configuration, a copy device assumes the task of actually moving data from the disk storage to the tape library.

Typically, a server-less backup solution is composed of the hardware infrastructure deployed for LAN-free backup with the addition of two important elements. First is a specialized bridge device, capable of acting as a copy device or independent data movement unit. The bridge device is present to actually move the data. Secondly, there is the addition of specialized control software, which issues commands to the copy device and insures smooth operation of the entire system. A tape server is still necessary, but it now functions as a place to house the control software rather than as a system device dedicated solely to moving data.

The copy device is an application-oriented element with sufficient and specialized resources to perform specific, rather than general, activities within a network or SAN. In the case of a copy device for server-less backup, the device must have enough computing power and memory to support the movement of large blocks of data. The copy device must also support connections to other disk drives and tape libraries that may be involved in the movement of the data. Finally, the device must provide a software interface that allows it to interact with software applications that wish to control, manage, and track the movement of data in the SAN. Currently, the Extended Copy Command interface is the most popular interface for these types of applications.

Advantages

* Advantages of the LAN-free configuration

Both the LAN-free and server-less backup architectures possess significant advantages. The main advantage of the LAN-free backup approach is increased throughput to the tape devices and, as a result, shorter backup times. By removing the Ethernet bottleneck (2-8MB/sec), the performance envelope is now most affected by the throughput of the tape units themselves (12-20MB/sec). The result is a performance increase of 3 to 10 times--an immediately realizable gain in efficiency. Use of tape RAID software can also boost performance by aggregating tape device bandwidth in the same manner as disk RAID.

LAN-free backup also leverages existing assets, keeping cost-of-entry to SAN architectures manageable. Thus, LAN-free backup may be viewed as an "upgrade" to an existing tape storage sub-system, rather than as an entirely new installation. By having the ability to re-deploy existing system assets in a new manner, thereby extending the lifetime of those assets, a return on the initial capital investment of those assets is realized. Time-to-implement is also significantly shortened, which leads to more immediate benefits to the system and to the users, combined with a reduction in the overall cost of implementation.

Aside from the obvious financial benefits, LAN-free backup delivers service increases that will positively affect end-users. Since the LAN is not involved, there are no longer heavy loads placed on it or on application servers during backup periods. This enables higher overall service levels and better application response times. LAN-free backup helps ensure that backups are complete without disruption to other systems. This in turn reduces adverse effects of backups on normal business operations.

* Advantages of The Server-less configuration

While not as dramatic as the advantages of LAN-free backup, there are significant gains to be found that are unique to the server-less architecture. As opposed to the increased throughput to the tape devices with the LAN-free configuration, removing the remaining bottleneck in the server-less configuration creates performance gains in another important area--the tape server. Even in LAN-free backup, the backup server's performance is directly related to the memory, I/O, and CPU performance of the backup server itself. These constraints are eliminated as the data moves through a high-performance copy device, optimized for data movement, rather than through a general-purpose computer, bound by multiple needs and a non-specific architecture.

With server-less backup, significant cost savings may be realized with the elimination of expensive, high-end servers and the substitution of relatively inexpensive copy devices and readily available low-end control servers. Since specialized control software such as Celestra can usually share space on another server, the dedicated tape server may often be eliminated altogether for additional cost savings.

Another advantage unique to the server-less architecture is the ability to stream the same data to several tape libraries simultaneously, even if geographically separated, without the need for copying and moving the actual tapes. This provides an important advantage in a disaster recovery plan.

Finally, the system's overall architecture becomes simpler--an important benefit for system administrators. With server-less backup, a general-purpose server that previously required significant administration and maintenance is now replaced with a standalone device that requires virtually no maintenance and can be replaced quickly in the event of failure. Coupled with the previously outlined cost savings, the result is a lower total-cost-of-ownership for the backup sub-system and system infrastructure.

Suggested Deployment strategy

Users may upgrade existing systems to LAN-free Backup by merely deploying a bridge device and other Fibre Channel components. This has the advantage of testing the hardware infrastructure before moving to a server-less backup configuration. It is advantageous to begin here because the step forward is not as radical and still delivers an immediate system enhancement.

Upgrading the existing system to a server-less backup configuration is the next step. Users may note that this step is not unilateral--users may upgrade the LAN-free systems to server-less configurations where desired. Since this is likely done through software updates to the bridge device, as opposed to hardware additions, this provides a method of achieving increased functionality at a low incremental cost with little risk. Any risk is also mitigated by the ability to fall back on the previously implemented LAN-free backup system.

As need for more backup capacity grows, users may simply add additional inexpensive copy devices and additional tape libraries. It is at this point that the cost effectiveness of this solution becomes apparent. Instead of having to add additional servers (that each require extensive administration) and upgrades to the LAN, inexpensive copy devices are all that is required.

Likewise, as the speeds of tape devices themselves increase, so will the overall efficiency and performance of the entire tape backup sub-system. Since the tape devices themselves are the bottleneck, increases in system performance will be immediately realized when the performance rates of the tape units increase. As explained, current architecture places control of system performance with the LAN and server, rather than with the tape unit itself. LAN-free and Server-less backup architectures shift control of bandwidth and, hence, system performance to the high-speed Fibre Channel network, high-bandwidth copy device, and tape library.

In conclusion, by implementing a migration strategy away from the current server and LAN-oriented backup systems toward a Fibre Channel-based shared tape system, improvements in overall system performance and reductions in total-cost-of-ownership of the system will be realized. Furthermore, by extending the lifetime of existing assets, while increasing overall system performance and reducing operating costs, a better return on investment will also be realized.

Finally, end-users and companies alike will be served better by experiencing less disruption to their overall systems and, hence, regular business operations. For this ultimate reason, implementation of this strategy is worthwhile.

Tom Petrocelli is the Fibre Channel product manager of ATTO Technology, Inc. (Amherst, NY)