Comparing host-based D2D to VTLs for backup and restore: Part 2.

VTLs offer the "best of both worlds." IT administrators have enough problems to face in their existing environments without creating new ones by integrating multiple vendor products in an attempt to improve their backup system. Another, more advanced ATA disk-based backup solution has appeared on the market, one that provides all of the benefits of a traditional backup system with the benefits of a host-based D2D system, while removing the problems provided by each. The VTL offers IT administrators the best of tape technologies while delivering performance, reliability and scalability of disk. It represents a solution that is far superior to traditional tape-based data protection systems.

A VTL is a disk-based backup system that emulates one or more tape libraries and/or tape formats. The VTL is a completely integrated solution, which includes the tape emulation server, the ATA RAID arrays, and a file system optimized for tape backups. In many cases, additional proprietary hardware and software is included by the vendor that is designed to provide additional backup and restore functionality or enhanced performance. The VTL can also provide the same media management (tape cataloging, media expiration, etc.) capabilities that the administrator is used to, while most host-based D2D systems fail in this regard.

Because the VTL is a completely integrated solution, the issues mentioned in the previous sections about compatibility, integration and installation are no longer a concern for the IT administrator. As such, the VTL should arrive from the vendor configured and ready to install into the existing network environment. In most cases, regular backups should be possible in a very short time (even within minutes), with little or no changes to the current backup policies set in the existing backup application. When the backup job runs, it will deposit the data onto the VTL just as it would onto a tape library, only many times faster. Restores will also be many times faster.

The other file system problems discussed previously regarding performance and security are also no longer a concern. This is due to the fact that the file system for a VTL is typically proprietary and designed to act similar to a tape system with performance of ATA disk. ATA disks perform well when executing streaming reads or writes, but their throughput drops drastically once random seeks occur. For example, SEPATON's Disk Dynamic File System allows large I/O streams to execute efficiently and has the built-in infrastructure to dynamically balance performance across all available disks in their VTL appliance. The Disk Dynamic File System has the important side effects of not only sustaining maximum throughputs, but also dynamically load balancing I/O streams without any requirement for performance "tuning". The Figure represents the comparison between the backup of 20GB of data using a host-based D2D system and a VTL (SEPATON's S2100). Note the resulting performance increases possible with a VTL and its optimized file system.

It is notable that while the VTL was able to complete the backup of 20GB of data over twice as fast as an off-the-shelf host-based D2D configuration, the same VTL was able to backup 80GB of data over two and one half times faster than the D2D system. This shows that the file system performance advantage actually increases as the quantity of data being backed up increases!

One of the reasons that the VTL outperforms the D2D system during backup is that the backup application writes a backup to the VTL disk in much the same manner as it would to tape--in long continuous streams. The D2D, on the other hand, writes individual files and must record each file location and metadata to the file system before moving on to the next. This same method the VTL uses for writing streams of data instead of individual files prevents the VTL from encountering the limitation on the number of files its file system can support. The proprietary nature of the VTL file system overcomes the other file system limitations that the D2D experiences with its general-purpose file system.

With regards to security, accessing the file system of the VTL is like accessing that of tape. A user cannot gain access to a tape directly, nor can a virus-infected file infect a tape, as it cannot access the files as it would on a typical file system. The file system in most VTL appliances prevents viruses or other security threats from wreaking havoc on the system. A typical host-based D2D system and its general-purpose file system will not have the ability to provide this security, resulting in potential data loss for the organization--the very problem it is supposed to avoid.

Drawing Some Conclusions About VTL

The information provided regarding the difficulties of tape backup was likely not news to anyone--in particular to IT administrators who have been living with the problem for years. It is important to understand the specifics of the tape challenge, however, in order to seek out the best possible solution or technology. ATA disk is just such a technology, and it was shown that the best possible read and write performance comes at the best possible price with this technology. In other words, the performance to cost ratio is higher with ATA that any other disk technology that might be used in place of tape. The cost has finally dipped low enough to spur the development of disk-based solutions to the tape backup nightmare.

We saw that host-based D2D provides significant performance benefits, and many of the benefits that are being sought by IT administrators looking to implement disk-based backups. Host-based D2D integrates with existing backup applications, and provides performance enhancements but, as we discussed the integration, compatibility and support concerns could outweigh (and out-cost) the benefits of the solution. Moreover, the ongoing "care and feeding" of a D2D solution will quickly erode any staffing cost benefits that were originally realized.

Virtual tape library technology is the most promising technology available that will allow IT administrators to leverage the existing investment in their backup infrastructure while moving forward to gain the advantage of ATA disk enhancements.

Virtual tape library solutions are:

* Easy to implement, often installed and backing up using existing applications in minutes

* Easy to integrate, as they look like a standard tape library to your applications

* Flexible, as there are a number of scenarios with which they will work

* Scalable, like disk arrays, in that they can be expanded to back up hundreds of terabytes

* High performance! (Can be 10 times faster than traditional tape libraries.)

VTL technology captures all of the benefits discussed for host-based D2D, and then adds even more. The choice for IT decision makers should be clear: Virtual Tape Library appliances are the best choice for disk-based data protection.

20GB Backup Data

 5:31  20GB Backup S2100 #1
11:54  20GB Backup D-2-D #1
 5:32  20GB Backup S2100 #2
11:50  20GB Backup D-2-D #2

80GB Backup Data

19:52  80GB Backup S2100 #1
48:20  80GB Backup D-2-D #1
19:35  80GB Backup S2100 #2
49:24  80GB Backup D-2-D #2

Note: Table made from bar graph.

Part 1 appeared in September CTR. To order back issues, contact: [e-mail]

Paul Feresten is vice president, marketing, SEPATON, Inc. (Southborough, MA)

www.sepaton.com