General Tape Drive Information

In the realm of networks and open systems data backup, recovery, interchange and file access applications, the tape technology choice comes down to this: 4mm, 8mm, DLT and 3490E tape drives. Following is a comparison of the relative attributes, both positive and negative, of these vastly different tape technologies.

3490E Tape Drives

This is, and will remain, the tape technology of choice for IBM-compatible systems from RS/6000 servers to midrange AS/400 systems to legacy mainframe systems. Although 3490E holds only modest data capacities by today's standards, it contains high-end attributes embraced by mainframe users.

Advantages: Fastest access time-to-data (thread/load/ready). Widest acceptance as an interchange standard. Highest demonstrated data reliability. Easily automated media handling. Most robust tape cartridge for shipping and handling. Lowest cost media (per cartridge price). Demonstrated media shelf life of 15+ years.	Disadvantages: Lowest capacity per cartridge. Highest drive cost.

DLT 7000 Tape Drives

With 35Gb native capacity, DLT7000 leads in terms of sheer capacity. DLT and 8mm technology have been "leapfrogging" each other in terms of capacity growth in recent years (8mm EXB-8500 with 10 Mb, then DLT4000 with 20Gb, then 8mm Mammoth with 25Gb, now DLT7000 with 35Gb). The DLT7000 installed base is growing fast due to its high capacity. Although the DLT7000 transfer rate is 5 MB/sec, the performance is often underutilized because VO performance of many systems is optimized around 3 MB/second.

Advantages: Highest cartridge capacity. Fastest data transfer rate. Small form factor. Medium cost drive.	Disadvantages: Slow thread/load/access time. Expensive media (per cartridge)- emerging applications being written for DLT.

8mm and 4mm Tape Drives

Contact recording devices that put the media in contact with a quickly rotating helical scan R/W head. Although all helical scan drive manufacturers have reduced the potential for tape damage by de-tensioning the tape during periods of inactivity, it is still contact recording, with inherent limits on the number of passes the media can make. De-tensioning adds an additional performance penalty for the time needed to re-tension the tape and continue the R/W operation. Exabyte Mammoth and Sony SDX are the latest 8mm tape drive offerings. Both claim to have made significant improvements over initial 8mm designs.

8mm Advantages: High cartridge capacity. Moderate data transfer rates. Small form factor. Low cost devices. Fast cataloging of data (with SDX optional MIC "memory in cartridge" feature). Backward read-compatible with existing 8mm Exabyte installed base (Mammoth). Existing applications written for 8mm.

8mm Disadvantages: Slow thread/access time. Perception that helical-scan contact recording has shorter data life. Few applications yet for MIC (SDX). Helical scan R/W heads have a finite life, and replacements are expected, thus adding to the cost of ownership for this technology. Tape shelf life: Mammoth is projected at 30 years; DLT at 10 years. Neither have been around long enough to have DEMONSTRATED the projected media shelf life. Expensive tape cartridges.

4mm Advantages: Moderately high cartridge capacity. Small form factor. Low cost devices. Existing applications written for 4mm.	4mm Disadvantages: Slow data transfer rates. Slow thread/load/access time. Perception that helical-scan contact recording has shorter data life. Helical scan R/W heads have a finite life, and replacements are expected, thus adding to the cost of ownership for this technology.

DLT vs. 3490E Tape Drives

DLT 7000 has the highest cartridge capacity of any existing tape drive. This is it's primary advantage. Drawbacks include an extremely slow thread/load/ready time (80 seconds vs. 13 seconds for 3490E). This specification limits DLT's effectiveness as an interchange device where fast loading and access to data is a requirement. Not all applications have been written to take advantage of DLT's higher capacity.

In an IBM environment, the software is optimized around assigning one job's output to one piece of media. In this case a customer's job may use only 1 GB or less of the DLT tape's potential capacity of 35GB. In this application, the cost of DLT media would be significantly higher than storing real-world data on 3490E tape because DLT7000 cartridges cost approximately $75 each versus $6 for 3490E cartridges (end-user list prices).

Because of it's relatively recent availability, DLT7000 has not been established as an "interchange" medium for distributing data between sites.

Although DLT7000 transfers data at 5 MB/sec versus 3 MB/s for 3490E, the slower DLT thread/load times means that DLT has little performance advantage over 3490E (which will have threaded, loaded and transferred over 200 MB in the time it tasks the DLT7000 to thread/load/become ready). Furthermore, if the system cannot stream data at S MB/sec to or from the DLT7000, the DLT will need to reposition (which it does slowly), thus negating the advantage of the higher potential data transfer rate.

Compared to DLT, 3490E is low capacity and high priced. However, DLT is no match in terms of 3490E's fast backup/recovery speeds or file access performance.

Examples:

• 3490E can backup or recover 10 GB/hour per drive (20 GB/hour with 2: 1 compression).
• 3490E with "2x tape speed" can backup or recover 20 GB/hour per drive; 40 GB/hour with 2: 1 compression M4 Data's 2x speed drive is the model M490F).
• M490F with 2-drive autoloader can backup/recover 80 GB/hour (with 2:1 compression).
• 15 cartridge 3490E mini-library provides fastest access to 24 GB data (2:1 compression).