Tape drive is one of the most economical affordable, reliable and effective ways to store, transfer and manage data. The need for computer users to backup their workstations and servers are many folds. Since, the value of data often exceeds the value of the computer system later within weeks of installation of the sysytem.. Many factors can cause the loss of data - power blownout, power failure, human error, harddisk failure and other natural disasters. In many cases, the lost data, if not properly backup, is simply not recoverable. In other case, data may still be re-assembled or re-captured from other system either electronically or manually, but both certainly involve a lot of cost and time.

Advantage of using tape drive as backup device

Tape drives offer the most reliable and affordable mean of backing up data. The principal advantages of tape drives for backup are:

a) Low cost per gigabyte for storage as low as US$1.3 per gigabyte.
b) Fast transfer rate (up to 6 MB/sec compressed data).
c) Removable cartridge allows easy storage and safe custody in off-site locations.
d) Well proven reliablitity for most drives and cartridges for storing data in long run. Tape drives have been used to store most important data on mainframe computers for over 30 years with proven track records.
e) Tape drives allow easy unattended automatic backup. Numerous mature software are available in the market that allow users to backup and recover data of large network during pre-defined period without any operator attendance. Online database backups are also available through any tape device.
f) Tape drives offer high data storage capacities up to 40 GB of compressed data on one cartridge. With well proven autoloading mechanism using the latest high performance tape drives, such library system can be easily expanded to provide storage capacity up to terabytes level with enhanced data management.

While uninformed computer users are often tempted to use other ways to backup their data, but actually none of these offer the complete range of advantages which tape drives do. A list of the principal drawbacks of some of these so called alternative backup are as follows:-

Non-tape backup device	Disadvantages
Hard disk	Expensive data stroage per GB. Hard disk cannot be removed from system and data could be lost if there is a fire or other disaster on site.
Magneto Optical Drive	Relatively expensive storage per GB. Slow data transfer rate. Relatively new technology that data integrity (after storage an cartiridge over a long period of time) is not fully proven.
Floppy Disk / Floptical / Zip Drive	Small capacity. Slow transfer rate. Need a large number of diskettes to handle 1 GB data.
Jazz Drive	Expensive storage cost per GB. New technology uproven in terms of reliability and data integrity.
CD-Recordable	Limited capacity and reliablitity. Error correction method not reliable enough for totally secured backup requirements. Slow transfer rate and cannot allow unattended and scheduled backup.

II. Tape Drive System: Basic Elements and Classifications

There are two major parts in a tape drive system. First, a drive mechanism which contains a tape winding / rewinding mechanism with magnetic head to write or record data on a tape. Second, a tape cartridge system which contains a magnetically coated tape of varying length and width. (depending on the technology), that can be placed in the drive mechanisum and brought into contact with the magnetic head to record or transfer data. These two elements are inter-related, while the tape mechanisms are designed specifically to work with a specific type of tape cartridge.

Elements to evaluate a tape drive

There are eight major determinants in assessing the performance, reliability and capability of a tape drive system.

1. Tape width

The first and easiest way to classify ape technology is to use the width of the tape cartfidge which the drive mechanism would work.

The importance of tape width lies in that for a given length of tape, the wider the tape the more recording area is available for storing and transferring data. For tape with the same coating material and a given magnetic recording density, a wider recording area can obviously provide more room for further improvement in data transfer rate and data capacity.

2. Native capacity ad transfer rate

The second most important determinant which is related to the tape width is the native capacity and transfer rate. Computer users must use the native capactiy and transfer rate for comparison, because this is the most likely method of recording data and represents the actual performance you can achieve most of the time. Some tape drives vendors publish the capacity and transfer rate after software compression assuming a 2:1 ratio which could be nisleading for two reasons. First, the compression achieved depends on the nature of the data and very often people cannot get a 2:1 increase in capacity and transfer rate after compression. Secondly, for general backup purpose, it is not advisable to use compression as very often the individual application program may have already
compressed the data file in the first place. Higher capacity can be achieved by having either a wider tape, longer tape or higher recording density or a combination of all. For professional backup, particulary for networks, the data transfer rate is very important. Most companies have only a short time slot for backing up their network servers. Prolonging the length of a tape to acheieve higher capacity without corresponding improvement in data transfer rate would be a serious limitation, as the user may never have enough time to backup the full capacity of the tape.

3. Recording Technology

The third determinant is how the data are recorded and written on the tape by the recording head. In general, there are two methods; linear recording and helical recording. The linear recording method records data in a straight line in parallel with the tape and is adopted by most technologies including 3480/3490, DLT, Single / Multi channel Linear Recording by Tandberg Data, and Travan. It provides a simple head design with a relatively less complex head and drive mechanism, requiring less moving parts and less tension on tape and hence less wear and tear on tape. The helical scan method uses a rotating recording head with data written on tracks at an angle to the tape. This method generally allows more data to be written on a narrower width of tape. The media cost of such method is generally low but it does require a more complex head and tape drive mechanism, with correspondingly disadvantage in terms of durability of drive mechanism (because of more moving parts) and tape life (because of high tape tension and more moving parts in touch with the tape and hence more wear and tear).

4. Data Verification

The fourth determinant is whether the recording method uses a reliable drive mechanisum which allows the tape drive to verify the data as it copies the data on the tape. This method is known as Read While Write (RWW), and is a feature demanded by professional users to ensure that the data they backup is a fully reliable copy of the original, and that any discrepancy is remedied immediately as the data is written on the tape. RWW is achieved by having read and write heads in series so that the 2 functions are carried out simultaneously. This require more-expensive recording heads and more sophisticated electronics but can ensure that all data backup are reliable. Most high performance tape recording methods for network, workstation, mainframe use the RWW or a similar incorporates technology. These included Quantum DLT, ODI 3480/3490, Tandberg Data SLR/MLR, Seagate (DAT), Exabyte (8mm). For tape drives made for home users or small office workstations, RWW technology is not commonly used. This includes most mini-cartridge products (except the Tandbery 3520, 3720 which are developed with RWW) and all current Travan products. Some software such as Cheyenne has a function for vertifying data after write but this would significantly slow down the tape drive performance.

5. Tape cartridge Life

The fifth most important determinant in selecting a tape drive is the tape cartridge cost and the tape cartridge life. A common measurement of the media life of cartridge is the number of tape head pass over the tape which the tape allows and still maintains data integrity. In general, the one time purchase price of tape cartridges for helical scan tape drives such as DAT, 8mm are the lowest. These cartridges are of a simple design (complexity of the recording mechanism rest in the drive unit). However, due to their design and the nature of the drive mechanism on which such tape cartridges are used, they are not as robust as the SLR/MLR and Travan cartridges in terms of media life, and ability to withstand more hostile storage environment such as heat and humidity. The SLR/MLR and Travan cartridges are more expensive but are generally more long lasting and robust. Because they have been introduced into the market for many years, there are well proven statistics to demonstrate the ability for such cartridges to retain data even after a prolonged storage period of 10 years or more.

6. Backward Compatibility

The sixth most important criteria for selecting a tape drive is backward compatibility in terms of reading and /or writing back on cartridges that stored in older version format. With the tremendous improvement in computer technology and increase in data storage requirements, organisations very often have to upgrade their tape backup system in line with their computer system. Valuable data kept on cartridges years ago may however sill be required from time to time. It will be much more convenient if the new tape drive can read back the data written on the cartridges used in older generation drives. The DC6000 series of tape drives from Tandberg Data offers the best performance in this regard. Their new Multichannel Linear Recording (MLR) drives offering 13 GB native storage capacity and transfer rate of 1.5 MB/sec but still can read back 120 MB, 250 MB, 525 MB, 1.2 GB, 2.5 Gb & 5 GB DC6000 cartridge data written by previous Tandberg Data drive models. Without full backward compatibility, organisation may find it necessary to incur extra cost and less efficiency in data conversion.

7. Interface

The seventh important criteria in selecting a tape drive is the interface, The most commonly used interface for tape drives are Floppy. IDE, SCSI and parallel port. Floppy interface provides the simplest and lowest cost solution as the floppy controller is already in every PC system. The drawback is that floppy interface cannot allow high data transfer rate. In some cases, manufacturers provide an accelerator card to be plugged in the motherboard to enhance the transfer rate but this defeats the original purpose for using the floppy interface for simplicity and low cost. The use of such addition controller could also cause transferability problem in that cartridges written by one tape drive many not be fully read by another tape drive. The IDE interface offers a simple and convenient connection to the tape drive, as most PC system have multiple IDE connections with a spare part for a tape drive. The problem with IDE tape drives is that the performance of IDE could be reduced substantially under a multiple user environment. As such, IDE would be more suitable for stand-alone single station backup applications and seldom used as the main disk interface for networks. Also, as the IDE interface was developed previously for the harddisk, interchange compatibility is still sometimes a problem, as cartridges written under certain PC motherboards may cause read or write problem when put into another tape drive operating under other PCs.

The SCSI interface offers a solution which has the fastest performance and best compatibility for tape drives. The use of new generation Ultra SCSI. Wide SCSI, Ultra Wide SCSI and even optical fibres will further enhance the performance of high end tape drives such as the Tandberg MLR, Exabyte Mammoth and Qunatum DLT 4000 and DLT 7000 drives.

Parallel port connections are based on either a parallel port to SCSI, parallel port to IDE or a parallel port to floppy interface connector. The parallel port provides a very convenient way to connect tape drive to computers using external parallel port devices. However, such units are more costly than the corresponding direct floppy. IDE or SCSI connection. Depending on its design, the parallel port connector may also slow-down the overall data transfer performance and / or cause some compatibility or interchange problems.

8. Reliability

The eighth factor to consider in selecting a tape drive is the reliability of the drive. Unfortunatley, this is not a factor which can be assessed objectively with reliable data. Due to different ways in which different manufacturers defines MTBF, this is not usually a good comparison. The warranty period offered by the vendor could be a guide reflect how durable or reliable the tape drive is, but this is not in itself an absolute measurement either. The application used and general operating environment could also make the reliability and durability of different products varying from market to market. The best guide on reliability is the actual experience using the drive in the market, either by the customer himself or from a referral from someone who has that experience. In a market like China, users' general experience is that the use of a technology with more robust design and allowance for margin of error is more recommendable. Users should consult reliable dealers and distributors experienced in supplying tape drive system in that market for advice if they have any doubts. From experience in the China market, DC6000 data cartridge drives have found to perform with the best reliability and durable in all operating environments.

III. Tape Autoloaders & Libraries

Given the increasing demand for automatic data backup and management for large networks, there is increasing demand for tape autoloaders and libraries using multiple cartridges and robotics to increase the storage capacity of the tape devices as well as to allow authomatic handling of data. The engine used in these libraries are primarily higher performance tape drives with soft loading, with autoloaders having primarily single tape drive and multicartridge while libraries having mulitple tape drives and cartridges. Tape libraries offer the best security with redundancy and is gaining more and more acceptance.

Exabyte has been the market leader in supplying tape library systems and has the largest installed base of such systems in the market. With the use of Mammoth, the Exabyte 220 offers users the fastest transfer rate and performance among tape technologies of its class. DAT libraries on the other hand offers a low cost starter system at low performance, which could meet the needs of automatic backup in smaller systems. For users preferring to use linear recording solution for high reliability, 3490 libraries, DLT libraries and Tanberg Multichannel Linear Recording MLR libraries offer a good variety of choice on performance and capacity at different price range. Of those catergories, 3490 libraries would be the most expensive, followed by DLT libraries and the MLR library.

Vendor	Basic Drive Unit Type	No. of Drives Per System	No. of Cartridge	Data Transfer Rate / Drive	Tape Capacity	Access Time
Seagate	DAT	1	4, 12	500 KB/s	4/8*GB	30 to 40* sec
Tandberg	MLR1	1, 2, 4	10, 20 or 40	1.5 MB/s	13/26*GB	45 sec
Quantum	DLT	1	5, 7	1.5 MB/s	20/40*GB	68 sec
ODI	DLT	1, 2	10	1.5 MB/s	20/40*GB	45 sec
Exabyte	8mm	2, 4	20, 40, 80	3 MB/s	20/40*GB	25 sec
ODI	L3940E	1	10	3 MB/s	800MB/2.4* GB	30 to 40 sec

IV. Software Support for Tape Drive System

The selection of the best tape drive system depends not just on hardware but also the software. For standalone tape backup systems for home users or single station PC users, Seagate software offers the most price competitive and best features to maximise the usability of the tape drive. Seagate now offers total Windows and Windows 95 plug and play, multimedia information, installation and tutorial for easy installation. More significantly Seagate and other software vendors now offer direct tape access solution enabling users to use simple command in Windows to drag and drop files onto the tape just like other storage device. Users can see the tape directly and all the files information under Windows and can retrieve by the mouse click. Given the low cost of data storage offered by tape drives on cost per gigabyte basis, tape drives provides a simple, cheap and effective way to store near-online data, as it effectively allows you to use your tape drives like a hard disk or floppy disk or Zip drive but with much higher capacity and lower cost. Your tape drive will appear just as an additional drive in your system allowing easy access for the transfer and storage of files. Major applications include showing large image or data files download from internet or from CD-ROM.

For network backup on servers, users can use some standard utilities offered by operating systems such as the S-Backup for Novell and MS-Backup under Windows. But these utilities offer very limied functions and do not allow scheduling and other more advanced automated data management features, Cheyenne is the market leader in providing direct backup on server solution covering Novell Netware, Windows NT and UNIX, supporting all major tape drive products on the market. Addition features such as database agents offered by Cheyenne and other vendors allow users to backup while the integrated database systems on Oracle, Sybase and Groupware solutions such as Lotus Notes are in operation. This is most important for global organization serving users around the world in different time zones and for which there is little or limited time for the system to be shut down for backup.

V. Conclusion

One of the most important function of tape drives is to backup data accurately before they are lost. This is like buying an insurance to protect important corporate data. Selecting the right tape drive hardware and software solution with the function and performance meeting your requirement and fitting your budget is most important.

Given the variety of products and technology available in the market, you are well advised to seek the advice of a well established tape drive dealer or distributor with proven experience of the operating condition in that market. The same dealer or distributor should also have a wide network of infrastructure to provide after sales support to ensure that your tape drive system can be integrated and put into use with optimum performance after purchase. The same network should also be able provide good and reliable warranty support as well as technical advice on any further requirement for upgrade.

Laser Computer Limited has 15 years experience in supplying computer peripherals and software in Hong Kong and China. With 13 years experience in supplying tape drives system and related products, Laser is the most experienced distributor of such products in the region. Laser is by far the largest supplier of tape system consistently for the past 12 years in this market and has the most well proven experience in advising and supporting such applications. Laser's track record in supplying the most reliable tape drives to the market and our professional standing in this industry is underlined by the endorsement by most leading tape drives supplier in the world is their appointment of Laser as their distributor: Exabyte, Overland Data, Quantum, Seagate and Tandberg Data. Please call any of our offices in Hong Kong and China for advice and we will be most pleased to help you to select and use the best tape backup systems to suit your requirements and budget.