Used Tape Drive - New, Used or Refurbished Computer Parts Tape drive, tape autoloader, tape library, how to buy a tape drive, refurbished tape drive, used tape drive, autoloader

Chances are good that you’ve turned to this web page because you are faced with the decision of selecting a tape backup unit for your system or organization. This can be a much tougher decision than that of selecting a printer or disk drive. There are more than ten entirely different and incompatible tape technologies such as DAT, AIT, DLT, SDLT, LTO, etc. In addition to picking one of these technologies, you may also be faced with selecting the correct interface, deciding how you want to physically mount the drive and identifying the correct media (tape cartridge).

9 TO 5 COMPUTER specializes in the sale and support of tape products, including tape drives, autoloaders and libraries. Over the years we have helped hundreds of customers select the right products for their unique applications. Based upon the questions we have been asked and the advice given, and have prepared this document to help you make an intelligent decision. The information is organized as follows:

Specification Overview- a look at most of the important specifications you will encounter as you review competitive information. In addition to the obvious spec’s like storage capacity and backup speed, we’ll look at such things as the interface, size/mounting and upgrade path.

Tape Technology- just enough information to allow you to understand the differences between the widely different technologies. The best tape drive for backing up a small desktop computer may not be suitable for a server. We’ll look at DAT, AIT, DLT, SDLT, LTO and many more.

Software and Media- Once you’ve selected the right drive for your application you are still left with some more decisions: How do you get the drive or library to write or read? What tapes should you buy and how to handle and store them?

Specific Overview | Storage Capacity | Data Transfer Rate | Media Compatibility | Cost of Drive and Supported Media | Drive Interface

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Specification Overview
All tape drives do essentially the same thing, they write data to a removable media and when required read the data back. However, in terms of specifications such as storage capacity, data transfer rate (speed) and of course cost, the variations are enormous. An 8 GB (Gigabyte) Travan drive costs less than $100 while a 200 GB SDLT has an MSRP (Manufacturer's Suggested Retail Price) of over $5,000!

Before we look at, and compare, the available different types of tape drives and tape libraries let’s take a look at the important specifications. Which specifications are most important to you depends on your application. Understanding what they mean is the first step in making an intelligent decision. We have listed the specifications in order of their general importance to an average buyer. You may order them differently.

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Storage Capacity
This is the capacity using the longest length/highest capacity compatible media. It is expressed in GBs (Gigabytes). One GB is 1000 MB’s. Often both uncompressed and compressed capacities are listed. Most tape drives have built in hardware data compression (chip set on circuit board). Compression algorithms eliminate wasted space such as blank spaces or long strings of all 0’s or all 1’s by replacing them with references. Typically, with "normal" office document type data this can increase the capacity (and the data transfer rate) by 2 to 3 times. But, watch out! Data which has already been compressed, such as JPEG photos, MPEG video’s and other graphical data can not be further compressed. In fact, you might actually see a small decrease in storage capacity if you try to compress already compressed data.

If you know how much data you need to write (for backup, archiving, distribution, etc.), it is relatively easy to narrow you choice to drives with a similar capacity. If for example you want to back up your 80 GB hard drive in your desktop workstation you could use a low cost 20 GB (compressed) Travan tape drive or a 24 GB (compressed) DDS-3 tape drive. In this case, 4 tapes could store the entire 80 GB hard disk in compressed format. Most tape software allows you to span data across multiple tapes. Of course the capacity of the tape only needs to equal the amount of data that you wish to write to the tape. You could only back up the data files or only the files that have changed during the past month to reduce the number of tapes required.

Changing tapes to accommodate a lower capacity drive can be cumbersome and care needs to be maintained to insert the tapes in the correct order. A tape drive whose capacity equals or exceeds that of your entire disk storage capacity makes the job a lot easier. You could choose either a 40/80 GB DLT 8000 or a 50/100 GB AIT-2 to back up the whole drive in one continuous session. But, these drives cost a lot more money.

Remember that when we refer to capacity we’re really talking about the capacity of the tape media. If you put a 15/30 GB DLT III media in a DLT 8000 drive you still only get 15/30 GB of storage.

Since tape drives can write to one after another tapes to increase capacity, tape libraries have become fashionable for backing up large servers. Tape libraries hold 7, 30, 100 or even 1000 tapes in bins and use robotics to insert or remove these tape to or from the very same drives used individually. If a library has one 80 Gigabyte DLT8000 and has 100 tape bins it can store 8,000 GB’s or 8 Terabytes.

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Data Transfer Rate
Just as there is a wide variation in tape drive storage capacities there is a big range in the speed at which drives write or read data. Data transfer rate is expressed at MB/sec (Megabytes per second) and can be converted to MB/min or even GB/hr by simple multiplication. A low cost Travan tape drive writes at less than 1 MB/sec while an expensive LTO, SDLT or AIT-3 blasts data up to 30 MB/sec.

A word of caution. Drive manufacturers often list both sustained data rate and "burst" data transfer rate. "Burst" refers to rate that data can be moved to or from the tape drives internal data buffer. This is more dependent on the SCSI bus speed than performance of the tape drive mechanism. SCSI 3 can burst data at up to 160 MB/sec. However the burst data rate will have nothing to do with how long it takes to backup your 80 GB workstation drive or your 2 Terabyte server.

Data compression, mentioned earlier, also has a direct affect on the data transfer rate. If data compression doubles the drives storage capacity it also doubles the data transfer rate.

So, you now think you know how long it’s going to take to back up your 80 GB hard drive. You’ve decided to buy a relatively fast AIT-2 with 6 MB/sec uncompressed and 12 MB/sec compressed data transfer rate. You multiply 12 MB/sec by 60 seconds and get 720 MB/min. Multiply this again by 60 minutes and you’re at 42,000 MB/hour or 42 GB/hr. That implies that you can back up the whole drive in just under 2 hours. It would be nice, but it’s not the real world. The drive can write continuously at 12 MB/sec (it’s really recording 6 MB/sec, compression is in the electronics). However, data must be broken down into blocks which adds overhead to both the drive and the software that you are using. Whenever the tape drives data buffer runs out of data the drive must stop writing, back up to the last written block then go forward and resume writing. This is a very time consuming operation. In addition the drive may have to perform error correction. In reality the 12 MB/sec is significantly reduced.

Of even greater impact on the real backup speed or time is the verify operation. Normally you will perform a verify data comparison. This involves reading all of the data written to the tape and comparing it with the data on the hard disk. In the real world it will take 5 or 6 hours to back up a full 80 GB drive, assuming that the data was 2X compressible.

Wow! That means that the same tape drive would take days to back up a 2 or 3 TB server. That’s where multi-drive libraries incorporating the latest tape drive technologies, such as AIT-3, LTO or SDLT are very valuable. If one AIT-2 can back up 80 GBs in 5 hours, then 10 AIT-2’s all working in parallel can back up 800 GBs in 5 hours or perhaps 2 TBs overnight. However to do this you need to have enough SCSI interfaces and computer system "horsepower" and software to keep all 10 drives busy.

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Media Compatibility
This can be the number one selection criteria to some buyers. If you already have a large investment in DLT tapes (as an example) and you don’t want to abandon them, then the most logical addition or upgrade drive is one that can at least read those tapes. Quantum has done a good job of maintaining DLT compatibility with at least the two prior models. The DLT 8000 can read and even write to tapes generated on DLT 2000XT’s, DLT 4000’s and DLT 7000’s. (Beware … the DLT 1 is not a compatible technology, in either direction). The AIT 2 can read AIT 1 tapes and a DDS 4 DAT can read DDS 2 and DDS 3 tapes.

Compatibility with a service bureau or processing service can also be a key criteria. Companies that provide DVD authoring services require data to be supplied on DLT III or DLT IV media.

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Cost of Drive and Supported Media
While not usually to be found on the data sheet or spec. the combined cost of the drive and necessary media is a key decision factor. The cost of the drive (look at market cost not MSRP) is pretty easy to measure. However, the cost of media varies greatly even when calculated on a cost per GB. DDS 3 tapes store 24 GB (compressed) and can be found for as little as $6 a piece. The LTO and SDLT tapes store a lot more data but cost over $100 each.

The QIC tape drive now made only by Tandberg Data and now called SLR technology, with capacities up to 100 GB can be bought very cheaply and has great performance. However the tape cartridges are almost impossible to find and are very expensive from a limited number of retailers.

Just how important the cost and availability of the media is to you depends on how you will be using the drive and the generated tape(s). If you are planning to buy one or two tapes and keep reusing them over and over for weekly or monthly back up then perhaps you should look for a low cost drive with moderately expensive media. If you’re distributing data or filling a vault with archival data then the cost of the tapes may be more important than the cost of the drive.

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Drive Interface
Most, but not all tape drives now use one or another form of Small Computer Systems Interface (SCSI). However, within SCSI there are a number of different standards (SCSI-1, SCSI-2, SCSI-3), different hardware implementations (Single Ended SE, High Voltage Differential (HVD) and LVD) and different connectors (Internal drive, External, 50 pin narrow (8 bit) , 68 pin wide (16 bit), etc).

The difference between SCSI-1, 2 or 3 is of minimal importance when considering a tape drive. The data transfer rate of tape drives is slow compared to hard drives and even SCSI 1 supports most of the commands needed to control a tape drive.

The choice between the three SCSI hardware implementations can be very important and many drive models give you a choice of two.

SE (Single Ended) is the oldest and most common interface. It consists of 8 or 16 data lines and a number of control lines each having one active wire (which goes from approx. 4 volts to 0 volts) and is referenced to a common ground. The SE interface can only support a SCSI cable length of up to 18 feet from controller to last drive on the cable. SE SCSI works with most common SCSI adapters found in PC’s, Mac's, servers, etc. The choice of 8 bit ( 50 pin connector) or 16 bit (68 pin connector) is dependent on the tape drive model. Most newer devices now have 68 pin (16 bit) connectors.

HVD (High Voltage Differential) supports much longer cables and is less sensitive to electrical noise. For this reason most tape libraries and tape drive arrays use drives with HVD interfaces. HVD uses two wires for each data and control signal. As one of the pair goes from high to low the other goes from low to high. A total cable length of up to 80 feet, from system to last SCSI device may be used. HVD drives require special HVD SCSI adapters like the Adaptec 2944, 3944 or Buslogic 958D and HVD terminators. In addition you can not connect non HVD drives (with SE or LVD interfaces) to the same adapter. The connector used on HVD drives and adapters is an identical "Micro 68" SCSI wide connector use for SE/LVD drives.

LVD (Low Voltage Differential) is the latest SCSI interface technology and combines features of both SE and HVD. Most, if not all LVD SCSI adapters and drives will operate in either the SE or LVD mode. In the LVD mode cables up to about 40 feet may be used. One important peculiarity of LVD is that all of the devices and the adapter must operate in the same mode. If you mix a SE tape drive on the same cable/adapter as 5 or 6 LVD hard drives then all of the hard drives with shift to SE mode of operation.