With storage capacities growing by leaps and bounds, the need for effective backup is even more important. We look at your options.

The primary purpose for a tape drive is to store and back up data. By installing a tape drive with removable media, data can be physically stored away from your machine. Should your computer become unusable, your critical data files can reliably be retrieved with a minimum of effort.

There are many different strategies for protecting data, which brings on the debate about tape vs disk. Tape however still represents the most logical and cost-effective solution.

Tape vs Disk
Disk is now playing an important factor in data protection. Some of the key features of disk over tape are:

• Backup is much quicker than with tape
• Fast restoration can be crucial for mission critical data
• Users are less likely to know for sure whether a backup has successfully completed with tape
• Disk prices have fallen

Tape is essential in data protection for the following reasons:

• Offers higher storage capacities
• Automated tape libraries still offer lowest cost per GB
• Media is interchangeable
• Mirrored disks offer no protection against viruses, theft, or natural disasters
• Data can be stored offsite
• It has a long shelf life (30 years)

Generally with less mission-critical situations you would use tape; the more important the data is, the more likely it is you would choose disk. However, having a combination of these two technologies can ensure that all the bases are covered.

Storage requirements
In order to understand your business' storage requirements, you should work out what services are of paramount importance to you. A good way to optimise your operations in terms of cost and risks is by selecting the right backup and restore solution.

Picking the right solution to best meet your business needs may mean having a mixture of different solutions. For this review we were only concerned with standard tape storage devices. The Quantum DX30, which we also tested, would sit in either the business-critical or mission-critical storage set.

Deployment
One of the things you must do before deploying any sort of backup system is to create and adhere to a data protection strategy. This can be as simple as attaching a single tape drive to a server via SCSI or as complex as having multiple tape libraries connected to a SAN through Fibre Channel.

You should consider your current and future data requirements in terms of performance, capacity, and the backup window. Backup windows have shrunk as many enterprises that have gone global have become increasingly dependent on transaction-oriented systems. So to remain competitive, they can't afford to take key systems offline for too long.

You will also need to look at scalability. Is it a proven technology that you are buying? Some drives have been around for years and their manufacturers continue to provide us with helpful roadmaps. There are technologies like DDS, which are reliable and widely used that don't have any future roadmaps. Expanding these systems will require more hardware since an increase in capacity is unlikely to emerge.

9 tape drives tested. Read our independent review.

It is also important to evaluate your choice of backup software as there are many specific features that can enhance your backup process. Some of the more popular packages out there include Veritas Backup Exec, Veritas Net Backup (64 bit, High-End), Computer Associates, and ARCserve.

Let's look at the various tape formats.

Tape formats

LTO
Linear Tape-Open (LTO) is an open format technology that was jointly developed by HP, IBM, and Seagate. The "open format" means that tapes and drives from different manufacturers are compatible with each other.

LTO uses linear multi-channel bi-directional tape formats and includes enhancements in the areas of timing based servo (error correction), hardware data compression, and track layouts. There are two formats based on the LTO technology: Accelis and Ultrium.

The first generation of Ultrium allowed for storage of up to 100GB of data (>200GB compressed) on a single cartridge. The Accelis format utilises all the advantages of LTO except that the capacity has been reduced to improve access times to data.

Ultrium Generation 1: Capacity 100GB native, 200GB compressed; Transfer Rate 20 to 40MBps compressed.

Ultrium Generation 2: Capacity 200GB native, 400GB compressed; Transfer Rate 40 to 80MBps compressed.

Accelis Generation 1: Capacity 25GB native, 50GB compressed; Access Time < 10 sec, Transfer Rate 20 to 40MBps compressed.

DAT
DAT stands for Digital Audio Tape and was originally intended as a CD-quality audio format. In 1998, Sony and HP defined the DDS (Digital Data Storage) standard, transforming the format into one that could be used for computer data storage. DDS uses helical scanning to record data in much the same way a videotape recorder records data. The DDS protocol is represented by several standards, all of which are backward compatible.

DDS-1: Capacity 2GB native; transfer rate 0.55MBps.

DDS-2: Capacity 4GB native, 8GB compressed; transfer rate 1.1MBps compressed.

DDS-3: Capacity 12GB native, 24GB compressed. DDS-3 uses PRML (Partial Response Maximum Likelihood), which eliminates electronic noise; Transfer Rate 2.2MBps compressed.

DDS-4: Capacity 20GB native, 40GB compressed; transfer rate 4.8MBps compressed.

A DDS cartridge needs to be retired after 2000 passes or 100 full backups and every 24 hours you should clean your drive with a cleaning cartridge and discard the cleaning cartridge after 30 cleanings.

DDS tapes have an expected life of at least 10 years.

DLT
DLT is an adaptation of the old reel-to-reel magnetic recording method where the tape cartridge performs as one reel and the tape drive as the other. One of the most significant variants of DLT is Super DLT. Using a combination of optical and magnetic recording techniques known as Laser Guided Magnetic Recording (LGMR) Super DLT uses lasers to more precisely align the recording heads. It also makes it possible to store upwards of 100 GB on a single cartridge.

DLT 7000: Capacity 35GB native, 70GB compressed; transfer rate 20MBps compressed.

SDLT 220: Capacity 110GB native, 220GB compressed; transfer rate 22MBps compressed.

SDLT 220: Capacity 160GB native, 320GB compressed; transfer rate 32MBps compressed.

AIT
AIT (Advanced Intelligent Tape) uses a helical scanning technique, similar to that used in Mammoth drives. AIT incorporates IBM's Advanced Lossless Data Compression (ALDC) technology, which can offer an average data compression ratio of 2.6:1 across multiple data types. There are currently four generations of this format.

AIT-1: Capacity 35GB native, 90GB compressed; transfer rate 10MBps compressed .

AIT-2: Capacity 50GB native, 130GB compressed; transfer rate 15.6MBps compressed.

AIT-3: Capacity 100GB native, 260 compressed; transfer rate 31.2MBps compressed.

SAIT-1: Capacity 500GB native, 1.3TB compressed; transfer rate 78MBps compressed.

VXA
VXA, initially introduced by Ecrix, uses a variable speed to essentially match the speed of the tape to that of the host, thereby optimising tape drive performance and minimising undue stress on the media. The combination of Discrete Packet Format (DPF), variable tape speed operation, and an overscanning technique allows data to be read from any physical location on the tape, without having to follow tracks from beginning to end. There are two generations of this format currently available.

VXA-1: Capacity 33GB native, 66GB compressed; transfer rate 6MBps compressed

VXA-2: Capacity 80GB native, 160GB compressed; transfer rate 12MBps compressed.

Mammoth
Introduced in 1996, Mammoth is an advanced and reliable technology that represents Exabyte's response to the requirements of the mid-range server market. Mammoth features an Exabyte designed and manufactured deck and is specifically designed to improve reliability by reducing tape wear and tension variation.

Exabyte's Mammoth-2 drive uses a new multichannel helical scanning head, the latest error-correction algorithms and offers a 2.5:1 compression ratio using ALDC (Adaptive Lossless Data Compression).

Mammoth-1: Capacity 20GB native, 40GB compressed; transfer rate 6MBps compressed.

Mammoth-2: Capacity 60GB native, 150GB compressed; transfer rate 30MBps compressed.

Travan
Travan drives are a very simple and robust linear format with single channel recording and a simple tape path. There are a few generations of this format. The most recent of these is TR-5 (NS-20) and TR-7.

TR-5 (NS-20): Capacity 10GB native, 20GB compressed; transfer rate 1.83MBps compressed.

TR-7: Capacity 20GB native, 40GB compressed; transfer rate 4MBps compressed.

Automated backup
We have seen that there is a great variety of storage devices that can be used to back up your data, whether it's tape, disk, or DVD drives. When speed, capacity, and reliability come into the enterprise equation, however, most companies will be looking at one of the following automated tape storage applications that have emerged:

Tape libraries: With rapidly growing data capacities to consider to handle backup for client servers, many organisations opt for off-line data storage with automated access and control. A "tape library" is a high-capacity data storage system used to store, retrieve, read, and write data using multiple magnetic tape cartridges. Essentially, it is made up of two pieces of hardware: the tape drive itself plus the robotics used to manipulate the tapes. Robotic arms select tape cartridges from built-in storage racks and load them into the drive when required by the backup software. When the cartridges are full, or are no longer needed, the arm puts them back in the library. Tape library units may have several drives for simultaneous reading and writing and may hold from a few to hundreds of cartridges. Larger units can have hundreds of drives and store several thousand cartridges. These devices are referred to as "near online" devices because they are not as fast as on-line hard disks.

Tape arrays: Tape arrays are built around technology normally used with disk-based RAID subsystems. Arrays use special controllers that can stripe data across multiple drives in parallel, as opposed to the slower method of using sequential access on a single device. For extra fault tolerance, most tape arrays can be configured with a parity drive. The downside is a decrease in overall throughput gains.

Hierarchical storage management: HSM applications have been developed in an effort to minimise storage costs while optimising performance. They do this by combining multiple storage media such as magnetic disk, optical disk, and tape into a single logical unit, and transparently migrating data between media based on access frequency.

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