Tape is the quintessential backup technology, providing cost-effective, long-term data storage for all business types and sizes. Although performance is relatively slow, tape fits well into the storage architecture allowing users to store a large volume of data at a reasonable price -- an ideal solution to protect the valuable data on traditionally more expensive hard disks.
Today, the falling cost of hard disk storage is causing many companies to opt for disk-based backup products offering much faster backup and recovery times. But tape remains a viable platform for many archival and disaster recovery applications. Tape technology starts with the media -- the tapes themselves. Simply put, tape is a long continuous ribbon of flexible plastic film coated with magnetic media. The tape is wrapped onto spindles and sealed in a specially designed mechanical cartridge that protects the tape from damage and dust. The media cartridge in a tape system is analogous to the spinning platters in a hard disk. Tape cartridges are inserted into a tape drive prior to use, and are later removed for transport and storage. Tape cartridges are designed for specific tape drive architectures (e.g., Travan, digital data storage (DDS), DLT or LTO) and are not interchangeable, so tape systems must be selected for their technological longevity and media costs, which can add significant cost to a tape storage strategy.
When implementing a tape system, adequate provisions must be made for tape storage. Smaller organizations frequently vault a limited number of tapes in a fireproof safe on site or at a local storage facility. Larger corporations can use many tapes for long-term archival backups and disaster planning, so they are routinely shipped to off-site storage facilities run by firms like Iron Mountain Inc. The largest enterprises may ultimately collect tens of thousands of tapes. Lost or stolen tapes may compromise the personal data of many thousands of customers, so it's essential for storage administrators to track the safe and timely delivery of tape media through trusted couriers. Firms like Iron Mountain will pick up the tapes at your door; using general-purpose shippers can potentially open the door for a security breach. If a security breach does occur, administrators should have an action plan in place to mitigate risk and adhere to any legal reporting requirements.
Finally, tape doesn't last forever, so administrators must consider cartridge lifecycle management. Wear on the mechanical assembly and tape media itself will limit the cartridge's working life. For example, a typical DDS cartridge is rated for 2,000 passes (over the tape drive's read/write head) or 100 full backups -- after which the cartridge should be securely destroyed. Tape data degrades slowly over time once written, so administrators must also plan to periodically rewrite (refresh) aging tape data to ensure continued integrity. DDS tapes are rated for a life expectancy of 10 years or more.
A tape drive is the electromechanical device that reads and writes to the tape cartridge, and exchanges that data with the rest of the computer. Drives typically use either helical scan or linear tape head technology to access the tape. Helical scan drives use a rotating head positioned at an angle, reading and writing data as diagonal stripes along the tape's width. Linear tape simply positions a stationary head that runs along the tape length. There are numerous tape formats in service today that leverage these two approaches, and the choice of tape drive should include a consideration of capacity need, performance speed, media cost and technological longevity.
Advanced intelligent tape (AIT). This helical head technology was designed to record computer data on 8mm tape cartridges. AIT cartridges can support up to 400 GB with compression, and drives can transfer data up to 48 Mbps (also with compression).
Digital data storage (DDS). This helical head technology was designed to record computer data on 4mm digital audio tape (DAT) cartridges. There are five generations of DDS format capable of saving 2 GB, 8 GB, 24 GB or 36 GB or 72 GB to a DAT cartridge. Fairly small storage capacities make DDS technology better suited to small and mid-sized businesses.
Digital linear tape (DLT). This linear head technology records data along a series of 128 or 1280 data tracks. DLZ1 compression helps to fit more data on the tape, and increase the effective read/write speed. Ordinary DLT cartridges can hold up to 160 GB of uncompressed data, though SuperDLT (DLT-S) cartridges can support to 800 GB of uncompressed data. DLT drives can run up to 60 Mbps.
Linear Tape-Open (LTO). This open-standard linear tape technology has evolved through several generations, currently supporting enterprise-class storage capacities to 400 GB of uncompressed data with transfer rates of 80 Mbps (up to 160 Mbps compressed). Upcoming iterations of the LTO standard promise 1.6 TB capacities at 240 Mbps, 3.2 TB capacities at 360 Mbps, and 6.4 TB capacities at 540 Mbps (all using compression).
Travan. This enterprise-class helical tape format was standardized by the Quarter Inch Cartridge (QIC) Consortium, and offers several iterations over its life. The latest capacities include 20 GB and 40 GB (compressed) storage capacities.
Storage Learning On-The Go Download this overview and listen on your iPod or laptop. Unlike hard disks and optical drives, tape drives require routine maintenance. Tape media comes into contact with the drive's read/write heads, so the heads must be cleaned periodically to prevent accumulations of residual magnetic material from causing read/write problems. A head cleaning cartridge will handle this task, though personnel must be present to run the process unless the tape is embedded within an automation system. However, maintenance issues can be problematic for remote offices where personnel have little (if any) IT expertise. Ignored maintenance can eventually result in backup problems. Remote tape systems should receive particular attention from storage administrators to ensure that any required procedures are performed in a timely fashion.
Of course, a tape drive can only hold one tape at a time and a single tape is unlikely to hold the complete backup of an entire organization. There are generally two options when more tape storage capacity is required: manually insert a new tape when the previous tape is full or utilize multiple drives organized into tape library systems. By making multiple drives available, backups can automatically "span" across two or more tapes as needed without human intervention.
There are numerous tape library vendors, including Quantum Corp., Hewlett-Packard Co., Tandberg Data and Spectra Logic Corp. In many cases, just grouping tape drives into a single system isn't enough -- tapes still must be inserted and removed manually. One way to further extend the potential storage capacity of tape systems, and reduce human error, is to use tape libraries with autoloaders. An autoloader is basically a robotic mechanism that can select a tape, insert it into a drive in the library, remove a tape that's been written and return the tape to a storage location. Such libraries often include management utilities that keep track of tape directories so the library can locate a specific file without a user needing to know which tape contains the necessary data.
Application software plays a huge role in any backup strategy. Backup software is a critical management tool that interfaces backup hardware with corporate data, allowing administrators to decide when and where to backup selected files, folders, drives, servers or even entire data centers. Backup software also supports automation so backups can be performed and verified on a preset schedule (e.g. nights or weekends) without direct human intervention. Most contemporary enterprise backup tools can easily send pager and e-mail alarms to a technician or administrator in the event of a backup problem. EMC Legato and Symantec Veritas are two well-known backup tools, though vendors offer numerous products to meet a wide range of business needs and budgets. Consequently, backup software selection isn't just an issue of price. Hardware compatibility, management features, automation capabilities and even service/maintenance agreements should be included in any product evaluation. ***