Article

Tape backup overview

Stephen J. Bigelow, WinIT
Tape is the quintessential backup technology, providing cost-effective, long-term data storage for all business types and sizes. Although tape performance is relatively

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slow, tape fits well into the storage architecture, because it allows users to store a large volume of data at a reasonable price.

Therefore tape technology is an ideal solution to protect the 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 media

Tape technology starts with the media -- the tape cartridges themselves. Tape is simply 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. Because tape cartridges are designed for specific tape drive architectures, such as Travan, digital data storage (DDS), digital linear tape (DLT) or linear tape open (LTO), they are not interchangeable. This is why tape systems must be selected for their technological longevity and media costs, which can make a company's tape storage strategy more expensive.

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When implementing a tape system, storage manaers must make adequate provisions 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 thousands of customers, so it's essential for storage administrators to track the delivery of tape media through trusted couriers. Firms such as Iron Mountain will pick up the tapes at your door; using general-purpose shippers has the potential for a security breach. If a security breach does occur, administrators should have a plan in place to mitigate risk and adhere to any legal reporting requirements. Organizations are opting to protect their data with encryption implemented in backup software or an in-line appliance. Encrypted data is generally regarded as being safe from loss or theft, and can limit the organization's liability.

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. By contrast, the LTO tapes are typically rated for 1 million passes (though many passes may be required for a single complete backup), sustain up to 20,000 loads/unloads, and retain data for up to 30 years.

Tape drives

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 SMBs.

  • 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. The new LTO-4 standard supports up to 1.6 TB of compressed storage at compressed data rates to 240 Mbps. Upcoming iterations of the LTO standard promise 3.2 TB capacities at 360 Mbps, and 6.4 TB capacities at 540 Mbps (all using compression). LTO-4 is also the first tape standard that incorporates encryption on the tape drive mechanism itself using 256 bit AES-GCM.

    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.

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    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 a storage staffer must be present to run the process unless the tape is embedded within an automation system.

    Tape maintenance issues can particularly be a problem for remote offices where personnel have little (if any) IT expertise. Ignoring 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. Today, remote offices are deploying remote backup technologies that will pass data from remote offices to a disk-based backup target at the corporate data center across a WAN.

    Tape libraries

    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. Tape library vendors include IBM, 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 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 and physical cartridge locations so the library can locate a specific file without a user needing to know which tape contains the necessary data.

    Backup applications

    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 back up 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.

    Some backup software will support encryption, protecting data at the backup server before sending the encrypted data off to the tape drive or library. 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.

    Selecting backup software 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.


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