Backup targets: Tape libraries and VTLs

Tape drives, tape libraries and virtual tape libraries are among the popular backup target options available today.

Over the last several years, data backups have evolved to the point that they are hardly recognizable. For many organizations, the days of producing a nightly backup to tape are long gone. Factors such as exponential data growth and the need for near real-time data protection have driven organizations to abandon legacy backups in favor of next-generation disk-based solutions.

This primer on backup will explore backup hardware, common backup challenges and backup software today.

Tape drives/tape libraries

Tape drives have been the de facto standard backup target for decades. Although the drives themselves have evolved over time to become more feature rich and reliable, the basic concept of writing data to magnetic media has not changed.

Tape libraries vary widely with regard to their cost and level of sophistication. At its simplest, a tape library consists of a tape drive, a multi-tape magazine, and an autoloader. For example, the HP MSL2024 Ultrium 3000 tape library is a rack mountable unit that features a single LTO-4, LTO-5 or LTO-6 tape drive that can accommodate up to 24 tapes for a total device capacity of 36 TB (uncompressed). It's also worth noting that if LTO-6 is used, the uncompressed capacity is 60 TB. Some tape libraries feature multiple tape drives, robotic loaders and use bar codes to track tapes.

In spite of the fact that modern backups tend not to be tape-based, tape is not obsolete.

Even large enterprises still use tape libraries, though not as a primary backup mechanism. Instead, tape libraries are often used as a secondary backup target. Data is backed up first to disk and then later to tape in what is known as a disk-to-disk-to-tape architecture.

Some enterprise environments also use tape as a secondary storage tier. In this architecture, data is backed up to disk, but as that data ages, software automatically moves the data from disk to tape. Doing so allows aging data to be archived and frees up disk capacity for new data.

Virtual tape libraries

The best way to think of a virtual tape library is as a backup storage abstraction technology. That's a fancy way of saying that a virtual tape library is designed to make disk-based storage appear to the backup software as if it were a tape library.

The reason why virtual tape libraries were so important (and to some extent still are) is because they act as a mechanism to ease the transition to disk-based backup targets.

When it comes to backup targets, disk offers a number of advantages over tape. Disk-based targets offer faster backups and restores and facilitate more frequent backups. For a long time, however, backup software tended to not directly support the use of disk-based backup targets. Virtual tape libraries solved this problem by allowing disk-based storage arrays to masquerade as tape libraries, thereby making it easy to use the disk-based target with existing backup software.

Although virtual tape libraries are still used today, they are not quite as essential as they once were. It has become common for backup software to offer native support for disk-based backup targets. This is especially true of network-attached storage that is accessible through the CIFS or NFS protocols. 


This was first published in February 2014

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