Tape libraries

Midrange tape libraries have added sophisticated features such as partitioning to fend off the challenge of disk-based backup systems. With these new capabilities, tape libraries are finally assuming the role they were originally designed for: the long-term protection and preservation of data.

This feature, focusing on tape libraries, first appeared in the March issue of Storage magazine.


With disk systems taking on a more prominent role for backup operations, tape libraries are adding new features to become the medium of choice for long-term archiving.

Consolidation, centralized protection of remote-office data and longer data retention rates -- coupled with 50% year-over-year data growth -- are forcing organizations to use tape libraries in new or expanded roles. Tape library vendors are adding new features to their products to
Midrange tape libraries

Click here for a comprehensive list of Midrange tape libraries (PDF).

Tech Report library

remain relevant in this era of cheap disk, where disk-to-disk-to-tape (D2D2T) and virtual tape libraries (VTLs) are taking on larger backup and recovery roles.

A maturing class of midrange tape libraries (see What's a 'midrange' tape library? below) fills the gap between auto tape-drive loaders and high-end tape libraries that support hundreds of tape drives and thousands of tapes. These new midrange tape libraries allow organizations to either consolidate multiple auto tape loaders or to start small and scale to accommodate growth.

Features found in this class of tape libraries include:

  • Partitioning
  • One-frame configurations with support for up to 24 tape drives and 1,000 tape slots
  • Various licensing options to accommodate additional tape slots
  • Support for multiple tape media types
Midrange tape libraries' support for virtual tape

ADIC Scalar i500 integrates with ADIC's Pathlight VX 450 and Pathlight VX 650 disk-based backup systems.

Hewlett-Packard (HP) EML E-Series and ESL E-Series integrate with disk-based HP StorageWorks 6000 Virtual Library System.

Spectra Logic Spectra T950 offers native virtual tape support, presenting an LTO image.

Sun/StorageTek L700e will provide virtual tape support with Virtual Storage Manager Open, due to be released in the second half of 2006.

The adoption of low-cost disk hasn't signaled the demise of tape libraries, as many industry watchers predicted. Though disk in its various forms--disk volumes, disk cache and VTLs--is becoming the primary target for backing up data and the initial source for data recoveries, tape still often serves as the final resting place for corporate data. With unlimited capacity, low cost-per-gigabyte and portability, tape remains the preferred method for long-term data storage. But as organizations consolidate and share storage resources like tape libraries, business units tend to want to pay only for their portion of total tape library costs while retaining control of the data and tapes on which it resides.

The new Scalar i500 from Advanced Digital Information Corp. (ADIC), Redmond, WA, reflects how one vendor is responding to new user demands. The Scalar i500 scales from one to 18 LTO drives and 36 to 404 tape slots in a single frame, and includes partitioning as a default feature. Partitioning lets departments control specific physical resources within the i500 and treat them as if they were a separate tape library.

Partitioning makes chargebacks easier, too, with each user or department paying only for the tape drives, cartridges and slots they use even though they're all housed in the same physical tape library. Partitions let departments control how their tape library resources are used and keep their data logically and physically separate from other departments' data. IBM Corp.'s TS3310, Qualstar Corp.'s TLS series and Sony Electronics Inc.'s CSM200 are other examples of libraries that include partitioning as a standard feature.

Tighter integration with virtual tape and support for mixed tape media are other ways tape vendors are trying to make their products easier to use and indispensable for long-term archiving. And while data encryption isn't yet natively available, users are pressuring vendors to develop methods to encrypt data without sacrificing their ability to easily recover and read the data.

What's a 'midrange' tape library?

The lines defining tape library categories are blurring and, not surprisingly, vendors disagree on where to draw those lines. For example, Hewlett-Packard Co., Qualstar Corp. and Sony Electronics Inc. call their respective ESL series, TLS series and CSM series tape libraries enterprise products, while comparable models from Advanced Digital Information Corp. (ADIC), IBM Corp. and Storage Technology Corp. (StorageTek, now owned by Sun Microsystems Inc.) are considered midrange by those vendors.

The extremes are fairly easy to classify. Units like ADIC's Scalar 24 or Dell Inc.'s PowerVault 132T each support a maximum of two tape drives and 20 to 40 tape cartridges, which clearly places them in the entry-level class. Conversely, tape libraries like ADIC's Scalar 10K, IBM's 3484 and StorageTek's StreamLine SL8500 plainly belong at the high end of the spectrum because they support hundreds of tape drives and thousands of tape cartridges. But when tape libraries fall in between those extremes, the library classifications become hazy.

For instance, the differences among tape libraries like ADIC's Scalar 100, IBM's TS3310 and Sony's CSM100 are slight. ADIC's Scalar 100 offers some midrange features like support for either LTO or SDLT tape media and up to six tape drives. But tape library vendors tend to agree that capacity, not features, is the ultimate criteria when distinguishing between tape library classes. For the purposes of this article, the Scalar 100, with its support for a maximum of 72 cartridges, falls a bit short of our definition of a midrange library.

As a general rule, tape libraries can be classified based on the following capacity criteria:

-Entry level: Supports one or two tape drives, and fewer than 50 tape slots

-Midrange: Supports three to 11 tape drives, and 50 to 200 tape slots

-Enterprise: Supports 12 or more tape drives, and more than 200 tape slots

Partitions and scaling
Responding to requirements such as tape library consolidation, ease of expansion, uncomplicated cost allocation and support for different backup apps, nearly every tape library vendor offers partitioning.

While there's no magic formula for determining how many partitions an administrator should create within a library, less is usually better. For instance, Qualstar recommends that users keep its TLS series libraries in a single library configuration for a single host running a library-specific backup app. When multiple hosts are present, and each needs to run its own library-specific backup app, Qualstar suggests subdividing the TLS into as many as four smaller logical libraries.

Tape libraries vary in how they implement, scale and license partitioning. For all libraries, each partition must include at least one tape drive, and each tape drive may only be a member of one partition. Tape libraries like IBM's TS3310 support a partition for each tape drive in the library, up to its maximum of six tape drives. Others, like Quantum Corp.'s PX720, offer more tape drives (20) than partitions (six), which gives users more flexibility to mix and match multiple tape drives and slots within a partition. Overland Storage Inc.'s NEO 8000 only permits a second partition if another partition controller card is added to the unit.

Partitions may include as few or as many tape slots as the administrator defines, but tape libraries differ significantly in how they deliver and license tape slots. Sun Microsystems Inc.'s L1400M ships with all of the slots installed in the frame; Sun then sells customers access to the slots. The L1400M's default capacity of 200 slots is included in the base price of the library. Additional slots can be purchased in 100-slot increments, with a software key granting access to the slots. Spectra Logic's Spectra T950 library similarly delivers all of the tape slots in a single frame, but allows users to license additional slots in increments of 10.

ADIC uses an alternative approach with its Scalar i500. The Scalar i500 is available in three base configurations: 5U (control module with 36 slots), 14U (36, 82 or 128 slots) and 23U (82, 128, 174 or 220 slots). It's then physically scaled by adding 9U expansion modules above or below the base system, with all modules served by a single, continuous robotics system that eliminates the need for pass-through ports or elevator systems. Additional slots may be activated in 46-slot increments using a software license key.

Spectra Logic is the only vendor to mix disk and tape in its midrange library. The Spectra T950 library uses Spectra Logic's proprietary RXT SabreDrive and SabreMedia disk drives, which have the same physical shape as an LTO tape drive and tape, and present an LTO image to backup apps. The SabreDrive uses an internal RAID controller to write to the SabreMedia module, which holds multiple serial ATA (SATA) disks. SabreMedia offers the same portability as tape; users can specify the RAID level of the media when they order it. This approach also circumvents the issues with the bar codes normally associated with disk. The SabreMedia cartridge lets the tape library assign a bar code to it and treat it as any other tape cartridge.

Hewlett-Packard (HP) Co. and Sun are the only other vendors with tape libraries in this class that support the migration of virtual volumes to tape. But for users to gain this functionality from HP's Enterprise Systems Library/Enterprise Modular Library (ESL/EML) series or Sun's L700e libraries, they'll first have to place one of these vendors' VTLs in front of their tape libraries. HP users will need HP's StorageWorks Virtual Library System (VLS) 6000, while Sun shops will need to wait until the latter half of 2006 before they can use the firm's Virtual Storage Manager (VSM) Open in front of the L700e.

Where should encryption reside?
With stories of lost tape media regularly making headlines, Dave Kenyon, Sun's director of enterprise tape automation, says, "encryption is the killer app for tape." But questions remain about the role tape libraries should play in the management of encrypted data, or if they should play any role at all.

The need to encrypt data stored on tape is becoming a given, more for political rather than technical reasons. "There is no knowledge of where anyone has read data from a lost tape," says Molly Rector, Spectra Logic's director of technical marketing. "Yet publicly traded companies must make public announcements when a tape is lost. Encrypting data on the tape would prevent companies from having to make this announcement, thereby saving them face."

The two main questions in this debate are what device or application should do the encryption and how the keys should be managed. Tape library vendors mostly agree that encryption belongs in the tape drive. While backup software products like Symantec Corp.'s NetBackup offer encryption as an option, this approach unnecessarily locks users into a specific application and requires that application to be available before data can be decrypted and restored.

Allowing the tape drive to perform encryption has a number of benefits. It largely removes the potentially proprietary nature of encrypted data if the encryption is done by the backup software. Tape drives aren't proprietary to specific tape libraries; a tape encrypted by an LTO tape drive in a Quantum PX720 can be read by an LTO tape drive in an ADIC Scalar i500. And if the tape drive performs the encryption, it offloads the CPU overhead of encrypting the data from the backup server.

Spectra Logic offers an option to handle the CPU overhead created by the encryption process, which takes place outside of the tape library. The optional Quad Interface Processor (QIP) module for its Spectra T950 library acts as a switch between the SAN-attached Fibre Channel (FC) port and internal FC tape drive. This module handles the processing associated with encryption. Whether other tape library vendors will offer a similar module is questionable at this time. Some tape vendors appear to be waiting to see how market leader Sun handles encryption in its forthcoming Titanium E-10000 tape drive due in September.

While most tape library vendors agree that tape drives should manage the encryption, they have no solid answer for the larger question as to what application should manage the encryption keys. Whether this ends up being the responsibility of the backup software, some software provided by the tape library vendor or even a third-party application from a vendor like VeriSign Inc. remains to be seen.

Midrange tape libraries: Backup software support
Click here for a comprehensive list of support backup software products for Midrange tape libraries (PDF).
Fading features
As features like encryption begin to take center stage, other features, like multiple tape media support, high availability and large numbers of tape drives, are taking a back seat. A single library supporting multiple types of tape media and drives isn't as appealing to users as was first thought. According to Gartner Inc., LTO tape drives captured as much as 77% of the market in 2004, effectively establishing LTO as the default standard for tape.

ADIC's and Overland Storage's sales numbers back Gartner's statistics, as each reports that more than 75% of its new tape library sales contain only LTO tape drives. Tape libraries that support mixed media remain relevant for those users who need to manage or consolidate old tapes, such as SAIT or SDLT tapes.

High availability and high tape-drive counts also lack some of the luster they used to have. With disk becoming the primary target for backups and restores, users are more tolerant of tape library downtime for repairs and upgrades. Similarly, the ability to support a large number of tape drives is less important because the latest LTO-3 drives support higher throughput (80MB/sec uncompressed) on higher capacity tape cartridges (400GB of uncompressed data). Again, with disk becoming the initial target, data can be streamed faster to a fewer number of tape drives and cartridges over longer periods of time.

Tape libraries are finally assuming the role they were originally designed for: the long-term protection and preservation of data. With varying degrees of flexibility in configuring partitions and the new de facto standard of LTO, tape libraries are well positioned to fill this role. But as disk assumes its new role as the initial target for backups and source for restores, tape library vendors need to shore up their abilities to interact with disk libraries and provide users with some definitive answers on encryption.

About the author:
Jerome M. Wendt is a storage analyst specializing in the field of open-systems storage and SANs. He has managed storage for small- and large-sized organizations in this capacity.

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