Why Network Administrators Are Moving From Autoloaders to Tape Libraries
The basic idea of RAID was to combine multiple small, inexpensive disk drives into an array of disk drives which yields performance exceeding that of a Single Large Expensive Drive (SLED). Additionally, this array of drives appears to the computer as a single logical storage unit or drive.
The solution to this problem is the multi-drive automated tape library, combined with the new storage management applications, including concurrent backup and HSM (Hierarchical Storage Management). Automated tape libraries allow random access to large numbers of tape cartridges and concurrent use of two or more drives, rather than manually loading one tape after another or using a single-drive sequential autoloader.
The Move To "Lights Out Backup"
Network administrators industry-wide have recognized the need for automating the backup and restoration process to the extent that little or no human intervention is required. This has come to be known as "lights out backup." This process can be done off-shift, or concurrently with other applications during normal operations. Multi-drive tape libraries are the only available technology that offers both the flexibility and low cost to make lights out backup practical.
Hierarchical Storage Management Makes Data Flow More Efficient
Hierarchical Storage Management has emerged to address both the escalating cost of storage and the amount of data to be moved across limited network bandwidth. HSM allows network administrators to define parameters that cause automatic file migration from magnetic disk storage to less expensive alternatives, like tape. This migration can be based on any number of factors, but is typically triggered by the age of a file or how frequently it is accessed. Once files are migrated off the server onto tape cartridges, the system resources needed to manage them are substantially reduced. HSM applications range from simple disk grooming utilities to very complex enterprise-wide solutions that operate across heterogeneous networks and platforms. One thing is clear about the hardware required for effective HSM tape libraries are the ideal storage medium, while autoloaders do not have sufficient flexibility.
Tape Libraries vs. Autoloaders
Much confusion exists over the terminology used to describe tape automation products. However, the distinction is rather simple: Autoloaders have one tape drive, and are typically used to access a small number of tapes once a day. Most are designed for purely sequential operations. These units place no emphasis on performance.
Automated tape libraries always house two or more tape drives. All tapes are accessible to all drives, thus making concurrent reading and writing operations pOSSIble. Libraries always house more tapes than autoloaders. Throughput can be increased by adding additional drives. Libraries typically exchange tapes in eight seconds or less, substantially improving file restore response times. Tape libraries are mandatory for "lights out" operations and other higher performance tape storage applications. Tape libraries also offer the security of knowing that another drive will take over if one should fail.
Things To Look For In Selecting An Automated Tape Library
Beyond simply having two or more tape drives, tape libraries need a number of additional features to support the applications and duty cycles that today's network environments demand. When selecting an automated tape library, the following are some of the needs that a network administrator should address:
- Barcode Scanning: As tape inventories grow, barcode labeling becomes vital. Automatic barcode scanning substantially reduces the time it takes to inventory all of the tapes in a library. Without barcodes, each tape needs to be inserted into a drive, made ready, and the tape label information read. This process can take hours in large libraries, during which the tapes are not available to the network. Using barcode scanning reduces inventory time to less than two minutes.
- Expanded Capacity: Tape libraries allow several complete data sets to be kept available at all times. Small libraries can store 10 to 20 tapes; larger ones store over a hundred cartridges. These capacities mean that users are not restricted to restoring just the most recent version of a file, but can readily access previous generations, if necessary. Library capacities range from several dozen gigabytes to multiple terabytes.
- Multiple Drive Support: While even entry-level libraries provide all the benefits of at least two tape drives and library-based automation, larger models house four to six tape drives for much greater throughput and reliability. A single library can usually support multiple network servers. Multiple SCSI bus support can be readily implemented for even more powerful configurations.
- I/O Port: Complex applications, like concurrent backup and HSM, require control of the tape inventory housed within the library. I/O ports, commonly called "mailboxes," allow importing and exporting individual cartridges under application control, without any need for an operator to manually insert or remove media.
- Field Expandability: In addition to the storage growth factors mentioned above, many network administrators are being asked to secure the data resident on the desktops. Most tape library product lines offer models that can be easily expanded in the field to keep pace with new requirements.
Recent Advances In Reliability
As more networks operate around the clock, tape library reliability has been the focus of much development. Advanced robotic mechanisms have been introduced that can legitimately claim to operate for years without failures.
Much of this improvement has come from incorporating servo control systems that concurrently monitor all operations as they occur and provide constant feedback that allows the library to adjust its mechanical operations on the fly. Optical sensors rather than microswitches servo motors in place of stepper motors precision lead-screw mechanisms instead of belts and pulley and the introduction of self-aligning and auto-calibrating techniques have led to a five-fold improvement in reliability over previous generations. Unlike earlier tape automation products that required manual alignment of the drive to the robotics, today's designs treat the tape drives within the library as a plug-replaceable component that can be changed in less than one minute.
Tape libraries are usually used in environments that cannot tolerate any significant downtime. Systems running concurrent backup, or HSM, in particular, will not function without the library. This requires that on-site maintenance services be readily available to insure that service issues are dealt with quickly. National maintenance organizations such as IBM now offer support for the leading libraries.
Is The Size Of The Network Important?
With applications such as "lights out backup" and HSM, the size of the network doesn't dictate the need for an automated tape library. While the need for tape libraries in large networks is obvious, many smaller organizations are operating networks around the clock, with the same need for automation as larger enterprises. Libraries are available in a wide range of capacities and performance levels, to match just about any requirement.
Who Provides The Software?
Storage management applications are widely available from independent software developers such as Seagate, Cheyenne Software, Legato, PDC, Software Moguls, Wang Software and many others. Most applications have built-in support for a wide selection of libraries.
The cost of automated tape-based storage is under $.05 per megabyte, including drives and media. With the new higher capacity tape cartridges being announced this year, costs are sure to get lower. While very small, lower-performance networks may be adequately served by autoloaders, most network administrators are recognizing that the time has come to shift to automated tape libraries.
Qualstar is a leading manufacturer of automated cartridge tape libraries and other tape storage products. Qualstar's tape storage products are sold worldwide to OEM manufacturers, system integrators and resellers for use with networks, minicomputers, workstations and personal computers. Founded in 1984, the company is also a leading manufacturer of 9-track and 3480/90/90E tape drives for the desktop and workstation market.
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