Mixed media libraries make economic sense: how it's done is the differentiator - Automated Storage Management

Computer Technology Review, Sept, 2002 by Christine Taylor Chudnow

Mixing media in libraries means combining different generations of the same tape drive family, or even mixing multiple vendor tape drives of similar size and cartridge types. Most mixed media, accepts half-inch drives such as DLT and LTO. Mixed media, can help protect library investments, since libraries, media, and underlying drive technologies have different development cycles. Tape drive manufacturers generally introduce new generations every two and a half years, but library generations are closer to five to seven years. This means that libraries typically have economic and generational lives much longer than the underlying tape drives. Without mixedmedia capabilities, any time a customer upgraded or changed tape drives they would have to replace the drives in the entire library, or replace the library itself with a new one containing the desired drive type. This may be an acceptable alternative with a three-year-old, 10-slot library, but is hardly a good idea with a large library containing hundreds of t ape drives. The ability to mix and match similar drive types makes a compelling argument for shared library services and mixed media.

Tape drive upgrade paths and vendor migrations are not the only drivers for wanting to mix media in libraries. Nearline usage is becoming more common and compelling. In a near-line scenario, users retrieve active data from primary storage's fast disk. Data begins to age from its creation date, but as users continue to access it, an HSM (hierarchical storage management) application migrates it to a networked library-perhaps to a high-performance tape drive such as a StorageTek 9840. As data ages still further, HSM migrates within the same library to a lower-performance, high capacity drive such as LTO or DLT. This keeps great volumes of data easily accessible to users at all times without overloading primary storage or requiring expensive disk purchases for less active data.

Another driver for mixed media is legal requirements for accessible data. Financial industries, for example, will keep required records on tapes from yesterday's backup, tapes from three years ago, and tapes from seven to 10 years ago. Although the older data need not stay on fast disk, it should be easily accessible. A mixedmedia library can house the newest generation of tape drives along with older and legacy devices.

Steve Whitner, director of marketing at ADIC, believes that the primary use of mixed media is in transitional events. "In most cases what people are trying to do is to migrate from one media type to another," he said. "The reality is, they almost always have something that's running the old media type. The migration of going from one type to another is a point-intime event, it's not something they want to continue for a long time. They want to do it once, then be operating in the new media type."

In such a scenario, customers might deploy a newer library and leave an older library to serve legacy drives, or slowly take out the first library as they replace, migrate, or update the legacy applications. There can be a lot of money at stake: Large libraries easily cost more than $100,000, and in libraries with 1,000 or more slots, the cost of the media to fill the library can rival the cost of the library itself. To justify that sort of expenditure, companies need to make good use of the tape media. Whitner said, "Companies don't very often want to sustain both types of media over a long period of time. It's rarely worthwhile for them to invest in two technologies along parallel paths. It tends to be a more important factor for larger systems than smaller ones. The dollars become large enough that people can take on a larger management burden."

Different Approaches, Different Philosophies

Library manufacturers have different philosophies about including mixed-media capabilities in their libraries, depending on their particular technical approach. Companies such as ADIC and SpectraLogic, for example, handle mixed media (or shared library services) using virtual partitions, while Storage Tek uses a native app- roach. Predictably, they differ over the role of mixed media.

Partitioning libraries into logical volumes is one way of managing mixed media, though virtual partitioning offers far more advantages, including:

* Departmental allocation: Logical partitions by department allows different departments to use tape drive types and media that best suit their applications, as well as using their optimal backup software.

* Application allocation: Many applications prefer their own optimized storage pools, but many companies prefer not to adopt huge numbers of smaller libraries. It can be more economical to adopt larger libraries and make virtual partitions for applications.

* SSPs (shared service providers): Although the SSP business model is struggling, virtualized libraries proved to be an excellent model for sharing data, with different virtual pools dedicated to different customers.