Mixed media libraries make economic sense: how it's done is the differentiator. (Automated Storage Management).
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.
* Different physical interfaces: Multiple connection points for virtual partitions might include one pool connecting to a SAN through a Fibre Channel interface, and another pool attaching to the data network over IP.
Mixed media is one use for virtual partitions. Libraries essentially identify themselves to the backup software application, such as: "I am a device that is a pool of tapes, with its own characteristics. I have 300 AIT2 tapes, with the following capacity..." Perfectly straightforward, and the backup application proceeds to deal with configuration. But since backup applications need to deal with tape pools of exactly the same type of drive and media, different tape drive and media types within the same library will stump them.
In this case, library services will take one library and present it as several smaller virtual libraries, each presenting several different pools of differing characteristics. For example, the customer may have 600 tapes of Generation X, then when Generation Y comes along they can adopt a few new drives and create a separate partition for them in the library. As time goes on and they replace more and more of the older tape drives with the new, the Generation X partition shrinks while its resources are allocated to Generation Y, and that logical partition grows. A couple of years into the migration, IT retires Generation X and the library is completely Generation Y Nick Harper, vice president of business development at SpectraLogic pointed out, "The backup applications, and even the operating systems themselves, want it all to be 'mine.' Since everything they see they want, don't let them see certain things."
Library vendors using virtual partitions generally add this capability to their higher-end libraries, since it's associated with higher-level management issues usually reserved for costlier, enterprise-class libraries. In this scenario there is an entry hurdle to mixed media, a scale to achieve where it makes sense. At entry level, according to ADIC, small library segments of 20, 40, or 60 slots do not present a good economic case for virtual-partition-based mixed media. Instead of setting up virtual partitions in the smaller libraries, ADIC suggests buying 20 to 60 new LTO tape drives and make the switch rather than dealing with the backup applications' requirements for mixed media and creating the virtual storage pools in the mixed media library. Larger libraries present a better economic justification for mixed media, since the iT departments of large companies usually have more specialized procedures and more formal tape management infrastructures in place. ADIC and SpectraLogic do not anticipate seeing v irtual partitioned mixed media in lower-end markets, and do not plan to develop for it.
StorageTek approaches mixed media differently. Although it makes extensive use of virtual partitions in their libraries, it does not use it for mixed-media capability. Instead it developed native mixedmedia capabilities on all its libraries, including its smallest: a 4U height, 10-cartridge library. Ian Stewart, director of product marketing for automated tape solutions at StorageTek explained, "We offer mixed media in just about all of the libraries that we have in our portfolio. From our perspective, it is not a more expensive solution." He agrees that customers don't need mixed media capability every day, but he added, "With mixed media, it is more a capability that offers you some significant investment protection, but it is not a capability that is necessarily exercised by customers all that often. But they should have it if they want it. The mixed media is something we feel is important, and is integral throughout the product line."
StorageTek sees end-user customers wanting to try out drive types, for example deciding between DLT and LTO. Market confusion surrounding the drive types became less important when customers could run both in the same library. Stewart said, "It's that flexibility and investment protection that is the primary driver." In StorageTek's technology, drives and cartridges form one large matrix that can manage sub-matrixes. The library identifies and labels its cartridges and types, then maps them to particular drives. When the library receives a media request from an application, it mounts the appropriate cartridge to the correct drive. This happens regardless of the backup application's capabilities: If the backup application can intelligently choose its own tape drives, there is no conflict, but if not, the library can do it at its own level.
Mark Lewis, StorageTek senior product marketing manager says that although S torageTek offers advanced virtual partition capability, using virtual partitions for mixed media is awkward and time consuming. IT administrators must manually reallocate data between partitions as the drive types and media change. "You don't have to think about that. If you have extra slots and capability, they're dynamically allocated back and forth," he said. Dispensing with partition balancing makes handling mixed media a simpler exercise.
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|Author:||Chudnow, Christine Taylor|
|Publication:||Computer Technology Review|
|Date:||Sep 1, 2002|
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