Storage is typically arranged in tiers based on the importance of the data and the speed of access and recovery. Long-term storage sits at the bottom layers of the corporate data-aging stack.
The data stack looks something like this: First is mainline storage, where your primary storage systems, SANs (storage-area networks) and the fastest, most reliable storage reside. This is the best place for data you need regularly and quickly, such as project files. Next is secondary storage, typically in the form of direct-attached server storage and special-purpose storage. Third is nearline storage, generally used for data aging and disk-to-disk backup. At the bottom of the stack are the tape backup drives and automation systems--the end of the line for many companies' data.
Some organizations have branches or secondary storage on this last storage stack, such as CD-ROM archival systems attached to the main array. Although this may have been an acceptable practice for expanding storage in the past, it's an inefficient data-storage method today. Adding branches adds complexity, which can cause confusion and errors in the backup process. All data should instead flow down the stack.
Tape is the most commonly used media for long-term storage. The main issues with tape storage, of course, are the time it takes to retrieve data and the reliability of the hardware used to access it. If stored properly, many modern magnetic tape formats have shelf lives of up to 30 years. That's improving, too: Sony is making write-once versions of the SAIT and AIT-3 tape technologies that provide permanent archival tapes. AIT-3 WORM (write-once, read-many) is shipping now, and SAIT WORM should ship soon. These tapes don't require special drives, so you can use your existing drive hardware if it's healthy.
It's a growing trend for tape formats to be backward-compatible, at least for read compatibility. Sony's AIT-1 tapes, for instance, can be read by the newer AIT-3 and AIT-2 drives. DLT, LTO and other tape formats are also providing backward-compatibility as tape-drive manufacturing companies, such as Hewlett-Packard, IBM, Quantum, Seagate, Sony and StorageTek have been listening to their customers' cries for backward compatibility.
Another long-term storage technology is optical, or magneto-optical, WORM storage. Hewlett-Packard, Plextor, Pioneer and Toshiba are the main suppliers of optical storage media and drives. HP offers high-capacity storage systems designed with 20- to 25-year backward-compatibility life spans.
There are also CD-R and DVD-writeable storage formats. CD-R, which is a write-once, read-many media, has a shelf life of only five years. Some DVD manufacturers claim 100 years for certain kinds of DVD media. DVD and similar technologies like the emerging blue laser initiatives, with higher capacity that reaches the 20 GB to 50 GB range, have made inroads in long-term storage with DVD-writeable jukeboxes (see "Pluses and Minuses of DVD Formats," page 86).
Meanwhile, beware of cobbled-together storage systems from unknown vendors that cram multiple, rewriteable DVD drives into a box. You need long-term service and support, so pin down your vendor on its upgrade and shelf-life claims. Your archival system should be something that's still readable down the line, so keep your storage equipment under a maintenance contract because once it can't be serviced anymore, your data is more or less dead. And don't sell yourself short by choosing a cheap solution for your long-term data archival system. Your long-term data is just too valuable.
Steven J. Schuchart Jr. covers storage and servers for Network Computing. Write to him at sschuchart@nwc.com.
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