• 11/22/2011
    8:25 AM
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The Tape Format Rot Fear Factor

As I speak with users at the backup seminars I teach around the country, I often hear them say that they avoid using tape for long-term data retention, expressing their concern with something like, "They come out with a new format every few years, and then you can't read your tapes." While it is technically true that, eventually you'll have to migrate data from old tapes to new media, and you should probably be able to go longer between migrations with tape than with disk archives.

Where disk array vendors practice 1950s-era planned obsolescence to get you to upgrade every five years, tape library vendors usually assume a longer service life for their products. As a result, it’s common to see users running 10 year old tape libraries, but rare to see 10-year-old disk arrays running in a data center.

Of course, vendor support policies vary. I’ve had vendors tell me that if I replace the LTO-1 drives in a library with new LTO-3 drives, the drives' warranty end date would be the library warranty end date, meaning there would be no warranty on drives put in a 7-year-old library. On the other hand, Spectra Logic has promised to provide service for libraries as long as it can get spare parts and not to raise its service rates beyond the rate of inflation.

Migrating data from one disk array to another is straightforward--just copy the files--but once you’re talking about tens of petabytes of data, nothing happens quickly. Transferring the contents of a typical midrange deduplicating target, like a DD690, DXi6700 or StoreOnce 4324 that holds 200 to 600 Tbytes of deduplicated data and can move data at 8 Tbytes per hour to a replacement, will take several days.

Transferring data from an old tape to a new one is a simple tape-copy command, but restacking data so the data from four LTO-5 tapes are consolidated on to a single LTO-7 is more complicated, as the archiving software has to be aware of the data’s new location. I’m looking forward to LTFS (LTO File System, a self-describing format for storing files on LTO-5 and later tapes) archive apps and libraries that can restack data automatically by policy.

Tape-format rot shouldn’t dissuade you from using tape for the long run. You’ll have to migrate data half as often as the disk folks if you implement every other LTO version. Next, we have to simplify the migration process.

Disclaimer: EMC and HP’s Storeonce group are clients of, Spectra Logic flew me to Boulder, bought me a few nice meals and drinks and worst of all made me think at their analyst’s day.

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