I've been tasked with finding and implementing an HSM solution that we can integrate into our existing SAN. About two-thirds of the data will be moved offline almost immediately, but we expect the rest to be used with some frequency. Once data is moved offline, it will be stored for seven years before being destroyed so rewriteable media is not in my opinion necessary.
Due to the volume of data (I expect to write 100+ GB/month), the high media cost of WORM media removes it as an option, leaving me to consider CD, DVD and tape.
My first instinct was to use DVD, but all the DVD libraries I've seen utilize DVD-RAM that appears to be losing momentum in the marketplace. Also, DVD seems to be the slowest solution.
Tape seems to be fastest but tape libraries are three to four times as expensive as others, plus isn't tape a bad idea if you expect lots of reads over time? Or is that a myth?
AIT tape devices may fit the bill for you, since they can store the index information for very fast access to files during read access. AIT tape libraries can also be expensive though, but they store massive amounts of data. Check with a few vendors for pricing on AIT-2 or AIT-3 tapes.
The other solution may be a virtual tape device that uses inexpensive serial ATA disks instead of tape. The disks look to your HSM software as if it were any kind of tape format you need to write but it happens VERY fast.
Seven years is a long time though and keeping disks spinning for seven years may be more than you could ask from a particular solution. Although DVD may be slow, it may be the most cost effective solution for you at this point. The newer DVD drives will be able to work across multiple formats. I would buy some spare parts at the time of purchase, so if you have a problem 6.5 years from now you can still get at your data.
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This was first published in January 2003