Musings on IT, data management, whitewater rafting, and backpacking

Tuesday, December 22, 2009

Tapes are not for long term storage

Tapes are much more energy efficient than even the best MAID disk storage system.

However, until you've had to recover data from tens of thousands of rotting tapes which need tape drives that are no longer manufactured -- don't talk to me about energy efficiency. We need to keep lots of digital data "forever", but we rarely get enough money to do that well.

I can tell many strange stories about tape rot and recovery, but one story is especially absurd.


We store 9-track tapes hanging by hooks from specially designed racks. Tapes have sticky labels so we can identify the contents. After a couple of decades, the glue no longer holds the labels onto the tapes. Every morning, we find piles of these labels on the floor, and unlabeled tapes on the racks. Most of these unlabeled tapes go straight to the recycle bin, because without the labels, the tapes are worthless.

Tape capacity is not keeping up with disk capacity. 2 TB 3.5 inch hard drives are smaller and almost as cheap as 800 GB (uncompressed) tapes. Moving data on and off tapes is much slower than disks.

BTW -- tape compression is almost useless. All of our space-hogging data, like images, video, and many scientific formats, are already compressed, and can't be recompressed, so we never see the 2:1 or even 2.5:1 compression ratios claimed by various tape vendors.

My disk versus tape philosophy goes something like this:
  • Tapes are easy to put away and ignore
  • Recovering data from old tapes is expensive, and easy to postpone ("next year")
  • Ignore old tapes long enough, and you lose the data
  • Big piles of spinning disks are hard to ignore.
  • Eventually disks fail and can't be ignored.
  • When disks fail, you replace them, move the data, and your data are safe for another few years.
Therefor:
  • Long term data storage is always on disks, because you are forced to deal with the data.
  • Disaster recovery storage can be on tapes, because after a year or so, the value for disaster recovery is almost zero.
  • Tapes have value for disaster recovery, data transfer, and other uses, so we will use tapes for the foreseeable future.
However:
  • Using disk drives or remote storage for disaster recovery could eliminate tapes. Just waiting for the cost to come down, and I need to get comfortable with shipping disk drives around. (Although, tape cartridges are getting more fragile with each redesign.)
And no, Amazon S3 and similar services are not cheap enough yet, both for Amazon's charges and the bandwidth.

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