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Is deduplication ratio an important backup consideration?

The deduplication ratio was once a point of vendor competition, but now this figure doesn’t carry the weight it used to. Learn why in this Expert Answer.

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Three or four years ago, there was something of a deduplication arms race going on. Vendors competed fiercely to achieve the highest possible deduplication ratio. Just as one vendor would advertise a 20:1 ratio, another would issue a press release stating it had achieved a 50:1 ratio.

Today, these figures are hardly even worth considering. For all practical purposes, vendor-advertised deduplication ratios have become meaningless for two main reasons:

  • When a vendor states it can achieve a 50:1 deduplication ratio, that number indicates a best-case situation. In the real world, deduplication ratios are often much lower than what vendors advertise as being possible. Remember, deduplication works by removing redundant data. If no redundant data exists, then deduplication is impossible. Some types of data are already compressed and therefore contain very little redundancy. This is especially true of media files such as MPEG videos or JPEG images.
  • As the ratio increases, the data deduplication process yields diminishing returns. For example, if you deduplicate 1 TB of data, a 2:1 deduplication ratio (which is very low) eliminates half the data (512 GB). By the time you get to a 20:1 ratio, 95% of the data has been eliminated and your 1 TB of data has been reduced to a mere 51.2 GB. If you increase the deduplication ratio to 25:1, there is not much more data that can be eliminated because most of the redundancy has been removed. Moving from a 20:1 to 25:1 ratio only reduces the data by another 1% and the data volume by approximately 10 GB, which is insignificant compared to the original 1 TB of data. The data reductions become increasingly insignificant as the deduplication ratios get larger.

Next Steps

Vendor deduplication ratio claims vary widely

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This was last published in October 2015

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How important is a deduplication ratio for your backup system?
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It's like the miles per gallon figure for a car -- your mileage may vary. And it seems to me if the data has already been deduped, buying a new dedupe product isn't going to help you any.
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Widespread collaboration might benefit from higher levels of deduplication. Given the size of working files, given the number of people who touch those files, duplicate information is everywhere. Even a tiny boost in data reduction may have a significant impact.
Even at that, there's a cost/benefit ratio to be explored here. No point in stronger dedupe if there's no profit in that tiny bit of extra space.
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