Tape vs. disk storage: Why isn’t tape dead yet?

Despite the many advantages of disk storage for backing up data, shipments of tape storage keep growing because for some jobs, tape is best.

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It might surprise some that despite the popularity of disk storage, the amount of data currently being placed on tape continues to rise.

For example, 2017 saw the shipment of more than 1 million petabytes in LTO tape capacity – roughly five times what was shipped in 2008. At the same time, the tapeless backup and recovery system has become the norm. Every backup expert that I know recommends disk as the primary target for backup and recovery.

How then to explain the increase in the amount of tape being shipped? The answer might be surprising, but first let's take a look at what tape is good at – and not so good at.

Tape is cheaper than disk

Even with all the advancements in deduplication – which is primarily used on disk – tape is still cheaper per gigabyte than tape for a few reasons. Tape allows you to separate the medium from the recording device, which allows you to buy a handful of tape drives and thousands of tapes. Those thousands of tapes also do not need power and cooling to maintain their data. In fact, some have suggested that even if disk was free it would still cost more than tape due to the power and cooling savings alone. The fact that tape is less expensive than the alternatives is the main reason were still talking about it.

Tape is better at writing data

When writing bits to storage, there is something called an unrecoverable bit error, which is when a device stores a one instead of zero or vice versa and it isn’t fixed with error correction. What many people do not understand about tape is that it actually has a better bit error rate than any other recording medium.

LTO-7/8 and Oracle T10000 tape drives both have unrecoverable bit error rates of 1:1019, which is roughly one error every 1.25 EB. Enterprise class disk drives have an error rate of 1:1015, or an error every 125 TB. That essentially means that tape is 1000 times better at writing ones and zeros than the best disk drive. (In case you're curious, SSDs range from 1:1016 to 1:1018, so tape is also 10 times better than SSDs

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