Monday, March 7, 2011

Which data storage media is more reliable, disk or tape?

If I was a gambling man I would bet that most if not all the responses to the question "Which data storage is more reliable, disk or tape?" would support the position that magnetic disk media more reliable than magnetic tape. If my assumption is correct then there will be many surprised expressions when I point out that it is magnetic tape that is the more reliable. To be clear I am not talking about older technologies such as early LTO, DLT, 4 and 8mm helical scan, but to the newer enterprise tape solutions such as the multi-vendor LTO-5 technology, Oracles recently announced T10000B and IBM’s TS1120/1130.

As pointed out by Fred Moore in his recent white Paper, “Tape: New Game, New Rules” bit error rates (BER) is becoming an increasingly popular measure of reliability. BER is a measurement of errors/total data stored or transmitted and is usually expressed as 1 in 10 to a negative power. For example a BER of 1x10E-8power means that for every 100,000,000 bits stored or transmitted no more than 1 bit will be in error.

So with bit error rates of 1x10E-17power for LTO and 1x10E-19power for the Oracle and IBM solutions these new tape formats have significantly passed magnetic disk which currently tops out in this critical measure of reliability performance at 1x10E-16power for enterprise class FC/SAS drives .

So why is BER so critical? Think about the increasing use of compression, data deduplication or encryption techniques. If data that has been transformed by one of those techniques contains one or more of these bit level errors then that data is likely non-recoverable.

So with a reliability advantage, an archival life advantage, a kW-hr/GB stored advantage and a $/GB advantage is tape positioned to challenge disk as the storage medium of choice for what is now becoming labeled as big data?

IBM, Oracle and Spectralogic are certainly bullish on the outlook for tape but one company that certainly does not think so is EMC. EMC suggested in their recent announcement that “Tape Sucks” and that the last bastion of tape application, deep archive, is ready to adopt disk based solutions. Their recent acquisition of Isilon and their investment in Atmos and the Data Domain Archiver are testaments to their commitment to disk technologies for mass storage solutions.


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