What you will learn: How to estimate the lifespan of LTO tape. It's not as black and white as LTO tape manufacturers want you to believe.
LTO tape lifespan can mean two different things. Unfortunately, neither kind of lifespan results in nice simple numbers. However, if you are aware of the lifespan characteristics of LTO tapes you can estimate when they need to be replaced.
You'll need to know what kind of LTO tape you're using. There are four generations of LTO tape: LTO-1 through LTO-4. Whereas LTO-2 amnd LTO-3 doubled the capacity and speed of the previous generation, the recently released LTO-4 only increased speed by 50%.
LTO generations
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LTO-1
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LTO-2
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LTO-3
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LTO-4
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Introduced
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2000
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2002
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2005
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2007
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Capacity
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100 GB
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200 GB
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400 GB
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800 GB
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Speed
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20 MBps
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40 MBps
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80 MBps
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120 MBps
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The lifespan of data stored on LTO tape is usually quoted as 30 years. However, tape is extremely sensitive to storage conditions, and the life expectancy numbers cited by tape manufacturers assume ideal storage conditions -- a constant temperature of about 70 degrees Fahrenheit and 40% relative humidity.
What's more, tape lifespan is "peaky." It doesn't take much deviation from those ideal conditions to produce big decreases in life expectancy. Even a 5 degree increase in storage temperature starts to cut life expectancy. High temperature, high humidity and high-light levels make tapes deteriorate much more quickly.
The other way to look at lifespan is how many times you can safely use the tape. Again, there are theoretical numbers and there's reality.
Use is usually quoted in terms of passes -- the number of times the tape passes over the heads. This can be misleading with tape technologies like LTO, which use a serpentine recording path. For example, LTO-2 and LTO-3 pass the tape over the heads 64 times to completely read a cartridge. Thus, a tape rated for 1 million passes (standard for LTO tapes) is good for 15,625 complete reads.
Dust is the great enemy of all kinds of tape. Even a little dust getting into the tape cartridge can significantly cut the number of uses. That is one reason it is important to unload LTO tapes from the drives when not in use. When the tape is in the drive, the shutter is open, making it easier for dust to penetrate.
There is also the matter of obsolescence. The LTO specification, introduced in 1999, calls for an LTO drive to be able to read tapes two generations back. Thus, the current LTO-3 drives will read LTO-1 tapes, but the new LTO-4 won't read anything earlier than LTO-2.
In many enterprises, obsolescence is a bigger problem than storage life expectancy. Keeping data on tapes that cannot be read by the current generation of drives puts you at the mercy of legacy drives. If your legacy drive fails, you're going to have to hunt to find another to be able to restore your data. For that reason, it may make sense to replace LTO-1 tapes in the next year or so, even though they have another couple of decades of life expectancy.
The other question for storage administrators is how far to push it. Since the purpose of tape storage is to make sure data is secure, you probably don't want to take tape lifespan (in either sense) to the theoretical limits.
Fundamentally, any tape is a consumable commodity. You should plan to replace it regularly and budget accordingly.
About the author: Rick Cook specializes in writing about issues related to storage and storage management.
