LTO-5 tape is slated to be released later this year, with nearly double the capacity of its predecessor LTO-4. W. Curtis Preston, TechTarget executive editor and independent backup expert, outlines how LTO tape differs from other tape media, discusses the various generations of LTO tape, and the pros and cons of LTO in this Q&A. His answers are also available as an mp3 below.
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Table of contents:
>>How does LTO tape technology differ from other tape media?
>>What are the pros and cons of LTO tape technology?
>>What are the main differences between LTO 3 and LTO 4?
>>What are the differences between LTO-5 and LTO-4?
>>Will users upgrade to LTO-5?
When Ultrium LTO tape backup technology first came out, the big difference from other types of tape was the LTO Consortium. So, a group of companies came together and agreed on a standard. That allows them to compete in the marketplace without hurting consumers. So you get the good aspects of competition -- tape gets faster, price gets lower, quality gets better -- without having to worry about problems related to interoperability. So, you can buy an LTO tape from any of the vendors associated with the LTO Consortium and it will work with products from any of the other vendors that are a part of the consortium. That's the biggest difference. LTO tape is linear, so the recording head is stationary and the tape moves very quickly across the head. The stripes of data are written in a line from the beginning of the tape to the end.
The biggest benefit is that LTO tape is ubiquitous. It's very common, every company supports it, all the operating systems support it, etc. The price is also a selling point. It's inexpensive and reliable. It outsells every other drive type in the midrange open-systems market by a significant margin. Another benefit for data archiving is the write once, read many (WORM) technology that was introduced in LTO-3. This feature ensures data integrity for long-term data retention.
The disadvantages of LTO tape are similar or the same as other linear tape technologies. Because the tape moves at such a fast rate, there are dozens of feet of this tape passing the head per second. The problem with this is known as shoe shining. Shoe shining happens when you send data to the tape at a rate that is significantly slower than the rate that the tape is expecting.
Tape has to write at a certain rate to get a good signal-to-noise ratio. If a tape is designed to run at 120 MBps, that's the speed it wants to go. When you send something like 20 MBps, it cannot go that slow. So, it speeds up to 120 MBps, writes the data, and then looks to the buffer which is now empty because you aren't supplying the right amount of data. Then, the drive stops and rewinds dozens of feet of tape across the write head.
This back and forth shoe shining motion of the tape across the head wears out the tape while you decrease the throughput of the tape. Your 20 MBps turns into 10 MBps, because the drive isn't writing data when it is shoe shining. However, stepping technology has been introduced, which allows drives to step down in speed to compensate. LTO-3 and LTO-4 tape drives can step down to 25 MBps plus compression.
Speed and capacity are the main differences between each generation. There is more and more data out there, so customers are looking for more and more capacity. The capacity of LTO-3 is 400 GB and it was increased to 800 GB for LTO-4 and there was a similar increase in speed from 80 MBps to 120 MBps. Those were the main differences for any generation of LTO and its predecessor.
However, LTO-4 introduced something very different, with drive-level encryption of backup data. Using a chip that works very much like the compression chip, LTO-4 users can encrypt data inline at line speed.
The main differences are going to be speed and capacity again. There is almost a doubling of capacity from 800 GB in LTO-4 to 1.5 TB native capacity for LTO-5. Interestingly, the data transfer rate only goes from 120 MBps to 140 MBps. Historically tapes have gotten faster as the electronic process for writing to tapes is refined. The tape doesn't get any bigger but more data can be written to the tape because the bits are stored closer to each other. When you store the bits closer together the tape gets faster by default.
It's interesting that the capacity almost doubles with LTO-5 but the speed only increases by 10%. I think that's a good signal from the LTO Consortium that they understand that tape users need bigger and bigger tapes, but that they don't need faster and faster tapes. I applaud them for not doubling the speed from LTO-4. The faster the drive gets, the harder it is to stream data to the drive at the appropriate rate.
It's all about the capacity. It's no secret that the world is more and more interested in disk and less and less interested in tape. However, there is still a huge market for tape for backup as well as for data archiving. Some people haven't been bitten by the data deduplication bug. Some have done the math and found that tape is still cheaper, even after deduplication. We have to deal with encryption, but the tape drives have native encryption now.
There are many people that are not enamored with disk backup or they don't need it, so there is still a significant market for tape for backup and especially archiving. There is no other medium that offers what tape does for archiving. The only real competition is optical, and the significant difference in price is such that most people don't even consider it.
I think that, because users will always want to store more data in the same footprint, you will see users continuing to upgrade their tape infrastructure. Maybe not as many people as there might be if there was no disk backup and data deduplication, but still a significant number.