In August 2006 I wrote an article exposing the fact that, like any device, tape has a life span. As all of you who read this column regularly know, I am a big proponent of tape and archival storage. I believe that given the hard error rate, the very low power usage and low cooling costs, and the lower cost per TB, tape is the best medium for long-term storage.
Like any medium, tape has a life span, and that life span is not just based on the interface becoming old and no longer supported. Some examples of the interface support issue include Fibre Channel 1 Gbit, Fibre Channel 2 Gbit and Fibre Channel 4 Gbit (likely soon), but that is not what I am talking about.
I am talking about the tape's life based the medium itself. Media wears out for a variety of reasons, including things like the stretching of the tape backing. There are many reasons, and the reasons are not the point of the column. The point is: What are the numbers? What are you going to do about it? What is missing from what vendors tell you, and want you to hear and not hear? Media technology wearing out is not limited to just tape media; it is also true of the disk drive. Again, I am not picking on tape! Try taking a consumer SATA drive, run it 7x24 doing head seeks and reading or writing, and do not try to tell me that flash does not have wear issues, either. Vendors address the flash by wear-leveling and adding extra cells. Anything that is electronic or mechanical will wear out. The real question is, what are the characteristics of this wear out, and what can you do to prevent it before the tape goes bad?
First of all, I want to thank the people at Imation for providing this information and updating the chart from 2006. The information Imation provided included many tapes that are no longer in use. I cut the chart down to what I consider modern tapes. What is clear from this chart is that if you read and write tapes very often, they will exceed what Imation says the tape is guaranteed to -- not that it will fail at that point, but when you exceed the expected usage. Note Imation's data is likely similar to other vendors, but no other vendors would provide the information publicly.
|Configuration||Long-Length Durability *||Example of Usage Life|
|Product Name||Uncompressed Capacity (native)||Total Data Tracks Written On Tape||Data Tracks Written Each Pass||Total EOL End-to-End Passes||Number of Passes to Write Full Capacity (native)||Number of Full Capacity Writes/Reads (EOL)||Years of Life Assuming 1 Full Capacity Write per Month **||Years of Life Assuming 1 Full Capacity Write per Week **||Total TB Processed Over Full Life Uncompressed|
|Imation T10000||500 GB||768||32||4800||24||200||17||4||97.66|
|Imation T10000B||1000 GB||1152||32||7200||36||200||17||4||195.31|
|Imation LTO 1||100 GB||384||8||9600||48||200||17||4||19.53|
|Imation LTO 2||200 GB||512||8||16000||64||250||21||5||48.83|
|Imation LTO 3||400 GB||704||16||16000||44||364||30||7||142.05|
|Imation LTO 4||800 GB||896||16||11200||56||200||17||4||156.25|
|Imation LTO 5||1500 GB||1280||16||16000||80||200||17||4||292.97|
* Long-Length Durability test is typically performed at extreme environmental conditions, and is done without the benefit of cleaning between full capacity writes. Short-Length Durability test is a "shoe-shine" type test over 1 to 3 meters of tape.
** Estimates of life are obtained from long-length durability results using a full file pass as a basis.
No compression is used on any calculations. Compression is data dependant and can be between 1.5X and 2X (typically), up to 3X.
Limitations: This chart is only a guideline and may change dramatically based on the user's daily practices for the care and handling of the media, maintaining the proper use/storage environments, drive maintenance and a number of other factors.
These results beg the question: How long would it take to hit the tape wear-out levels if the drive was running at the full data rate for uncompressed for each of these tapes?
|Product Name||Uncompressed Capacity (Native)||Wear Time at Full Rate in Hours||Wear Time at Full Rate in Days|
|Imation T10000||500 GB||237.04||9.88|
|Imation T10000B||1000 GB||474.07||19.75|
|Imation LTO 1||100 GB||406.35||16.93|
|Imation LTO 2||200 GB||406.35||16.93|
|Imation LTO 3||400 GB||517.17||21.55|
|Imation LTO 4||800 GB||379.26||15.80|
|Imation LTO 5||1500 GB||609.52||25.40|
There is no real trend here. The upside of this is the likelihood of seeing improvements. LTO is up and LTO is down, and there are only two data points for T10000, so that does not provide much information. As Imation makes neither T10000C nor tapes for newer IBM tape drives, I do not have that information. You might say that using an LTO-5 drive and media at full rate for 25.4 days is impossible, and I would totally agree with that. I wanted to provide the raw numbers, and everyone could put in the factors that make sense to them. The point is, you cannot write and read a tape forever. Honestly, 25.4 is a fairly long interval, but bear in mind that tape is usually for archival data, not backup data, these days.
What are you going to do about it?
First of all, I have said time and time again that tape drives do not provide information like disk drives provide soft errors and status. Disk drives provide and export an interface call SMART (Self-Monitoring, Analysis, and Reporting Technology), which provides information about soft errors. RAID vendors use it to determine when to down a drive and start rebuilding. Let me repeat: Tape does not have a standard framework to known information that is collected and analyzed. There are vendors that provide third-party products, and some tape library vendors support collection, but it is not a standard.
This, in my opinion, is a big mistake for the tape drive vendors, as you cannot track the media or drive issues without specialize software. I have said this for years, and there has been no movement by the drive vendors to change it. The only thing that can be done to prevent the media wear-out problem and save data is to buy a product that monitors both tape drives and media and indicates when a problem is brewing. Generally, what happens is that the number of soft errors increases before a tape fails. Also, without software that monitors tape drives and media, you cannot determine how many full tape passes have been made. So in another one of my continual rants about preservation of data integrity, if you manage archives and are not monitoring tape drives and media for soft errors, then you are playing with fire. The tape drive or library vendors should be providing this information for free, which they do not.
This leaves you with one choice: Go out and buy a product that monitors your large archival investment.
What is missing from what vendors tell you?
The big thing missing from the information I have is both IBM's TS1130 and 1140 tape media and Oracle T10000C media. Why don't vendors publish these statistics? From what I have seen, media vendors are scared of drive vendors and other media providers. They will not publish data for the most part, given that the information is difficult to explain. Additionally, vendors do not want to be compared to each other, as LTO is a midrange commodity product, and the real issue for most purchases is price -- reliability is a distraction. Drive vendors that also sell media do not want this information to come out, as it is difficult to explain and distracts the attention from the sale. More information in the sale process that is not generally part of the discussion just slows things down in most sales people's opinion. The problem, again, is most tape usage today is for archive, not backup. The old sales model does not work where people have a long-term interest in their data and often a single or a small number of copies of the information as compared to backup.
Therefore, I put forth a challenge to the industry:
- Whether the tape is enterprise or midrange LTO, all tape vendors should allow the publication of the media information. That means tape drive vendors, tape library vendors and the media vendor themselves ought to have all that public and let the customers decide if the data is meaningful and important to their operation.
- Tape drive vendors should get together and publish standardized error specifications, as the disk drive vendors and industry has done
I am not sure that either of these are possibilities as the vendors are not motivated to make these changes. The fastest thing that motivates a vendor is a customer request. If enough of you make these requests, maybe we will see some change, but I am not very hopeful.
Henry Newman is CEO and CTO of Instrumental Inc. and has worked in HPC and large storage environments for 29 years. The outspoken Mr. Newman initially went to school to become a diplomat, but was firmly told during his first year that he might be better suited for a career that didn't require diplomatic skills. Diplomacy's loss was HPC's gain.