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Backup Is Evil – Part 3 – Using Tape for Archives

April 3, 2010 Leave a comment

Why tape may be unsuitable for long term archiving

Other than the difficulty of expunging data which should no longer be kept, tape is a poor choice for long term archives for two other reasons. The first is that the Commonwealth and State Electronic Transactions Acts for the legal requirements for electronic transactions, and archiving procedures for electronic records state that data retention methods must allow for changes in technology. Tape has a poor track record in meeting this requirement, where for example data recorded on a “DLT III” tape cartridge which was still widely used less then 6 years ago, cannot be read by any commercially available tape drive today

Secondly “For any information kept in electronic form, the method of generating the information must provide a reliable way of maintaining the integrity of the information, unless a specific storage device is provided for by the relevant legislation.” [3]. Tape is a relatively delicate contact media, which degrades with use, can become physically damaged and is adversely affected by swings in environmental conditions. Data stored on tape can also be lost from exposure to magnetic fields. Thus, in order to provide “a reliable way of maintaining the integrity of the information” tapes must be periodically refreshed (read and rewritten). Managing refresh cycles for hundreds of tapes written over many years is a complex and an extremely costly task with potentially serious consequences if not managed properly.

Is tape really capable of keeping data for long periods of time ?

Some tape media such as LTO-4 is often touted as having a 30 year archival life. For a technology that is less than three years old, this kind of claim can only be relied upon through a fair degree of faith in the vendors’ statistical analysis techniques. IT and business management are asked to take this leap of faith while accepting that unlike disk, there is little or no hard data published for tape on “mean time to data loss”, or annual failure rates under various conditions. Given the high rates of dissatisfaction with tape based backup, vendor claims of long-term reliability may need to be reviewed with greater vigor.

Tape is only as good as its handlers

One of the major failings of tape, is not the technology itself, but the way in which it is treated. In many cases the staff entrusted with tape management and movement are in entry level IT positions, or semi skilled third party couriers. Even tape media manufacturers openly acknowledge that expected archival life times are only for tapes kept in “optimum” operating and storage conditions of 16C to 25C ,Relative Humidity 20% to 50%, and no shock or vibration, none of which apply to courier vans. In addition, tape drives must themselves be subject to rigorous preventative maintenance. The reason for this is that atape that is used in a drive that was not well maintained and has accumulated dirt and debris from dirty heads, roller guides and other transport assemblies, may find this debris gets transferred to the tape media. When these dirty tapes are subsequently used in a good drive, they may transfer some or all of those contaminants and degrade a previously clean drive. As the new drive becomes contaminated, a variety of problems can result, including premature head wear, debris accumulation on critical parts of the drive transport, and then damage to the tape. This leads to an even larger media impact as any new tapes that are used in the drive can also be damaged,

A further cautionary note when using a backup application for long-term archive is that the media is recorded in a proprietary logical format readable only by the originating application. Backup vendors have been known to discontinue backwards read compatibility for their own logical tape formats, and a change of backup vendors, or products from the same vendor may make recovery from archived tapes difficult, if not impossible to do. Thus, true long-term archive would also require archiving the entire backup system including the computer, recording hardware and software as well as multiple copies of the media.

While this post is really more about archiving than it is about backup, almost every backup environment I’ve ever come across is still used to store long term archives on tape media.  Most of the time this works reasonably well, but far too often it doesnt. To put this in perspective, if you needed the data on the tape to defend yourself in a legal battle, how would you feel about only having a “pretty good chance” of getting the informtaion you needed ?

Categories: Archive, Backup, Tape
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