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September 2016
Data Storage

Saving your stuff!

The computer world is constantly changing. New technologies come and go so quickly it seems that dairy products have a longer shelf life. So how can you store important data for the long term? By that I mean hundreds or thousands of years, maybe longer.

Long Term Data Storage
Two fundamental questions;
  1. How long will the storage media last?
  2. How long the storage media will be in use?

What choices do we have?

Removable media;

  1. Magnetic media, (floppy disks and tape) these would not be a good choice, (see why).
  2. Optical media, (CDís, DVDís and Blu-Ray) this is a better choice than magnetic media but still problematic, (see why).
  3. Flash memory, (USB sticks, Flash cards and Solid State Drives) like the optical media it gets us past the first fundamental question. The second fundamental question is not such a sure thing, (see why).

Fixed media;

  1. The most common are hard drives with the magnetic coated spinning disks. These disks frequently suffer from mechanical failure. Even the modern ones have a life expectancy on maybe ten years
  2. Solid State drives which are basically flash memory devices. These do not suffer from mechanical failure like their magnetic cousins but they are not infallible either, (for the same reason as flash drives).
Cloud Storage; This is the best choice for long term storage currently available. The ďcloud storageĒ is at some data center with redundant power supplies and communication links. Backups of the data are a constant, ongoing and monitored process. The computers are kept in a climate controlled environment where multiple computers are linked together to act as one so that if a failure occurs then the other computers take over until a human replaces the failed unit.

The computers access data on a drive array which consists of several hard drives arrayed together to act as one. Much like with the computers if one hard drive fails then the others take over until a human comes to repair the array. On top of that several data centers exist in different regions such as Denver, New York, London and other sites around the globe. They are linked together by redundant communications lines so that if one data center suffers some calamity like a flood or earthquake the other data centers remain on line.

When new technology overtakes the current state-of-the-art equipment at the data centers humans phase it in while keeping the data from the old system and then migrating it to the new equipment. This way we can get past the first fundamental question of storage media longevity and the second question of hardware lifespan. The data is always duplicated and never in just one place.

The down side of this is that once you put something on the cloud it never really goes away. Be careful with sensitive information because it is always possible that someone else could gain access to it in the future as some celebrities have found out, much to their chagrin.

Magnetic media;
We had the 5ľ inch floppy disks then we had the 3Ĺ inch floppy disks. In both cases the media will only last a few years. The magnetic coating begins to flake off the Mylar disk taking the data with it. Within a decade or so the media is unreadable even with ďproperĒ care. Not to mention the small amount of data that they actually held, just 1.2 and 1.44 MB respectively.

And those two formats are not available today. In just a few years time, (remember we are talking about long term here) the industry has changed. You canít buy floppy disks in a store anymore and even if you had one can you find a computer that has a floppy disk drive in it?

Magnetic tape is even more outdated than floppy drives. Even back when it was the only choice it was a poor choice. Just finding the data somewhere along that long strip of tape made them very slow. And the magnetic material would flake off and accumulate on the tape heads, of course taking the data with it. Backup tapes often had to be replaced two or three times a year. Suffice it to say, I have never been a fan of tape systems.

Punch cards;
OK I am going way back now. In the computer world that ended thirty years ago, although some election officials didnít seem to get the message until much later. The little holes punched in the cardboard were supposed to represent data bits but just get one card in the stack out of order and the system fails. Slow and error prone data storage meant that computers were just not reliable devices back in those days.

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Optical media;
CDís, DVDís and Blu-Ray disks are much more durable that floppy disks. Eventually the polycarbonate plastic will degrade and become milky white rendering the disk unreadable. But if you keep them out of sunlight they may last for millennia. That helps with the first basic question of how long will the media last. The second question is more problematic. CDís have largely been replaced by DVDís and Blu-Ray is beginning to replace DVDís. A thousand years from now the CD itself may still be good but will there be any CD players around?

Another feature of optical disks is that once the data is recorded it is permanently burned to the disk. Once the laser burns the little dots or dashes into the media there is no way to un-burn them. Even the rewriteable disks still have the original data encoded. They just keep moving to the unused part of the disk. Eventually the disk fills up anyway. The exception to this is the phase change storage used in some of the new rewritable Blu-Ray disks. Those can be erased and rewritten.

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Flash memory
Flash memory was developed by Toshiba back in the early nineteen eighties. There are two basic types, NAND and NOR named for the type of logic gates they are based on.

The NOR type is more commonly used in Computer BIOS, Set-top boxes and automotive computers where the program seldom changes. It has long write/erase times but allows random access to any memory location but the endurance may be as little as 100 erase cycles.

NAND type is more commonly used in USB, flash drive and solid state drive devices. It is faster and requires less chip area per cell. But it does not allow random access, data must be read on a block-wise basis and the block size may be thousands of bits. NAND type also has much greater endurance with over a million erase cycles.

And remember Ė Always Back It Up!

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