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It's best to think of the current storage media as a temporary holding area for your data until something better comes along. While less than perfect, today's storage media can maintain your files until something else comes along.
Hard Drives: External USB and Firewire drives offer a simple, low cost, and large area for storage. They can be stored on the shelf and plugged into a computer when needed. However, one slip of the fingers and the drive falls on the floor; resulting in the total loss of data. The importance of redundancy is very critical with hard drives. Even if you never drop a drive, hard drives have been known to crash on their own and loose data.
The bearings of hard drives have been known to freeze up when you place then on the shelf for several years unused. Thus, one should run a yearly disk scan just to make sure that the data is still intact. At the first sign of trouble from any drive, copy the second drive with the backup copy of your data before it fails. The lifespan of a hard drive will vary, but it's reasonable to expect around 3 to 7 years from a drive with normal service and even longer with partial service.
Optical Media: When CR-R disks first came out the promised lifespan was 50 to 100 years. However, some people encountered problems with disk de-lamation these reports caused people to worry that the optical media wouldn't be a good archival media. However this was a case of the cheaper quality disks making the good quality disks look bad. My oldest CD-R was burn in 1997 and is still readable.
Name brand disks, like TDK, Maxell, Verbatim, Panasonic, and Sony are likely to be good quality. Details of how to determine the source of the disk is found at the links below. In general, the deeper the blue/purple color of the disk, the better the quality.
http://www.digitalfaq.com/reviews/dvd-media.htm
http://www.cdr-zone.com/articles/recordable_dvd_quality_page_1.html
When archiving video to disks, always archive the same file to 2 different disk brands. In the event that you accidentally selected a substandard disk, the other disk should survive.
SL (Single Layer) 4.7GB DVDs are relatively inexpensive per GB, however the smaller size of the disk, means a lot of work burning to lots of disks. the DL (Double Layer) 8.5 GB DVDs will require less disks to store your files, but cost considerably more per GB. Both the SL 25GB and DL 50GB Blu-ray recordable disks look promising for the future, but the cost will need to come down for most of us to consider this option.
A life span of 50 to 100 years for optical disks may be possible, but one must protect the disks from excessive light, heat, and cold. Studies show that both direct and indirect sunlight shortens the life of the data on the disks. So store the disks in a dark place.
Flash Memory: As flash memory prices continue to drop, many videographers who use cameras like the Panasonic HMC-150 simply save their original video in the SDHC card it was first recorded on. Even if you don't use SDHC cards, USB Flash Memory sticks can be used for storage.
Unfortunately, very little data exists as to the archival quality of flash media. Assuming good quality flash memory, the storage life may be 10+ years to 40+ years. I just wish I had more information to be able to talk about which flash memory chips will survive that long and which chips won't.
Of interest is the SanDisk WORM (Write Once Read Many) memory. This may prove to be a possible solution for the future. Sandisk reports that the data is expected to survive up to 100 years
Tape Backup: There seems to be a sense of irony for me to suggest that one could go tapeless by backing up to tape. However tape back up systems are a possible means of storing your long term data. Done properly, tape is expected to last about 30 years. Several things are very important to do when using tape.
First, one must have a minimum of 2 working tape drive units. In the event of 10 or 20 years down the road, if one drive fails, you will need the other drive to read your data. It's possible that in 10 to 20 years the standard for tapes may change and you will not be able to purchase a tape drive that can read your old tapes.
Second, when writing to tape ALWAYS verify after a writing. There are several cases of people who ran backup tapes from the server and did not verify after a write. The tape drive went through all the motions, but due to a problem, wrote nothing to the tape.
Third, tape has a limited number of passes it can be written and read from. This is not going to be an issue if you write to a fresh tape and check it every few years.
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