Storage technologies compared
DVD - Holds 4.7GB of data on a single side and 9.4GB using double sided media. The media is un-protected and requires a rotation mechanism to flip the media over. A DVD jukebox is ideal for storing approx 1TB of data, above this the cost becomes expensive compared to other optical technologies. Although the technology is primarily WORM (DVD-R), to create the pits causes a chemical change in the media. Due to the way the disks are written more care must be taken when archiving DVD media. The other DVD technology that is available and is a better technology than DVD-R is DVD-RAM. This technology was developed by Panasonic, the DVD-RAM disc structure is laid out the same as a hard disk with sectors/tracks and error correction, is supplied in a ruggedised caddy or as bare media, and is more suited for archiving data than DVD-R.
WORM TAPE - For years tape has always been used for backing up information and restoring. Now many companies including Sony, Quantum and the LTO consortium have developed WORM tape. They offer a lower-cost way to store sensitive and regulated data and comply with rapidly growing regulations like HIPAA, Sarbanes-Oxley and SEC 17A-4. Data is written to the WORM tape by using a combination of hardware and software embedded in the drive and the tape cartridge. This communication prevents any intentional alterations or over-writes, even if the tape is extracted from its original cartridge and placed into a different non-WORM drive. The omission of a recording-enabled hole from the media cartridge also safeguards against accidental overwrite. Further data integrity is ensured through the use of unique serial codes assigned to the cartridge during the manufacturing process. WORM tape has a high capacity and low cost per Gbyte, but is let down by its access time, which can be from 30 seconds to many minutes to retrieve an individual file. Although WORM tape has a 30 year life, the reality is that unless it is stored in ideal environmental conditions you might find that the tape has degraded due to the way the media is always in contact with the next layer. Many years ago when large reel-reel tapes were stored for long periods many companies found that all they had was "rust on tape".
RAID Arrays - A RAID has long been used for storing and retrieving frequently used information very fast. A typical RAID will have 5 or more disk drives and be configured with a RAID level typically RAID 5 or RAID 6, this can sustain two drive failures before data loss occurs. A RAID system is constantly consuming power even when not being accessed, no matter how reliable a RAID system is "it will break". A RAID array is a mechanical device with constantly moving parts, over time these parts wear out and when they do the RAID system fails, if a RAID array is so reliable why do we back them up? In my experience a RAID should only be used for fast access to information and should not be considered as an archive medium for 5+ years.
UDO-2 - Developed by Plasmon to replace MO (Magneto Optical) technology. Holds 30GB per side making 60GB per disk, as the media is double sided it requires a rotation mechanism to flip the media over. It can read/write data at 8MB/sec, uses Reed Solomon error correction and has 8K logical sector size. The Plasmon UDO (Ultra Density Optical) uses Phase Change technology to write data, a powerful laser heats a substrate to one of two heat points: At one heat level, the substrate turns to a crystalline structure; at another heat level, the crystalline breaks down to a less reflective amorphous state. A less-powerful laser is used to read the data without altering it. The phase-change method should provide for faster write times, higher storage densities, and a higher read/write life cycle (the number of writes that a spot can withstand before it can no longer change its state reliably). The Plasmon UDO media is housed in a ruggedised shock/dust proof caddy.
Blu-ray - Developed by Sony the Blu-ray disc holds 50GB on a single side. It can write data at 9MB/sec and read data at 11MB/sec, uses Reed Solomon and Picket error correction and has 2K logical sector size. The Sony Blu-ray disc uses Phase Change technology to write data, a powerful laser heats a substrate to one of two heat points: At one heat level, the substrate turns to a crystalline structure; at another heat level, the crystalline breaks down to a less reflective amorphous state. A less-powerful laser is used to read the data without altering it. The phase-change method should provide for faster write times, higher storage densities, and a higher read/write life cycle (the number of writes that a spot can withstand before it can no longer change its state reliably).
