Storage technology comparison

An important factor when comparing technologies is the applicable application for each technology. From below you can see a hard disk RAID has a low cost per GB but a poor archive life and needs regular backups taken. WORM tape also offers a very low cost per GB but it's access time is very poor for organisations wishing to retrieve information quickly. Based on a 50 year archival life only optical storage offers the long term archive and retrieval times required by organisations.

* Dependant on tape technology

RW = Read/Write, WORM = Write Once Read Many

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 library 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, this 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 cartridge. The omission of a recording-enabled hole from the media cartridge also safeguards against accidental overwrites. Further data integrity is ensured through the use of unique serial codes assigned to the cartridge during the manufacturing process. Whilst WORM tape has a high capacity and low cost per Gbyte it is let down by it's access time which can be from 30 secs 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, this can sustain two drive failures before data loss occurs. Newer RAID systems now offer RAID 6, this can sustain three drive failures before data loss. 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 - Developed by Plasmon to replace MO (Magneto Optical) technology. It holds 15GB per side making 30GB 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 - Blu-ray, also known as Blu-ray Disc (BD) is the name of a next-generation optical disc format. The format was developed to enable recording, rewriting and playback of high-definition video (HD), as well as storing large amounts of data. The format offers more than five times the storage capacity of traditional DVDs and can hold up to 25GB on a single-layer disc and 50GB on a dual-layer disc. For more general information about Blu-ray, please see our What is Blu-ray? section.

According to the Blu-ray Disc specification, 1x speed is defined as 36Mbps. However, as BD-ROM movies will require a 54Mbps data transfer rate the minimum speed we're expecting to see is 2x (72Mbps). Blu-ray also has the potential for much higher speeds, as a result of the larger numerical aperture (NA) adopted by Blu-ray Disc. The large NA value effectively means that Blu-ray will require less recording power and lower disc rotation speed than DVD and HD-DVD to achieve the same data transfer rate. While the media itself limited the recording speed in the past, the only limiting factor for Blu-ray is the capacity of the hardware. If we assume a maximum disc rotation speed of 10,000 RPM, then 12x at the outer diameter should be possible (about 400Mbps). This is why the Blu-ray Disc Association (BDA) already has plans to raise the speed to 8x (288Mbps) or more in the future.

Holographic Discs - Within the next 2 years holographic storage systems will be storing the equivalent of 63 DVD’s on a single holographic disc of 300 Gigabytes capacity or 35 hours of broadcast quality video. With a 50 year archive life and a road map to 1.6TB per disc holographic storage promises to be the content distribution and archive format of the future.

In summary both the Blu-ray and Plasmon UDO technology offer similar benefits, I think the Blu-ray would be the better long term choice as it has the backing of a huge corporation, uses single sided media and incorporates 2 types of error correction.

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