You may have seen the news article on using Blu-Ray for archival data storage. This got me thinking and doing some research on Blu-Ray technology to see if it is really suitable for archiving things for long periods of time. The news article seems to think it’s a good idea, but I disagree, and here’s why:
Interface
The interface for Blu-Ray is either SATA or USB. USB is an extremely poor interface in terms the high data reliability of the channel. The channel was never designed for data high reliability and has a much higher potential for silent data corruption than the SATA channel, which has a much higher potential for silent data corruption than SAS or Fibre Channel.
So if you really care about your data you would be using the SAS or Fibre channel interface. Because Blu-Ray does not support these interfaces, Blu-Ray would be off my list for archival devices
End-To-End
The Blu-Ray standard does not provide any means of doing end-to-end data protection. With SAS devices on disk you have the ANSI T10 PI/DIF standard, which is supported by all disk vendors and I’m pretty sure all HBA vendors, as well as a number of operating systems including Linux, AIX and Solaris for sure. Tape, which is the most used cold storage archival technology, has its own ANSI end-to-end data protection, which ensures that each block is written correctly.
Hard Error Rates
Enterprise disk hard error rate is 1 sector in 10E16 bits. Nearline drives with SAS interface (4TB drives today) have a hard error rate of 1 sector in 10E15 bits. LTO tape is 10E17th bits and enterprise tape is even a few orders of magnitude higher. All of this data is published and well known. What little I could find on Blu-Ray was 10E12, which assumes the data is in 512 byte sectors (which is unclear from the document). This means that every 9 TiB, I get a hard error =10000000000000/(1024*1024*1024*1024).
If the optical industry wants to move toward the archive market they need a lot more reliability, end-to-end data protection and transparent easy-to-find information – no matter what any news article suggests.
