In the first two parts of this ongoing series I explored a few of the ways Blu-ray has been implemented into computers. The first installment discussed Blu-ray readers that would allow you to view Blu-ray movies and also (probably) read DVDs and CDs. The ‘combo’ drive also let you record DVDs and CDs, in addition to just reading Blu-ray discs.

In Part Two of this series, I wrote about recordable Blu-ray – the rather remarkable technologies that let you store as much as 50 GIGABYTES of data onto a single disc. I discussed how single layer Blu-ray discs (BD-R) can store as much as 25 GB of data, while their dual layer (BD-RDL) siblings can store up to twice as much data. It’s not clear whether all recorders (or even Blu-ray readers) can read the second layer of a dual layer disc; or whether a recorder that can write to BD-R media can also write to BD-RDL.

There’s another twist to the Blu-ray story – Blu-ray rewritable (RE – Recordable/Erasable). Rewritable media has been around for more than a decade – with CD-RW, DVD-RW, and now Blu-ray RE. RW technologies, in the past, don’t seem to have been particularly successful – except with those who actually needed rewritability.

Read-write, in the past, had difficulties finding market acceptance – or a compelling market need. There are many reasons for this. The price difference from the standard recordable and the RW discs was typically not great – even when this media was just beginning to become available, the price for RW was often less than twice that for the standard recordable media. In order to use RW media, it had to be prepared for writing (formatted), a process that added an extra step to recording a disc, and that took time to accomplish. In order to write over a piece of RW media, the disc had to be erased completely before rewriting. In the days when the difference in cost between a RW disc and a write once disc was often less than a dollar or two, the financial incentive for reusing an RW disc was minimal – and certainly hardly worth the time spent to prepare or erase and rewrite the media. Further, keeping a stack of interim recorded discs that are made during the course of development of a project probably made more sense, if one ever had to backtrack from a final disc to the interim steps saved while a project was being developed.

Today, with Blu-ray RE, the situation may have finally changed somewhat. In these days when BD-R media may cost $2, $3, $4 or more for 25 gigabytes of storage capacity, the time taken to prepare a disc or erase and prepare a disc for rewriting make the process seem more reasonable. Add to that the fact that a good deal of data can be stored on a BD-RW disc, and it seems that there may finally be compelling reasons for BD-RW.

I can imagine one scenario where BD-RE media would immediately make sense – incremental backups. Consider that your business does full backups weekly, and incremental, daily backups. The incremental backup is a backup that records only the changes made to your data during the period after the last backup. Even very large companies may have problems doing enough changes to its data that it needs 25 GB of storage for a day’s incremental. In theory, you may not need to save daily backups after you’ve completed a new, full backup. If you do this once a week, the incremental backups for the previous week should be unnecessary.

For security, you will probably save weekly backups for many weeks (if not longer), in case you have to roll back your systems or data to an earlier time. At some time, however, you may want to reuse the RW media (because the value of the data on the disc is now minimal) – being able to erase and reuse the media may actually make sense.

Rewritable media is now primarily being sold as BD-RE. BD-RE is available in 25GB and 50GB capacities. The 50 GB media is priced more than double the price for the 25GB BD-RE. For applications where a large database or other application would be best stored on a disc larger than 25GB, the 50 GB BD-Res may make sense. For example, if you’re creating a large video that uses more than 25 GB, a 50 GB RE would make sense. Or, if you were distributing data or program updates that are larger than 25GB, it probably makes sense to put it all onto one disc than to split it into two. If you are using the media to distribute interim materials to other users or remote offices – and where the disc should be erased once the data is transferred to another computer, a larger RE disc would make sense. If yours is an environment where you do NOT want data stored on media once it’s been transferred, erasable media makes a great deal of sense.

There’s another ‘little’ wrinkle to the BD-R picture – the mini-disc. Although small, a mini-disc can hold up to 7.5 GB of data. As with mini-CD and mini-DVD, the mini-BD-R discs represent a niche waiting to be filled.

In the next installment, I’ll be looking at a proposed standard that will dwarf today’s capacities