That's what I'm waiting for at work. It takes over 4.5 hours to do a tape backup today.
But I'd imagine the price of a writer might be a
tad higher.
What the hell are you using for a tape drive?
High performance tape drives will dramatically outperform a any Blu-Ray burner. Even LTO2 which is several years old routinely writes at > 60 MB/second across a 100 base T network. Direct attached is in the vicinity of 90 MB/second on an Ultra160 channel. These are 9x and 14x Blu-ray speeds respectively.
Additionally, media costs are way cheaper per GB than Blu-ray. Keep in mind, I am backing up about 26TB / month across 4 drives. I do this in about 6 hours for incrementals daily (26 servers) and about 12 hours for full backups on the weekends.
LTO2 tapes are available for about ~$32/each and right on < $30/each in bulk. These are for 200GB native, 400GB compressed. So you'd need 4 double layer Blu-ray discs and add software compression to get there. Unfortunately, software compression isn't nearly as efficient as hardware compression at that rate so you'd be limited in your backup capability.
Blu-ray media is about 1.5x the cost per piece of media and 1/4 the raw storage capacity. That makes it 6x more expensive.
By the time you scale Blu-ray up to the required levels it is not cheaper by any stretch of the imagination than tape backup.
The only advantage it has is in random access. There are applications where this is apropos -- but there is a reason that tape is king in the backup world.
I can buy an LTO2 drive for about $1000. I can buy 1TB of raw capacity media for another $150. Call it $1200.
To get the same throughput, I need 9 Blu-ray burners (at $2000($500x4)) and 4 pieces of media ($180) to equal the speed and capacity of a several years old LTO2 tape drive. LTO3 is at market and it's roughly double the speed and capacity of LTO2. This just furthers the gap between tape and optical.
Yes, I do think about stuff like this on a regular basis, why do you ask?