Can anyone knowledgeable explain why they use Blu-Ray instead of tape backup? When would an organization use Blu-Ray, and when wouldn't then? Is this reflective of any kind of general trend?
1) As blu-ray is a consumer product its probably manufactured in greater quantities than backup grade tapes, and therefore can be had lower in price, and there are more vendors to source them from. Similarly the drives themselves are cheaper.
2) Tapes aren't random access, therefore it's slow and cumbersome to retrieve single files.
Re: 1) Looking at the prices on Newegg, 1.5TB(native) LTO5 tapes run about $30.00, so $20 per TB. Write-once BluRay looks to be about $32/TB, and rewriteable is $80/TB.
Re: 2) Although it would take an hour or so to search through an entire tape if all the files were written in a single session, normally backup software writes files in sessions containing a few GB. You can seek to a specific session in about 30 seconds average. So if you put about 4GB per session, it would take a max of approx. 30 seconds to read in that session to retrieve a file. So figure about a minute to retrieve any file. Also, LTO5 transfers about 140MB/sec, vs. 6x BDR disks (what I'm seeing for cheap right now) is only 27MB/sec.
3) IIRC most tape storage technolgies are closed source. FB has been heavily pushing their open compute project. Using BDs get them past a lot of licensing problems.
and LTO has way less licensing problems than Blu-ray and LTO-6 has a max of 2.5TB. LTO is also guaranteed to to read tapes from 2 generations earlier and write one generation earlier. Blu-ray has no such long term guarantee.
Not knowledgeable either, but one difference is durability. LTO is rated 15-30 years while the video notes the blu-ray discs FB uses are "certified for 50 years of operation" and some go up to 1,000(!).
Any media is as durable as the availability of media reader. I seriously doubt, in 15-20 or 50 years, you will have the media reader available to read either of the media, whether tape or BD.
How many 8" or 5.25" floppy disk drives are around today and usable with current server hardware? Anyone who is considering cold storage on media for more than 10 years lifespan is fooling themselves.
A few years ago I had a customer who had to perform data migration from DLT to LTO-3. That was over 24 month project and customer begging the vendor to provide a few old DLT drives to read. On top of that the provided DLT drives were so finicky communicating with modern server hardware that they barely kept up for a few hours before going offline.
> I seriously doubt, in 15-20 or 50 years, you will have the media reader available to read either of the media, whether tape or BD.
Today's Blu-Ray drives are perfectly capable of playing an audio CD from the 1980s, and compatible players probably will continue to be available for another 10-20 years even after everyone stops buying content on physical media.
I wouldn't be surprised if I can plug in my USB 3.0 CD/DVD/Blu-Ray combo drive into a USB 7.5 port in 2030 and use it to play an audio CD from 1980, provided that the disc is in good condition. That's a lifespan of 50 years!
Even in the digital age, well-designed and highly forwards-compatible forms of physical media can last a long time.
15 years isn't that long of a time. I have CDs from much earlier than 1999 for sure, and the media reader is sitting right in my living room. And I'm not even running a data center.
The cost of cartridges are comparable to optical disks. However, LTO drives are non-trivial in terms of both mechanical complexity and cost. I can toss an optical tray into the recycle bin without batting an eye. Not true with LTO, and I suspect their MTBF is similar (trade the quality of the LTO drive for the mass production and cheapness of the optical tray).
Enemy #1 in a large data center is power. When he mentioned the entire rack pulls 1,000W for the density suspected in this thread (~500TB to ~1PB), that piqued my interest. Even if you can't push 2-3PB per rack, the top stat you're crunching forever and always is watt-per-gigabyte. Space is important but if it breaks into the top spot you've done something else wrong along the way.
Enemy #27 for cold(ish) storage might be, say, pressure per sq. in. on your floor. I'd be interested to see a weight comparison of a fully-loaded LTO/cartridge rack and this design.
Perhaps not what you were looking for in an answer, but I'm interested to look over the schematics.
