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I found this, but it doesn't really answer my question.

Disks even in the 1-2 TB range are much cheaper than tapes, yet I saw that Google uses tape drives for backup. What is their (disks) primary disadvantage? I can imagine some sort of disk "library" that is just a bunch of sockets you can slide a SATA disk right into.

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Because for certain workloads and in certain environments it makes sense from a cost standpoint. What makes sense for Google probably doesn't make sense for a small/medium sized business. –  Zoredache Oct 17 '12 at 17:35
    
No need to image a library, they exist. high-rely.com/HR3/index.php –  Zoredache Oct 17 '12 at 17:36
    
The social security administration has completely phased out tape based backup storage, however they have multiple data centers that provides fault tolerance of the others. That being said, we utilized Microsoft's DPM solution paired with off-site disk backups, so it can be done on a smaller scale as well. –  Brent Pabst Oct 17 '12 at 17:37
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Where you buy the tapes? I mean, a LTO 5 tape is a lot cheaper than a corresponding hard disc. At least at all the places I do check. –  TomTom Oct 17 '12 at 17:43
    
@TomTom To be honest, I didn't know much (if anything) about tape technology. You're right, after knowing what to look for, tapes are a lot cheaper than the corresponding disks. –  Corey Richardson Oct 17 '12 at 17:46
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closed as not constructive by Shane Madden, Zoredache, Brent Pabst, Dave M, joeqwerty Oct 17 '12 at 20:44

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4 Answers

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Consider this situation: You drop a box with 6 months worth of backups down the stairs. If these are tapes in their cases, you pick the box back up and continue on your way. If they are disks, you just lost 6 months worth of backups and you'll probably be job hunting.

It's common practice for couriers to take tapes offsite daily and then return them later. Where I work, every day a courier comes and picks up the daily tapes and drops off the tapes from 1 month ago. These tapes typically stay in service for 2 years or more. That means at least 24 trips in and out of our building alone in their lifetime, stashed in the back of a truck, stacked on a shelf, etc. Tapes handle the jostling and jolting of these trips much better than disk.

Also, you can commonly get a 4U library that can hold 30 LTO5 tapes. LTO5 tapes can hold 1.5TB on them. That's 40.5TB of raw backup storage in 4U. You'd be hard pressed to do this with disks.

RDX disks do exist, which are basically an attempt to directly replace tape with disk, but they never really caught on and are generally more expensive than comparable tape with less support because of the adoption rate.


I should mention that a lot of times disk-to-disk archival makes a lot of sense for a lot of businesses. Nowadays you see a hybrid situation where you'll go disk-to-disk with dedupe for normal backups and you write the whole dedupe pool off to tape once a week/month/whatever.

The key to doing this and not losing your job in a disaster is to make sure that you have off-site backups available. For some places, that means putting something like an Exagrid at a colo'd location or dumping your backups on a SAN volume and using that SAN's replication technology to replicate your backups offsite. Whatever route you choose, you need to make sure that off-site storage happens. All of the backups in the world won't mean a thing if your building burns down.

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+1 - Tape beats hard disk drives for durability (though I wouldn't go around dropping them, obviously) and for cost when you need to maintain a long archive window. A lot of tapes are cheaper than a lot of hard disk drives for certain values of "a lot". –  Evan Anderson Oct 17 '12 at 17:30
    
I should be added that a tape in the vault doesn't draw any power and doesn't dissipate any heat. And if the environmental conditions are right, tapes last for quite some time - until the end of it's lifetime, when a tape-robot can copy & replace them quite easily. –  Alexander Janssen Oct 17 '12 at 17:47
    
@AlexanderJanssen Very true, but an RDX disk in a vault doesn't draw any power either :). –  MDMarra Oct 17 '12 at 17:47
    
@MDMarra RDX probably suffers from the "not invented here" syndrome ;) –  Alexander Janssen Oct 17 '12 at 17:52
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RDX suffers from the "this is too damned expensive per GB" syndrome! >smile< I'd be all about RDX if the prices for the "cartridges" were reasonable. –  Evan Anderson Nov 15 '12 at 22:52
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The cost of a tape drive (or library), tapes, delivery to/from your facility, and storage offsite is generally lower than having a redundant data center.

As MDMarra mentioned, tapes are more durable/ reliable and are still an industry standard for backups. The LTO standards are continuing to grow the capacity and speed of tapes. LTO6 is close to release and gives a storage capacity of about 2.5TB uncompressed and 160 MB/s write speed.

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Cheap and offline are the biggies, a lot more below.

He makes the point many times that few enterprises should go tape-ONLY, but tape is still a very important part of many DR plans and compliance requirements.

http://nsrd.info/blog/2010/04/14/10-reasons-why-tape-is-still-important-part-1/ http://nsrd.info/blog/2010/04/14/10-reasons-why-tape-is-still-important-part-2/

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Backups on tapes is still the best practice. Tapes can be changed by robots, and you don't need them attached all the time and are also really fast on sequential writes.

Tapes are also much more robust in several ways, for example: you could store a tape more than 50 years.

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Aye, tapes are still best practise. But it might be worth mentioning why. (Well tested to last long. Hard to damage. Etc. etc.) –  Hennes Oct 17 '12 at 17:45
    
@Hennes i have mentioned that ;) –  Thomas Berger Oct 17 '12 at 18:44
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