Take the 2-minute tour ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.

IBM still develop and sell tape drives today. The capacity of them seems to be on a par with today's hard drives, but the search time and transfer rate are both significantly lower than that of hard drives.

So when is tape drives preferable to hard drives (or SSDs) today?

share|improve this question
2  
tape is just a length of plastic with magnetic properties, and that is all you need to transfer data -> no redundant components to ship around –  ratchet freak Nov 5 '13 at 10:48
    
In my opinion tape is only useful for small data requirements. I can't imagine how slow it would be to back up 100TB+. –  Matt Nov 11 '13 at 3:40

8 Answers 8

up vote 43 down vote accepted

For me, the single biggest argument in favour of tape is that doubling your storage capacity is cheap. That is, to go from 1TB of HDD storage to 2TB is the same as going from nothing to that first TB. With tape, you pay a large premium for the drive, but storage after that is comparitively cheap. You don't have to have lengthy budget meetings about increasing the size of the storage NAS by 15TB, you just order another box of LTO5s.

(Chopper makes a valid point about compulsory labels, but tape labels are in a standard format, and there are free software solutions to printing your own onto label stock.)

Tapes are much easier to ship, and easier to store, than HDD and HDD-like media. They're more resistant to shocks, and their temperature tolerances are higher.

They also benefit from the existence of autoloaders. This allows you to spread a large dump over multiple storage containers, which means you don't have to worry about how to break up your backups. While it's perfectly possible to make an autoloader for HDD-type media, I've never seen one, and I suspect the lack of standardisation in physical package size will make it difficult to bring one to market at a reasonable price.

Your point about transfer rates is valid, but in the context of backups it's of minimal import. The time required to back up a 1TB file system to anything is large enough that you shouldn't be doing it on a live file system; and if you're dumping a snapshot to tape, who cares if it takes an extra hour or two? Search times are an equally minor concern, because all decent backup software maintains indices, so one can generally go straight to the relevant portion of the tape to restore a file.

share|improve this answer
10  
The reason you don't need an autoloader for HDD media is because it's entirely possible to "load" all of them at the same time. To get data from a disk, it just needs power and a data connection, which requires not a lot more than a few wires. That scales easily. To get data of a tape, you need an entire drive, and it's not feasible to have an entire drive per tape. –  MSalters Nov 5 '13 at 10:34
2  
I freely concede that it's perfectly possible to have all your HDDs hooked up all the time, but that doesn't fit very well with offsiting your backups. If you're dealing with devices that come and go, as offsites require, autoloaders have a definite advantage. –  MadHatter Nov 5 '13 at 12:08
2  
I agree with all those points, but at that level of sophistication, disc isn't cheap any more. Try pricing a 50TB NetApp with snapmirroring capability, and a 10Gb fibre over 150km, and you'll see what I mean. I don't mean to suggest that tape is the solution to everyone's problems, because it's definitely not - but it does still have a useful part to play in the modern data centre. –  MadHatter Nov 5 '13 at 12:17
14  
I've heard it said that "nothing beats the bandwidth of a station wagon full of tapes driving down the highway." –  Roy Tinker Nov 5 '13 at 18:32
3  
@RoyTinker I think you're referring to Andrew Tanenbaum's quote "Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway." from Computer Networks (1989). –  kba Nov 10 '13 at 1:53

Data retention - if you put a disk and a tape with the same data on it in the same physical location it should last a lot longer on tape than on disk - potentially by an order of magnitude.

Also tapes are generally better at dealing with the rigors of being shipped from primary to secondary/off-site data centers multiple times.

share|improve this answer
    
are tapes less expensive also? –  Howard Nov 5 '13 at 9:59
1  
Not always, for some reason a lot of tape libraries insist on needlessly-expensive tape labels to be put on every tape and that can really bump up the cost. –  Chopper3 Nov 5 '13 at 10:00
    
I've heard the should last a lot longer on tape than on disk thing, too, would you happen to have a source for that? I also recall hearing that SSDs have an even better lifespan (just obviously not density -- yet). –  SpellingD Nov 6 '13 at 15:57

Tapes don't compare with disk quite like that. Tapes are for backing up, and they compare more with deduplicated and replicated disk like Data Domain, or optical media.

The main reason for tape backups is that it's cheap. You can afford to store 10 full copies, even though you don't really need them, because the media is so affordable. The next main reason is that it's easy to offsite the data. Hard drives don't travel (or jostle) well. Tapes do, for the most part, and can be brought offsite. Offsite full backups can also be accomplished with things like replication, but that's a lot of money to your ISP.

Really, boiling it all down, it comes down to cost. Tapes are cheaper than their competitors or it wouldn't exist.

share|improve this answer
    
+1 for off siting data. There are still loads of commercial and industrial centers where the most upstream bandwidth you can buy is 1 Mbps per physical line. It doesn't take much churn to swamp that. –  alx9r Nov 6 '13 at 18:55

In addition to all the above, there is generally "less stuff to fail" with a tape. It's a very simple device, and you don't have to worry about the onboard electronics (the drive controller with a disk, even SSD). Additionally, their storage and transport requirements are generally a bit looser. They can be subjected to heat and humidity swings as well as acel/decel forces that normal hard drives just cannot.

Lastly, there are sites that have enormous infrastructures built around tape storage, with many tens of thousands of dollars sunk into tape silos. We can assume these devices will continue to operate for a while, but drive interfaces change yearly. A DDS3 or DLT tape I wrote in 2001 I can still find a drive for; this is not quite the same story for old U320 SCSI.

share|improve this answer
    
"Tape Silo" good way to descript a massive array of tapes I remember seeing in an image of a Google facility. –  tombull89 Nov 5 '13 at 14:29
    
And you can keep the investment in the autolader/silo by just upgrading the drives and tapes within it –  mfinni Nov 5 '13 at 16:51
    
Uh, @tombull89, "tape silo" is in fact the term for an automated array of tapes. I've worked around such things for years. An example: luxmentis.com/blog/wp-content/uploads/2011/10/IMG_4277.jpg –  Jane Avriette Nov 7 '13 at 13:28
    
@JaneAvriette apologies, the only tape machines I've dealt with is a 24-slot HP one. I didn't know there were larger versions. –  tombull89 Nov 7 '13 at 13:56
    
Actually some tapes also contain electronics. All LTO cartridges are equipped with a chip. Sometimes that chip breaks. But usually you can still read the tape if the chip broke, but you cannot write to the tape anymore. –  kasperd yesterday

as everyone has mentioned Tape Drives are used for storage and normally secondary back-ups in large domains.

We would use hard drives as primary backups and tapes as our secondary offsite storage methods. Some companies will also use tape drives for data that is accessed very infrequently.

Tapes currently give about 8.5TB of storage with 353MB/s transfer rates, perfect for large data storage that does not need to be available 24/7

They have already achieved storage density of 29.5 billion bits per square inch with magnetic tape media about 35TB (http://www.zurich.ibm.com/news/10/storage.html)

share|improve this answer
1  
Also check this article: newscientist.com/article/… –  AquaAlex Nov 5 '13 at 14:17

One additional reason for tapes, not stated in the other answers, may sound lame, but nevertheless worth considering.

Hard drives are familiar objects. One may be compelled to steal hard drives to browse through internal corporate data for personal purposes or for selling them off. The reason may even be to augment the home storage for what it takes (an IT department of a large organization will frequently have spare SAS adapters lying around to make this option rather attractive).

However, tapes are much less compelling as "stealables". Many people, including younger IT guys, won't even recognize them as data storage devices. The drive is heavy and requires special software to operate. Even without dedicated encryption, the on-tape data format will not be immediately recognizable by the casual attacker.

In situations which call for large amount of back-up material to be kept on site (to quickly recover from system errors, rather than protect the data from catastrophic disappearance) this may become one of the more important factors to consider.

share|improve this answer
2  
"security through ignorance", just a step away from security through obscurity! –  Javier Nov 6 '13 at 17:33
1  
There's a great divide between Platonistic world of ideals and a real world we live in. –  oakad Nov 7 '13 at 0:28

Question: "search time and transfer rate are both significantly lower than that of hard drives."

  • Sequential read is good enough in certain scenarios.,
    Like movies, music, other audio playbacks. Taps are great for this.

  • Tapes does not requires highly complex enclosures like hard disks, SSD.

    But HDD/SSD almost replaced Tapes by density & speed, ect.,

share|improve this answer
    
This does not seem to directly answer the question. The OP was not about Audio or other similar media. Tape drives and enclosures can be complex with multiple drives and robots to move tapes. –  Dave M Nov 6 '13 at 19:53
    
Totally agreed! Anyone who doesn't think tape enclosures aren't complex has never seen something like the quantum.com/products/tapelibraries/scalari6000/index.aspx - 96 drives, 12,000 tapes. I've been at colos where the tape library had a front door, so you could walk inside (if the robots were off). –  MadHatter Nov 13 '13 at 8:10

Mostly for backup/archival purposes.

You can't get the same storage density for the price with HDDs

Also, as mentioned above the autoloading/form factor aspect is important, you can load up a tape library magazine with tapes and let enormous backups run on them, pulling out tapes as they get full. With the exception of a SAN you generally just don't physically have enough storage ports on a server to do the same thing efficiently, nor an appropriate standard operating protocol to turn off and hotswap drives, it would be an ad-hoc thing.

Finally in terms of organization and inventory, we order the tapes with our labels already printed on them. You scan the barcodes, note where the tape is and you're done with it. I don't know of any similar solution for hard drives except if you were to scan the serial number barcodes, which are much smaller and more prone to be rubbed off.

All that being said MAKE SURE YOU USE GOOD BACKUP SOFTWARE with your tape library. The way the metadata about backup sets is kept and especially the RECOVERY aspect of the software is VERY important when you need it. EMC Networker is the only one I've used thus far and the recovery function is pretty awful.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.