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View Full Version : Half life of data stored on a magnetic drive



ssssss
07-10-2012, 09:21 AM
I read somewhere that this is about 6 years.
I am not sure what this means, but it sounds worrying.
How long is it before reading a drive starts giving errors?
Thanks

gary67
07-10-2012, 09:32 AM
I nearly lost a CD of pictures that started to become unreadable after 5 Years, your much better off using a portable hard drive for storage

ssssss
07-10-2012, 09:36 AM
I nearly lost a CD of pictures that started to become unreadable after 5 Years, your much better off using a portable hard drive for storage

Hi gary67,
Aren't some brands of CDs and DVDs better than others?
I usually stick to Imation.

Paul.Cov
07-10-2012, 10:28 AM
Imation is garbage.

Practically all optical media in NZ is off the bottom rung of the production ladder.

Taiyo Yuden is reportedly a very reliable brand (dunno if I spelt it right), but you can never be sure if you're buying the genuine product or some cheap asian knock-off of the TY brand... so it's still a gamble. Discs branded Sony may be made by Princo, which is notoriously foul media. Essentially you can't trust anything to do with optical media at all. Not even the stuff you buy from trusted stores.

Totally agree with Gary, that your best bet is an external hard drive.
The trick to a longer service life from it is to keep it out of service as much as possible. ie when you don't need to be using it, disconnect it from power and from the computer, and put it away somewhere safe, away from vibrations, magnets and kids.

I actually keep two drives like this, so if one fails, there's a good chance the other is still good.
If / when you inevitably find a drive has failed your immediate priority becomes getting a replacement drive and completly copying your other drive BEFORE making any further use of it.

nmercer
07-10-2012, 10:57 AM
back it up into the cloud, for instance www.skydrive.com gives you 7GB for free, or 25GB for free if you were one of the early customers

ssssss
07-10-2012, 11:48 AM
Thanks for the advice.
When you say optical discs are poor,
does that mean that commercial DVDs, like BBC video DVDs have a poor life too?

Slankydudl
07-10-2012, 01:42 PM
half life? this isn't a radioactive substance.

ChazTheGeek
07-10-2012, 01:48 PM
Nooo.

icow
07-10-2012, 02:01 PM
half life? this isn't a radioactive substance.

It's the length of time it takes for a substance to decay to exactly half it's original mass/size/whatever you want to call it.

Agent_24
07-10-2012, 02:25 PM
Thanks for the advice.
When you say optical discs are poor,
does that mean that commercial DVDs, like BBC video DVDs have a poor life too?

Commercial DVDs etc are much more reliable than most CD\DVD-R etc but the reflective layer will still rot after a while, faster if there is a manufacturing defect.

But remember, everything breaks, to keep your data safe have multiple copies\backups and be sure to refresh your devices periodically to combat degradation of the physical media.
There is also the issue of silent corruption which has multiple causes, one way to combat this is a filesystem designed to combat this such as ZFS which implements data scrubbing and checksumming.

pctek
07-10-2012, 03:38 PM
http://en.wikipedia.org/wiki/Hard_disk_drive_failure

Since hard drives are mechanical devices, they will all eventually fail. While some may not fail prematurely, many hard drives simply fail because of worn out parts. Many hard-drive manufacturers include a Mean Time Between Failures figure on product packaging or in promotional literature.


Recently, engineers at Google conducted their own real-world tests. (A PDF copy of the study is downloadable at: http://research.google.com/archive/disk_failures.pdf). The Google study identified several factors that contributed to the early death of a hard drive but the report drew no concrete conclusions.

DriveSavers, a data recovery service provider that has been in business for over 20 years, recommends replacement of computer hard drives every 3-5 years.

CD-ROM and DVD writeable media can fail over time due to degradation of the organic dye layer. Studies done by NIST under harsh conditions of light, temperature and humidity demonstrated sharp increases in bit errors after only 100 hours (with the exception of gold/phthalocyanine technology, which is far more durable).

Disks have been demonstrated to crack at 30,000 rpm due to centrifugal force.

Slankydudl
07-10-2012, 03:47 PM
I know that but the term half life doesn't just refer to its size but also the type of decay which is radioactive decay. Hence me wondering why the term half life was used in the title.

Paul.Cov
07-10-2012, 06:50 PM
I wouldn't worry too much about video data on a PRESSED disc like the BBC stuff.

MPG playback algorithms are made to be tolerant of the odd unreliable byte here and there. At worse you'll get a momentary flash of blocky artifact during playback, but nothing that should bring playback to a halt unless there's quite gross levels of failure going on.

But data (backups, zip files, documents etc) are NOT made to be tolerant of a bad byte, so place zero trust in burnt media for data, and low confidence in burnt media for video, and reasonable confidence in pressed media for data, and good confidence in pressed media for video.

Slankydudl
07-10-2012, 08:47 PM
or you could use MPG to playback your media that you put on the disc.

ssssss
09-10-2012, 10:42 AM
Thanks.

I have some blank Sony DVDs that have "archival reliabilty" written on them.

Not true, it seems. Naughty Sony.

dugimodo
09-10-2012, 11:13 AM
Halflife can also apply to the decay of magnetic field strength over time which is appropriate.
I Like Verbatim and Mitsubishi optical media (same disks actually verbatim are rebranded mitsi disks). They have consistently been in the top 3 of tests I've read and are much easier to get than Taiyo Yuden. But my experience with the long term reliabilty of any writeable optical disks has not been great, and DVDs seem to be worse than CDs in this respect. I have burnt CDs from the early days of CD writers that still read fine, but I have DVD's that have failed after a few months (especially princo). I have had a couple of the gold coloured disks and they do seem more reliable.

Anything critical you should keep a backup of and periodically refresh it. I don't personally worry too much because there is nothing on my PC that can't be replaced. The worst thing would be losing my lossless rips of my CD collection which took me a few days to do so I have 2 copies of that on 2 differnet hard drives. But even then I still have the original CDs if it came to that.

Agent_24
09-10-2012, 11:40 AM
But even then I still have the original CDs if it came to that.

Which will rot eventually.

dugimodo
09-10-2012, 01:20 PM
Which will rot eventually.
Well nothing lasts forever. Commercially produced CDs do last very well though, some of mine are 25+ yrs old and showing no signs of degradadtion. I expect the bulk of my CD collection to outlast me. I'm sure I recall when they first appeared the estimated life of an Audio CD if looked after was something like 70 yrs.

I know some batches of CDs suffered from rot but I don't think it's all that common. Of more concern is either the discolouration of the plastic or the eventual oxidation of the alumininium.

Slankydudl
09-10-2012, 01:54 PM
light and heat will also screw up the dye layer of the cd's

inphinity
09-10-2012, 01:55 PM
I know that but the term half life doesn't just refer to its size but also the type of decay which is radioactive decay. Hence me wondering why the term half life was used in the title.

Half life doesn't specifically pertain to radioactive decay, it's just a term to indicate the time it takes for a quantity to halve in value, and is typically only used for values that exhibit exponential decay (in fact, it could only be used for such, in it's truest sense). In this context, one would assume it is referring to how long it would take for the magnetic strength of the disk in question to halve - which would probably be around 5 - 6 years.

Sanco
09-10-2012, 02:07 PM
Aquila Tech sells genuine Taiyo Yuden discs, they offer competitive pricing and good customer service -- I have used them for years and no coasters thus far. Here: http://www.aquilatech.co.nz/:thumbs:

Renmoo
10-10-2012, 10:31 PM
Aquila Tech sells genuine Taiyo Yuden discs, they offer competitive pricing and good customer service -- I have used them for years and no coasters thus far. Here: http://www.aquilatech.co.nz/:thumbs:

Corrected link: http://www.aquilatech.co.nz/

Digby
11-10-2012, 07:11 AM
It's the length of time it takes for a substance to decay to exactly half it's original mass/size/whatever you want to call it.

So that is what is affecting my manhood!

But seriously yes, data on hard drives needs to be refreshed from time time.
Copy it from one drive to another and then back again.

Renmoo
11-10-2012, 08:55 PM
So that is what is affecting my manhood!

But seriously yes, data on hard drives needs to be refreshed from time time.
Copy it from one drive to another and then back again.
......!?

ssssss
20-10-2012, 09:30 AM
Hullo again.

What about the reliability of USB Flash drives?

Are they more or less reliable than magetic drives?

Thanks.

Agent_24
21-10-2012, 11:47 AM
Less reliable and getting worse, in terms of bit-rot.

http://techon.nikkeibp.co.jp/article/HONSHI/20090528/170920/

Chikara
25-10-2012, 06:31 PM
Less reliable and getting worse, in terms of bit-rot.

http://techon.nikkeibp.co.jp/article/HONSHI/20090528/170920/

That article is from more than three years ago. How much of that still holds true now?