I want to buy a hardisk now but I don't like hardisks with lot of plates,I don't feel it safe
which are the biggest ones ? 320gb or 500 gb ?
can any1 recommend me a good one ?

wrong focus. Your feeling on safety does not relate at all to the drives or the manufacturing process. The very best drive you can buy could be taken out by a power surge, a dog knocking over your computer or a dropped laptop, cryptolocker.. etc etc.. just look around on the variety of issues that affect hard disks that are not related to how "good" it is. That strategy of finding the best drive also extends now to also having to find the best power supply, the best controller, the best environment.. etc, and, if your luck is anything like mine, you might just get a bad drive of the batch that is supposed to be the best. IMHO, the "best" is a human opinion, which drives care nothing about.

better to focus on a backup strategy where a drive dying does not mean you lose everything. I kind of see where you are coming from, but also look at it this way: a drive with 1 platter of 500g means the heads need to work double the amount of a 500gb 2 platter drive.

I would say get something like a 1TB Hitachi and create a sound backup process instead of limiting your capacity and still be at risk.

I hope you see where I am coming from.

On a tangent:

Why have I NEVER seen this question posted here:

"Hi, I want to create a good backup strategy. This..xxx is my environment, and this.. xxx are my resources and budget. Can anyone advise me?"

weird.

i think, because this question is asked at computer technicians/sales forum

You are probably right Jermy, but seeing as this advice is given many, many times, not many seem to get the message.

Back blaze just updated their hard drive failure stats for Q3 2015, it might give you a basic idea of how long you can expect some drives to last.
It seems like Seagate isn't doing to well but no surprise there.

https://www.backblaze.com/blog/hard-dri ... y-q3-2015/

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Web: https://www.day1data.de

On the contrary, it appears that Seagate's current models have turned the corner. It appears that WD is now the least reliable manufacturer, at least as far as its Red and Green models go.

https://www.backblaze.com/blog/wp-conte ... 042365.jpg

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A backup a day keeps DR away.

AFAICT the largest single-platter drive would have a capacity of 1TB.

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A backup a day keeps DR away.

I get what from where you coming but I'm sure 1 plate only drives are better,faster and quieter and much more durable, this is pure logic and my experience
I don't have a dog,I don't have a laptop ,only a gamer desktop and nobody is crashing against it
fact is I don't need larger storage than 500gb in 2 disks
now I'm using a samsung hdd252hj + samsung hd322hj, winxp+win7 64, yet I never had a ssd
my backup strategy is : dvds

btw, you not replied my answer,thanks anyways for your advice

can you specify which 1tb hardisk have only 1 plate?

Just about all 3.5" HDDs made in the past 5 years. Just look up their product manuals.

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A backup a day keeps DR away.

Frank ,
Thats Correct .I Love The Seagate 1TB Slim Desktop Drive .Its 1 Platter And Really Whips WDC ass in Speed .The Green is Not even Close To it In Speed .Even When i Erase The Media Completely After a DR Case Is Finished My Software has to wait for WDC to complete job even if both of them are same capacity .Plus The Greens Can Have 3 To 4 Platters And God Knows Which Head is Installed And What Not What a Nightmare To Get Donors Lol

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Regards
Amarbir S Dhillon , Chandigarh Data Recovery Labs [India]
Logical,Semi Physical And Physical Data Recovery
Website-> http://www.chandigarhdatarecovery.com