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Old 07-07-08, 07:56 PM Thread Starter   #1
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Large hard drives...

With the announcement of a 5TB drive by 2010, it got me thinking. Why hasn't there been any 5.25" hard drive lately? Recentyly I found an ancient 1GB Micropolis hard drive that was 5.25" full height and had 6 platters.

Going with upcoming 5TB 3.5" drive, a single 5" platter might be able to do 10TB so a 5.25" half height could do around 30 and full height 60TB.

Aside from large space requirement, why not issue large hard drives? A single drive would cost less than putting a few smaller drives together since you'd need 1 controller board and not as much metal total.

In the meanwhile I got to see if I can find my monster 50 pounds 1/5 feet by 2 feet by 3 feet hard drive and figure out theoretical TB size with modern 1TB per in^2 technology.

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Old 07-07-08, 09:01 PM   #2
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Well, not being a mechanical engineer, I can only guess. However, I do have a friend who is a mechanical engineer who worked on desktop hard drives for IBM back in the early 80's. I don't expect to see him any time soon but if I do, I will try to remember to ask him for an opinion.

That much being said, it would do well to remember that the overall trend is towards smaller platters and there has to be a reason for that.

My guess is based on the fact that the circumference of a circle is exactly pi*diameter. So in order to maintain a uniform sector density, a hard drive must decrease in speed as it moves from the inner edge of the platter outward. So using a few huge platters would require more capable motors and electronic that using more and smaller platters.

However, the nit that I would have with that guess is that if I am right, then the whole Matrix RAID thing needs to be called into question.
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Old 07-08-08, 02:30 AM   #3

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I would have thought its an RPM issue too, although slightly different
The outer edges of a 5 12 platter are going to have some serious force acting on them at 7200RPM

If my numbers are right, they may not be, the outer edge of the platter would be moving 2.7km a minute.
A 2.75" platter would do less than 1.5km a minute.

It goes way past my understanding of mechanics to figure out what that means, but I think its a big number for something that delicate.
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Old 07-08-08, 03:02 AM   #4
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The bits would fly off the platters!

Um nah it's probably just a trend toward massive storage being in farms of rack servers with space constraints. Although you'd think a massive 5.25" drive in a 2u or whatever rack could be beneficial. Otherwise who knows, if it's not a technical consideration then it may be a manufacturing one, I'm thinking economies of scale plays a role here.

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Old 07-08-08, 04:31 AM   #5

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Access times. It takes longer for a random seek across a larger platter.
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Old 07-10-08, 01:40 AM   #6

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There are several reasons.
1) Cost - Materials cost more to create a 5.25" drive vs smaller, especially when trying to yield large media at current bit densities.
2) Demand, no one is demanding a larger form factor and capacity is increasing fast enough for the average user (sorry, power users don't represent a big enough market).
3) Power consumption, it takes much more power to spin bigger disks.
4) Heat - imagine how much heat a 5.25" disk spinning at 7200 RPM would generate.
5) Performance - Right now drives use Zone Bit Recording that break the drive up into zones. Unlike CD or DVD the drive does not have to have a constant data rate so the RPM is maintained constand but the bit density is changed depending on where on the surface the data is at. This allows more bits at the outer diameter and fewer bits at the inner diameter. Now imagine a 5.25" disk, the inner diameter would have much fewer bits than the outer so transfer rates across the drive would be degrade quite a bit.
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Old 07-10-08, 05:10 AM Thread Starter   #7
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it would have been nice to see a 5.25" half height drive that can push 10TB.

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Old 07-10-08, 05:33 AM   #8
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also, you can jam as many platters in as you want, but it is going to slow the drive down due to the fact that the seek arms (sorry, not sure if it is the technical term) all move together. more platters = more chance of thrashing when trying to access small files scattered about the drive.

but with large files, it wouldn't really be a problem as they tend to stay in consecutive order.

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