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Shouldn't the 5.25" and larger form factors for hard drives be more common?

MadRat

MadRat

Lifer
A typical 3.5" hard drive (assuming 3" dia. platter) that rotates at 7200rpm has a tangential velocity of 68000 inches/minute. At the same rate, the tangential velocity of a 5.25" hard drive (assuming a 4.75" dia. platter) would require just over 4500rpm. If we assume the 3.5" platter's read/write strip to be 1" wide then it makes approx. 6.28" square available for data. If we assume the 5.25" platter's read/write strip to be 1" wide then it makes approx. 11.8535" square available for data. If we assume the 5.25" platter's read/write strip to be 2." wide then it makes approx. 17.113490625" square available for data.

Check my math:

3.5" platter area w/1" datastrip = (3.14(1.5"^2)) - (3.14(.5"^2)) = 7.065 - 0.785 = 6.28" square
5.25" platter area w/1" datastrip = (3.14(2.3875"^2)) - (3.14(1.3875"^2)) = 17.898490625 - 6.044990625 = 11.8535" square
5.25" platter area w/1.8875" datastrip = (3.14(2.3875"^2)) - (3.14(.5"^2)) = 17.898490625 - 0.785 = 17.113490625" square

I find it extremely difficult to believe that a 3.5" platter is significantly more expensive to manufacture. Single platter drives (7-12mm thick) built on 5.25" form factor should most certainly compete with much wider 3.5" dual-platter drives. The slower rotational speed of the platter should mean a quieter drive with a longer MTBF rate; I assume the wider platter would be inherently more stable due to its lower rotational speed. Perhaps a whole stack of single-platter 5.25" drives could be able to be stacked inside of a regular 5.25" slot. These benefits are to name just a few. The drawback would probably be seek and read/write times, but the increased time should be insignificant to most end-users.

Just seems that hard drive technology should be developing in several physical directions, but conventional wisdom is mostly limited to just shrinking them. The current drives are shrinking at a fantastic rate and its beginning to look like 2.5" will become the norm in laptops. But for desktops and server farms it would make sense to also increase the physical size of the drives. It should NOT require seven to twelve drives just to get the redundant capacity necessary for a terabyte of storage. Only few 9-12" platters (@20 GB per inch square) should more than suffice to run 1 terabytes in a safely striped set. Wouldn't the price per terabyte be less for large capacity platters, too?

10" platter area w/9" datastrip = (3.14(4.5"^2)) - (3.14(.5"^2)) = 63.585 - 0.785 = " square
Now take " sqaure times 20 GB per inch and we get a capacity of 1271.7 GB.

12" platter area w/11" datastrip = (3.14(5"^2)) - (3.14(.5"^2)) = 78.5 - 0.785 = 77.715" square
Now take " sqaure times 20 GB per inch and we get a capacity of 1554.3 GB.

14" platter area w/13" datastrip = (3.14(6.5"^2)) - (3.14(.5"^2)) = 132.665 - 0.785 = 131.88" square
Now take " sqaure times 20 GB per inch and we get a capacity of 2637.6 GB!

16" platter area w/15" datastrip = (3.14(7"^2)) - (3.14(.5"^2)) = 153.86 - 0.785 = 153.075" square
Now take " sqaure times 20 GB per inch and we get a capacity of 3061.5 GB!!

I couldn't even begin to imagine the tangential velocity on a 16" platter. 🙂
 
>The drawback would probably be seek and read/write times, but the increased time should be insignificant to most end-users.

You're right that it doesn't matter to most end users, but that's not where hard drive research is focused. At the very high end, these same sorts of disks get used in high-performance SAN and NAS disk arrays, and that generates an enormous amount of profit for drive makers. By far the most dominating factor in performance in a lot of systems is the seek time -- if you're doing random I/O to a disk, the number of I/O operations per second is basically limited by the seek/setup time for the disk, not how fast you can shovel data onto or off of it. Without some sort of breakthrough in drive technology, larger disks are going to be spun correspondingly more slowly (centrifugal forces increase as a square of the radius, I believe, which becomes the limiting factor -- if you assume a 3.5" drive can be spun at around 15kRPM, a 7" drive might top out at less than 4000!). Also implicit in a larger platter size is a much larger variance in seek time (like a CAV CD-ROM), which spikes the worst-case seek times through the roof. And unless interface speeds can scale to keep up, larger disks mean less parallelism in a mirrored or striped RAID setup (though that's less of an issue). It may also be difficult to manufacture fast and precise drive heads on that scale, or to produce balanced, error-free platters of that size (though I'm not in the drive hardware business, so I don't actually know; I'm just trying to think of reasons nobody's done it yet).

Now, drives like that might be *very* interesting in lower-performance roles, like medium-term backups (longer than you might flush to a NAS array, but shorter than you'd want on magnetic tape). There, crappy seek time is irrelevant, and all that matters is making it as cheap and reliable as possible. Users doing, say, video editing, also might not care about really high performance if they can stuff multiple terabytes of data into a mid-tower case.
 
You would also need stronger bearings for the platters and for the arm, the motor would have to be stronger and no doubt the random seek times would be higher if it has to cover a wider distance (unless again a faster arm is employed)
 
I think the single most limiting factor is seek time.

A

Other then that, you have to take into effect the weird stuff like disk expansion. Metal expands when it heats up and there is no way around that. If a 1.75 inch peice of metal expands .0002 of a inch at it's edge then a 2.6 inch piece will expand a .0003 of a inch. Plus not only with heat the increase in inertia will cause it to expand some, too.

So the density of the platter will suffer, which in term reduces the read/write times.

I'd hate to see how much a 12 inch platter would expand.

You could lower the rpms and get the same edge speed, but that's only for the bits at the edge. Interior parts of the platter will just be as slow as a 3.5 inch disk at that same speed.

You could say that maybe speed doesn't matter, you could just use this for storage.

But we have other technologies that work perfectly well.

For instance tapes. They can't do random access worth a dam, but modern/new ones can handle sustained data rates upwards of 30MB/s and have capacities up to 400GB's.

With more normal 200GB tapes you can just have 6 and you can have over a terabyte worth of storage.

Hell, with high end stuff you get over a terabyte worth of information storage on one tape drive box with sustained data rates of over a 100GB's a hour.

There is one "magnum 20 library" tape box that holds 14.8 terabytes worth of information and can give 432GB/hour
 
Problems I see are:

Servers are set up for standard sized drives, you might have 1 or 2 5.25" bays but then you have to kick out the CDROM, Tapedrive, ..... (a lot of rackmount gear have no 5.25" and use slimline CDROMS)

Quantum Bigfoot stigma

Need to design and fab all new chassis and drive components
 
The Bigger the Platter the more wobble will occur and the heavier the parts will have to be for stability, and the larger the motor is required and the more heat is created. This has been tried and it did not work well.


Data can be stored in a much smaller amount of space on a single platter for what use to take 3 or 5 platters. This being the Case, Smaller may be better. We do not really need even larger and bulkier PC's. A 2.5" drive would be a better standard.

Phillips took a optical blu laser DVD drive down to about 3 CM which could fit in a matchbox. According to them it holds 1 GB of data. I could easily see a desktop computer shrink down to the size of a paperback book.
 
I think there might be a use for physically bigger drives to replace tape backup. Tape backup tapes are starting to offer worse GB/$ than hard drives even if you only consider the cost of the tape. For backup purposes, speed isn't such and issue so physically big drives won't be so problematic.
 
Does anyone remember the "Quantum Bigfoot" series, that's exactly what they were - lower RPM 5_1/4" drives.

Anyway, here's my list of possible reasons that they dont use larger platters

1. Higher Seek (and higher seek variation)
2. Higher Rotational Latancies
3. Need stiffer paltters or they're more likely to wobble or buckle.
4. Higher gyro-forces if drive is moved.
5. Larger variation in STR between outer and inner tracks.
 
Originally posted by: uart
Does anyone remember the "Quantum Bigfoot" series, that's exactly what they were - lower RPM 5_1/4" drives.
Click to expand...
the bigfoot was the last popular 5.25 " drv. i used alot, inspite of others warning me about their unreliability.
i didnt believe the warnings , after all Quantum was such a good brand. unfortunately for me, the warning were right, most of my bigfoots have failed. so my one word answer why theyre not used more: unreliability.

 
There were a couple of stabs at bringing the 5.25" form factor back.

Quantum did those "BigFoot" drives to reduce cost - by lowering the rotational speed without losing linear velocity, and by using a single large platter to save on the headcount.

Seagate in turn resurrected the huge, full height (two of today's bays!) "Elite" series form factor to make the - at the time - largest possible SCSI drives. They also were good in linear streaming of data. These two properties made them perfect for video streaming applications, particularly when in RAID arrays. Seagate had a 47 GByte drive when everyone else was still stuck at 18 or so.

Quantum's approach was successful for a while, so was Seagate's. Both were stampeded over however, simply because the technical advancements in head and platter technology narrowed the advantages over standard 3.5" drives in a very short time.
 
note that the linear velocity that bigfoot enjoyed only existed at the edges of the platter. In any part of the disk that would also be present in a normal HD the speeds were slower. So it only enjoyed the speed at the edges.
 
Originally posted by: drag
note that the linear velocity that bigfoot enjoyed only existed at the edges of the platter. In any part of the disk that would also be present in a normal HD the speeds were slower. So it only enjoyed the speed at the edges.
Click to expand...

I don't think that was the case. A half inch in from the outer edge the Big Foot series would have had a higher tangential velocity, too.

 
drag was assuming the two disks were spinning at the same RPMs. If that is the case, then (in our particular case of 5.25" vs. 3.5"), the area from 3.5" to 5.25" enjoys an increased linear speed, while the interior portion runs at the same speed as the 3.5" disk (and average seek time will be worse, since the physical disc is larger). If the larger disk was spinning slower, the interior part would be even slower than on the smaller disk.

However, I believe one of the limiting factors is that it's easier to spin a smaller disk faster (due to rapidly increasing centripetal forces and a larger moment of inertia on a larger disc), which is likely to make up the difference. You're just not going to see a whole lot of 10kRPM 5.25" disks.
 
The Bigfoots were about making quiet and cheap drives. They were spinning at 3600 rpm or something.

The Seagate Elite drives had about the same rotational speed as the 3.5" SCSI drives of the time. They were specifically about large capacity and good linear throughput. Consequently, they were not cheap at all.
 
no one has mentioned that those 15k drives actually use 2.5" platters. there's a reason for this-- as some others have posted, big problems are encountered when spinning such a large disc so fast. remember the early 52x cd writers?

I think actually desktop drives should start using 2.5" platters. they're more reliable in lots of ways. and who needs 300 friggin' gigabytes??!?! it just promotes software bloat on an extreme level
 
Originally posted by: dpopiz
.....and who needs 300 friggin' gigabytes??!?! it just promotes software bloat on an extreme level
Click to expand...
well a friend of mine has hundreds of dvds saved and i wish i did too
 
Originally posted by: capybara
Originally posted by: dpopiz
.....and who needs 300 friggin' gigabytes??!?! it just promotes software bloat on an extreme level
Click to expand...
well a friend of mine has hundreds of dvds saved and i wish i did too
Click to expand...

Aside from piracy, legitimate video and image editing (especially at HDTV-like resolutions for video, and the really high resolutions that professional artists use) often requires vast amounts of disk space. And games take up lots of disk space, too -- most full game installs nowadays are well over a gigabyte.
 
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