SCSI question: Why discrete drive sizes?

[AndrewR]

Just something that popped into my head the other day. Why do SCSI drives all have the same capacities (4.5GB/9.1GB/18.2GB/36GB)? IDE drives are all over the place in terms of platter and overall size so why do SCSI drives adhere to such rigid size restrictions?

Just curious.

 

[dowxp]

their platters are the same sizes. notice they are all 2x each other. the spindle speed is fast and its hard to increase platter size when the spin so fast. at least thats what i think

 

[Pariah]

I highly doubt there is some technical reason for the sizes. It's just a standard that companies have decided to follow. IDE sizes are all over because there are so many generations. With 2 or 3 generations released a year you get a lot of incremental improvements. SCSI generations are limited to one a year so it is easier to standardize sizes.

 

[dowxp]

doesnt make sense. there is no standardization. each scsi drive is built differently with different components. thats how innovation works. there has to be a technical reason. not just cuz everyone else is doing it.

 

[AndrewR]

My feeling was that it relates to the fact that these drives are typically in arrays and used for corporate set-ups where size prediction is essential.

Don't know, just seems odd to me.

 

[Pariah]

"each scsi drive is built differently with different components."

True, and all those parts are irrelevant except the platter count, size and areal density as far as capacity goes. How they decided on the multiples they use, I don't know, but there is a definite benefit to having standardized sizes that are multiples. If you examine platter density of SCSI drives the largest size in the family is usually 5 or 6 platters even. Cut that capacity in half, you use 3 or 2.5 platters and so forth with no more than one side or a platter unused, unlike IDE drives where you get all sorts of weird unused portions of platters. You can claim there is no standard, and you would be right in the sense there is no written rule, but I'd like to see you find a SCSI drive produced in the last 4 or 5 years that doesn't adhere to this nonexistent standard.

"there has to be a technical reason"

There is, it's the same technical reason IDE drives only come in multiples of 10. Though I couldn't actually tell you what that reason is...

 

[dowxp]

actually, ide drives dont come in multiples of 10. their platter sizes range from 10, 15 to 20gb..

 

[Pariah]

Out of 19 IDE drives on Seagates page, 16 are a multiple of 10, with 3 15GB drives thrown in which are all older generations. WD has 12 IDE drives in 3 lines right now, all multiples of 10. IBM's current 60GXP, 5 drives, all multiples of 10. The first 4 families of drives Maxtor lists contain 18 drives, only 2 not multiples of 10, and both from the oldest family of drives. Final count, 64 drives, only 5 not multiples of 10, and none of those 5 are current generation drives.

"their platter sizes range from 10, 15 to 20gb.."

There is no correlation between platter size and drive size in the IDE market any more. WD's most recent series has 27GB/platter and the family consists of 60GB and 80GB drives, obviously not a multiple. Maxtor's newest 5400RPM line has 30GB/platter with drives sizes of 80GB and 40GB.

 

[dowxp]

so theres a difference now. so are scsi platter sizes the same? probably not.

i concede. =)

they probably just put them in 10's for consumers.

 

[Soccerman]

Seagate (I think) released drives with something like 37 gig platters, but to achieve 100 gigs they reduced the platter size down to 33 gigs (don't know how they did it) and just put 3 on the drive.

There is no correlation between platter size and drive size in the IDE market any more.

both true and false. Platter sizes determine (at least partly) the intervals between the different sizes offered. Some companies disable part of a platter to achieve a certain number of gigs. Others simply reduce the density a bit.

 

[Woodie]

Corporate market is the driver for SCSI (mentioned earlier). Very often used in RAID arrays (3 - 12+ drives).

Because RAID uses the same amount of space on each drive, you want all your drives to be the same exact size, so you don't have any wasted space. Add the fact that the drives are usually purchased from the server vendor, and the vendor likes to do thing in quantity. Limited # of vendors + customer profile pretty consistent = small variety in devices on the market.

When the 4.3gig drives stopped being manufactured, my company bought like a 1000 of them, to have on the shelf for hardware failures: We didn't want to replace a failed 4.3 with a 9.1 gig!

Just my $.02...

--Woodie

 

[AndrewR]

My IDE drive sizes right now: 16.8GB, 20.5GB, and 27.?GB. Not exactly discrete sizes.

 

[erub]

i wonder why nobody has tried to enable the "disabled" portion of the platters on your hard drives...i mean, i wouldn't do it, too risky and i would have no idea what i was doing, but i'm amazed that i've never heard of anybody doing this

 

[Soccerman]

erub, that would likely require a firmware update, but AFAIK, you can't update the firmware of a hard drive.

 

[bozo1]

<< but AFAIK, you can't update the firmware of a hard drive >>



Depends on the drive. All of the SCSI drives used in Compaq servers can be flashed if the need arises and on occasion, it does.

 

[SUOrangeman]

Well, given the costs of SCSI over IDE, it may be more expensive to experiment and implement varying sizes in SCSI. Granted, it shouldn't have anything to do with platter size, but who knows.

Also, remember the HD manufacturer's choice of 1000000B = 1MB and 1000MB = 1GB. No multiples of 2 as the binary world expects them.

-SUO

 

[tasslex]

<< Also, remember the HD manufacturer's choice of 1000000B = 1MB and 1000MB = 1GB. No multiples of 2 as the binary world expects them. >>



I always forget about that, and my question is WHY? I assume that it's so they can market a 30GB drive, but only actually produce a 27.whatever it is on my 75GXP drive, is that the case?

 

[tasslex]

OOPS

 

[SUOrangeman]

That's exactly it, tasslex.

-SUO