10k drives versus 15k drives: rotational speed issues

I suspect it's down to a conservative introduction of the 2.5" technology. 2.5" drives started out as IDE/SATA drive on laptops and have gotten faster and aquired SAS interfaces over time.

We'll probably see 15K 2.5" drive in due course.

I wondered the same but didn't get around to asking. In my mind it likely has to do with one of two things. The ability to fit a motor capable of spinning the drive at 15k rpm in a 2.5" form factor, or some kind of cooling issue with the smaller form factor at the higher rotational rates.

Hopefully someone on here knows the real answer and can tell us if someone is guessing right or if we are all smoking something ;-)

Thanks Allen.

I went to an HP gathering in Nice (France) in 2005 and they told me that all 15k drives are in fact 2.5 inch. Yesterday we opened up a 300GB 15k disk case and we indeed saw that this 15k drive is a 2.5 inch one !

So the disk drive casings are the same, but the actual platters are 2.5 or 3.5 inches, so IMHO it's not whether or not a motor will fit.

I hope somebody can explain to us if this is a typo in the pdf or that we do indeed seem to have been smoking funny things

Actually I was thinking that the 3.5" case might give them the room to manage the motor or cooling even with the smaller platters. Or do you mean there was a 2.5" casing inside the 3.5" case?

In the 3.5 inch drive case were 2.5 inch platters located. I'll try to find a picture. Hang on.

This is what I mean.

Not the pictures I wanted, but they'll show what I mean. The drive on the right obviously has smaller platters and is therefore capable or rotating at 15k. Can anyone confirm this or have a comment ?

I remember reading a lot time ago that the 10K and 15K drives had smaller platters (3" and 2.5" respectively) because the rotational mass of the larger platters caused too much stress on them at the higher RPMs.  Basically the disks would disintegrate or fly apart because the edges pulled out from the center with a higher force than the material could support.   This forced them to use smaller platters to reduce mass as speeds increased and is also the reason that 15K drives were generally available in smaller capacities compared to 10K and slower disks for a long period of time.

Also, the drive on the right hand looks like a 2.5" drive attached to a heat sink the size of a 3.5" driver carrier.

Perhaps they were having a cooling air flow problem with 2.5" drives in 2.5" bays and putting in them in a carrier that fitted a 3.5" bay allowed for more cooling.

Interestingly the picture on the right does show significantly more in the way of cooling fins and capability (or at least it looks like that).

Mr anderson, this is exactly what I am talking about. Now I want to know if this is still the case. Do all faster drives still contain smaller platters ?

And in my particular example: are the 10k drives in a VNX indeed 2.5 inch and the 15k drives 3.5 inch ? IMHO this is exactly NOT what one would think !

Allen, don't look at the cooling fins ! I couldn't find a picture of a case without them. If you have the opportunity to do the following: please do:

Grab a few old drives which are broken and open them up. The 10k drive is probably 3.5 inch and the 15k is 2.5 inch (at least, it's smaller).

So is there an EMC tech guy around who can answer my question if the 10k 2.5 inch / 15k 3.5 inch is a typo or that the 15k drives really hold 3.5 inch platters ?

I know the VNX documentation mentions the 15k 3.5 inch, but I'm pretty sure this is a typo....

Here's am image of a Seagate Cheeta 300GB 15k SAS drive with the lid off.

As you can see while the drive is 3.5" the platters are not. I've no idea if the platters would fit in a 2.5" drive.

I was questioning the paper I mentioned in my first post. Your comment is valuable, but I still have no answer.

I'm not surprised to see slower 10k 2.5" drives and faster 15k 3.5" drives.

The 15k 3.5" drives may well have same size or even smaller platters than the 10k 2.5" other things also affect the total size of the disk drive.

e.g To go faster a more powerful motor is probably required which will generate more heat which will need more cooling which will need more space.

A bigger drive also means bigger bearings can be used so the spindle does not wobble as much.

Personaly, I'd like to see 2.5" SSDs as a VNX5100 DPE with a mix of up to 25 2.5" drives providing FAST cache (on 2.5" SSDs) and a bunch of 10K SAS

would be a great replacement for my CX300!