Hard Drive Speed

John Summerfield debian at herakles.homelinux.org
Fri Nov 2 00:15:33 UTC 2007


Alan Cox wrote:

>> * high-end HDs, e.g. 10,000+ RPM. These can improve your performance 
>> somewhat, in the range of 10-20% - but it stacks on top of performance 
>> gain of alternate filesystems. This is probably the cheapest upgrade path.
> 
> Also more but smaller disks. 8 40 GB disks have much better seek
> behaviour than a single 320GB disk. They also take up a lot of room and
> power 8(


Have you tested that? It's not clear to me that that should be so. 
Physical characteristics determine the number of platters that can be in 
a drive, and you generally see a manufacturer release several drives of 
different capacity at the same time.

3.5" drives have from one to (I think) five platters.

At any moment, the five-platter version would have five times the amount 
of data on they cylinder the heads are on compared with the one-platter 
model.

Seek times, when seeks are needed, would be the same. For many 
applications, seeks would actually be needed less often.


Comparisons between different models need to take into account the bit 
density (which translates to the amount of data per track, and the 
number of tracks per cylinder), and _all_ comparisons need to be made 
comparing like areas of the recording surface. It used to be the case 
that all tracks were the same size, but that's no longer the case: 
tracks near the outer rim have more data than the short ones near the 
centre.

Unfortunately, the _real_ drive characteristics tend to be hidden; the 
cylinders/tracks/sectors information on the labels is what DOS might 
see. Even as far back as the 80s, some mainframe drives I knew about 
reported physical characteristics to the OS (back then it was MVS/XA) in 
terms of what the OS supported, and not the true characteristics (on 
those drives, OS could not use the full capacity).


-- 

Cheers
John

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