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Re: Experience with 18G IDE HD



On Mon, Dec 20, 1999 at 05:06:38PM +0200, Evgeny Stambulchik wrote:
> Mike Londarenko <londernk@hectic.net> wrote:
> 
> >  On Fri, Dec 17, 1999 at 01:51:54AM +0200, Evgeny Stambulchik wrote:
> >  
> >  > As far as performance is considered, it's not RPM that usually matters
> >  (inspite
> >  > of a big hype), but the amount of cache on disk. Until recently (1-2
> >  years), the
> >  > maximum cache on IDE disks was 128KB, while about each SCSI disk had
> >  > 0.5MB.
> >  
> >  This is not exactly the truth ...
> >  [a lot of speculations skipped]
> 
> Please read the whole thread (to the end); you're replying to a message in
> the middle.

This is exactly what I did, this is why I'm replying only to your
message :)

> Let me repeat here again (uff...): the role of cache is NOT only in
> prefetching data; a more import one, especially in the
> multitasking/heavy-load enviroments is BUFFERING of data, allowing OS to
> communicate with inherintly slow devices at high speeds, in bursts,
> hence

I understand what you mean, but again, in the real world and in real
multiuser, multitasking systems only really HUGE cache can help, 512K-2MB
is near the same in terms of overall performance and as I said, since
you frequently have cache misses it means that you have no benefit from  using
caching at all ! And one more important thing - you can't program the
cache controller of drive itself - it decides what to cache and what
not using its own firmware . 
Just for your information, somebody measured the speed of HDD while
working under NT and compiling programs, running Winbecnch and other
benchmark programs in two cases :
1)caching on HDD enabled
2)Caching disabled
The difference was (don't forget it's relatively high-load) about 3% 
Why ? Because almost anytime drive's controller had to read/write data
directly from plate. Of course cache "helps" for OS, because whenever
it "asks" from drive to read something it can immediately switch to
other task and run some process, do something else, etc. But remember
that almost any OS has other tasks to do which need access to hard
drive. But as need to read/write something grows - the benefit from
cache will be smaller than from rotating speed . 
So, the real benefit will be only from faster (mechanically ) drive,
and not from one with bigger cache . Some tests made under NT (if you
wish to count this OS as *real* one :) can be found on
http://ixbt.stack.net in the Storage section (Russian only) . Other
similar tests were published a while ago at storagereview . 
Look for tests of drives with similar parameters except the RPM and
cache and you will see the difference . 

> letting it (OS) do other tasks in periods between the bursts. This is why
> new UARTs (16550A and up) use larger cache (and let you use _115200_ baud
> rate to communicate with a _33600_ modem - and, BTW, think why with DOS/Win
> you can do it sometimes even with a 16450 UART (1k buffer), and never under
> Linux), and this is why new smart bus-mastering NICs use larger buffers. Or
> do you believe your modem can "read ahead" from N^HBezeq, or NIC - from
> Internet? :)

"Lama hainternet sheli lo oved ? " :))))))))))))
(A question asked by someone who called to Netvision's tech support) 

> >  What does make adifference in IDE drives for your opinion ?
> 
> What it has to do with the current thread? Eli said the only difference
> between IDE and SCSI is the manufacturing quality and so the price tag is
> not backed up by any real factor, and I argued that even maintaing a higher
> quality itself (let alone other differences) does involve $$. So what's your
> point?

My point is , that there is a major difference between SCSIS and IDE
drives as well as between cheap IDE drives and good IDE ones :)  And the
difference is fortunately mechanics, the engines (motors) used in
SCSIS and IDEs are not the same . I mean here the motors used to move
heads and the motors rotating plates . This is not simply mechanical
part, this is micromechanical part, one such motor for moving the
heads sometimes can cost up to $30 (including positioning system) . 
Now compare this to the total cost of some hard drives and think by
yourself, why SCSIs are more expensive . Another important thing is
quality of plates themselves . Or , more accurately, the tests they
have passed . For example there is some test which can show you how
long time will pass until the first bad block will be encountered on
the plate (in normal working condition). There is another one which
check how plate likes hot (many drives got covered by bad-block plants
just because they were intensively used in bad thermal conditions)
etc, etc. 

Now to the Eli's speculations . 
 
For some manufacturers all this - same story and really their IDE and
SCSI drives costs the same money for them , but they can't just broke
the competition by lowering prices - since it will return to them as
boomerang, because at some stage they will want to improve their
manufacturing facilities and will be unable to do that due to the low
profit they make - sorry, no money for that . For example one of the
worlds largest    suppliers of plates for hard drives manufacturers ,
HMT, has very simple policy - everything newer and better in terms of
technology  has to be priced more
than something old even if this new thing costs us less . This is the
way they can get money for other researches and facilities .
But since we're looking at this from the point of HDD manufacturers it
means that they have to decide - what is better for them , using the
old plates which are cheaper but has smaller caapacity or follow the
competition and start using new ones to increase total drive's size ? 
And if they choose the secodn option it means that you get bigger  (in
terms of capacity) drive which is supposed to be much  more expensive
than its older counterparts. Almost the same situation exists with IDE
vs. SCSI drives, hard drive manufacturers choose better parts to
ensure BEST (and not just good) quality and this gives them chance to
provide 5-years or somtimes even 7-years warranty . This is simply
different slice of market, imagine yourself some home user who will
buy the drive today to use it for 7 years ! It's simply impossible due
to fact that on some stage he will be unhappy with its speed, that it
has too small capacity to store user's loved Gabriel Knights XXX (X GB
in size :) and its not modern :) Businesses and serious users need
drives of such reliability and they are ready to pay more for such
goods.

I think that my point is clear now, but to conclude -
SCSI and IDE drives priced differently because :
1)Engines (motors) used are not the same - SCSI uses more precise and
reliable ones
2)Plates too, frequently , are not same and SCSIs are using more good
ones than IDEs.
3)For some of manufacturers (the least part of them) SCSI drives are
just the way to make more money .

> I wonder if anyone maintains a "black list" of Israeli companies
> specializing in hardware. Though, I'm afraid, it would soon become an
> identical copy of the official Company Register (or whatever it's called)
> :^)

Unfortunately seems that you're right ....


> PS. Slightly off-topic: 73.4GB, 10000RPM, 40 MB/s _sustained_, 8MB cache,
> Ultra160 (of course, SCSI :)), to appear in 2000 Q2, $1300 retail. Not
> bad...
> 
> http://www.quantum.com/quantum/pc/pr/pr99121501.htm

Oh, yea, new plates ...



Mike.


-- 
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Computers are like air conditioners.  Both stop working if you open windows.

        -- Adam Heath
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