Mike Londarenko <[EMAIL PROTECTED]> wrote:
> > 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 !
I'M TALKING ABOUT BUFFERING, NOT CACHING!!!!!!!!!!!!!!!!!!!!!!
> 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 :)
Not quite. But a more important point here that I wouldn't trust any
specific benchmark, especially such thorough as "working under NT and
compiling programs, while running Winbecnch".
> can be found on
> http://ixbt.stack.net in the Storage section (Russian only) .
If you want to quote something, please quote the whole URL. My personal
opinion, however, is that "Russian" reviews are tend to be more biased than
in average (not that I'd take any other review for granted). I don't know
which of the article there you had in mind, but from the same site
(http://ixbt.stack.net/storage/hdd-review-66-2.html) one finds that "Так что
еще раз подтверждается - размер буфера не менее важен, чем скорость чтения с
пластины." English translation: "So, it's once again has been confirmed that
the size of buffer is _not_ less important than the data transfer rate off
the plates" (underlining is mine).
> 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 :)
Great :)
> 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 .
Well, isn't that all nothing but an in-depth and lengthy description of word
"quality"?
> 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
In my memory, this happens quite rarely. I did see this a lot for local
reseller's prices, though.
Regards,
Evgeny
--
____________________________________________________________
/ Evgeny Stambulchik <[EMAIL PROTECTED]> \
/ Plasma Laboratory, Weizmann Institute of Science, Israel \ \
| Phone : (972)8-934-3610 == | == FAX : (972)8-934-3491 | |
| URL : http://plasma-gate.weizmann.ac.il/~fnevgeny/ | |
| Finger for PGP key >=====================================+ |
|______________________________________________________________|
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