[MacDV] Re: how and why to benchmark Last one!

[Dmytro Koval'ov]

>>>>> On Wed, 7 Jan 2004, "James" == James Asherman wrote:

  James> A: I do not own Panther(which would be clean) I have dirty old
  James> 10.2.8

Only internal OS disk optimization is not applicable for Jaguar. All
the rest still true.

  James>  B: You are wrong. Speed Disk does not split up files, it
  James> puts them back together and groups like things.  

OK. I am not  sure what prevents you from understanding this stuff, but
I will try to explain it simpler. Speed Disk and alikes work with
things like ''disk sector''. This is a number, that is reported by OS
to SD application. There were times when correspondence between ''disk
sector'' (visible to application) and actual disk sector was
one-to-one. This was time of MSDOS 3.x-5.x and has passed long
ago. This was also possible because under MSDOS application could
access hardware directly. 

This (access HW directly) is *NOT* possible under UNIX. So, what SD
actually sees is some layer of abstraction. This abstraction is
presented to application by OS. And there more such levels. Please
read Peter's mail once again (maybe even twice). I think he has
explained this stuff quite well. 

Nobody can tell for sure that sectors reported to SD with numbers N
and N+1 occupy consecutive sectors (lets say M and M+1) on the same
disk. The thing get even worse if you happen to use any kind of
RAID. These N and N+1 ''sectors'' (in SD terms) can be as well on
different physical disks. But SD will not know that it actually works
with RAID and will try to "fill the holes" and to make contiguous
free space out of them.

So... When you say "SD puts files back together" you are actually
saying is:- "SD puts files on disk in such way, that big files occupy
some space on the disk with consecutive sector numbers. I.e. such
space that looks good in SD drive map."

  James> And you are on the DV list? I'm sorry . 

Yes, I am. And also I am UNIX sys admin and developer. Also I do user
support and I know difference between "system is slow" and "user
reported, that system seems slow today".

  James> Video still likes big
  James> hunks of space all in a row or reported as such. I keep some
         ~~~~~~~~~~~~~~~               ~~~~~~~~~~~~~~~~~~ 

Big chunk of space 

  and

space *reported* as big contiguous space 

are very different things. So, if you think that looking at the nice
contiguous space of lined up rectangles of the same color in Speed
Disk makes you feeling better, than I personally do not mind about
this. 

It will probably make more sence if you'll try to listen to people who
do know HOW things work on computer. Peter was actually citing Apple
regarding de-fragmenting. In this discussion this was the most reliable
reference.

  James> extra because stuff walks in the door.  Now I go back to the
  James> wedding with the defective panasonic tape.

Good luck. Don't forget to de-fragment.

P.S. 

I did have several warnings from iMovie about slow disk. 

Funny thing, that this happened on brand new just few minutes ago
formatted disk (external FW 4500 rpm with OSX10.1.x). I've captured
video to internal drive since then until installed Jaguar. I *never* had
any speed warnings since then. Even though I has never re-formatted or
de-fragmented drive and I (and all my family) do a lot of downloading/
capturing/editing/compiling/whatever on the system.

--Dmytro