[TriLUG] OT: hd speed with 33MHz and 100MHz controller are the same

[Ben Pitzer]

So where would you expect the data to be cached?  Even if it's cached in
memory, it still has to write it over that 33MHz wire to the disk.  The disk
cache is only for staging data before it actually makes it out to the
platter, so once it's gone to disk it's forgotten.  No, basically, if it's
only got a 33MHz pipe channel between the bus and the proc, that's as good
as you're going to get.  I wouldn't be surprised that the machine is doing
everything else just fine, and that bus is the only bottleneck you're
getting.

-Ben Pitzer


On 6/13/07, Joseph Mack NA3T <jmack at wm7d.net> wrote:
>
> On Tue, 12 Jun 2007, Robert Dale wrote:
>
> > The bus probably is 33MHz, 66MHz at most.  And it probably is the
> bottleneck.
> > Just as you wouldn't expect to Gb speeds on a 10baseT network just
> > because you plug in a GigE card.
>
> I hadn't realised there was as much happening between the
> CPU and the disk. Since badblocks is writing the same data
> over and over, I would have thought it would all be cached.
>
> It's taken overnight to write the first 0xaaaaaaaa bits to
> the disk. It's just started to read them back. It will be 4
> days before its finished my new 320G disk at 33MHz.
>
> > A better benchmark would be to use something like bonnie++ [1] on each
> > disk separately and compare numbers.  It measures raw throughput
> > through various tests - it does not try to verify data like badblocks
> > (which potentially could be cpu bound).  You can also limit the size
> > of files.
>
> will give it a go in 4 days ;-) thanks
>
> Joe
>
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> Joseph Mack NA3T EME(B,D), FM05lw North Carolina
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