Am Sonntag, 7. Februar 2010 schrieb Mark Knecht:

> Hi Willie,
>    OK - it turns out if I start fdisk using the -u option it show me
> sector numbers. Looking at the original partition put on just using
> default values it had the starting sector was 63 - probably about the
> worst value it could be. As a test I blew away that partition and
> created a new one starting at 64 instead and the untar results are
> vastly improved - down to roughly 20 seconds from 8-10 minutes. That's
> roughly twice as fast as the old 120GB SATA2 drive I was using to test
> the system out while I debugged this issue.

Sorry if I reheat a topic that some already consider closed. I used the 
weekend to experiment on that stuff and need to report my results. Because 
they startle me a little.

I first tried different start sectors around sector 63: 63, 64, 66, 68 etc. 
They showed nearly the same results in speed. So I almost thought that my 
drive, albeit being new and of high capacity, is not affected by this yet.

But then I tested my main media partition, which starts in the middle of the 
disk. I downloaded a portage snapshot and put it into a ramdisk, so reading 
it would not manipulate measurements. I also copied a 1GB file into that 
ramdisk to test consecutive writes.

As a start sector I chose 288816640, which is divisible by 64. The startling 
result: this gave the lowest performance. If the partition starts in one of 
the sectors behind it, performance was always better. I repeated the test 
several times to confirm it. How do you explain this? :-?

The following table shows the ‘real’ value from the output of the time 
command. SS means the aforementioned start sector with SS % 64 == 0.

action         SS (1st)   SS (2nd)   SS+2       SS+4       SS+6       SS+8
-------------+----------+----------+----------+----------+----------+----------
untar portage  3m12.517   2m55.916   1m46.663   1m35.341   1m47.829   1m43.677
rm portage     4m11.109   3m54.950   3m18.820   3m11.378   3m21.804   3m12.433
cp 1GB file    0m21.383   0m13.558   0m14.920   0m12.813   0m13.407   0m13.681

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