Re: Why actual speed is slower than nominal? (2.6x vs 4x)
Hi,
> I am curious as to why the actual speed I get happens to be a lot
> slower than the nominal one.
> If I do not use "hdparm" to set the speed of /dev/hdd to udma2, then
> actual speed happens to be even slower.
> /dev/cdrom1: "Current Write Speed" is 4.1x1385KBps.
> builtin_dd: 2011280*2KB out @ average 2.6x1385KBps
I got a similar slowdown (3.4x rather than 4x) which is clearly due to
a lack of filesystem throughput on the input side. My system is a
AMD 2600+ with a cheap mainboard and a disk of medium performance.
> I am creating the image on the fly, could that make things go slower?
Yes and no.
If you have mkisofs write into a buffer file and have
growisofs write that buffer to DVD you will probably see
full speed.
But a buffered write will not need less time than a write
on the fly because you will need more time buffering than can
be saved by full DVD speed.
Nevertheless such a buffered write would probably prove that
there is no problem with growisofs and the DVD writer. At least
it did for me.
Have a nice day :)
Thomas
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