Re: random_page_costs - are defaults of 4.0 realistic for SCSI RAID 1

On Wed, Sep 12, 2007 at 12:02:46AM +0100, Gregory Stark wrote:
> "Decibel!" <decibel(at)decibel(dot)org> writes:
>
> > On Tue, Sep 11, 2007 at 02:49:28PM -0400, Jean-David Beyer wrote:
> >> It is tricky for me to find a big enough file to test. I tried one of the
> >
> > dd if=/dev/zero of=bigfile bs=8192 count=1000000
>
> On linux another useful trick is:
>
> echo 1 > /proc/sys/vm/drop_caches

The following C code should have similar effect...

/*
* $Id: clearmem.c,v 1.1 2003/06/29 20:41:33 decibel Exp $
*
* Utility to clear out a chunk of memory and zero it. Useful for flushing disk buffers
*/

int main(int argc, char *argv[]) {
if (!calloc(atoi(argv[1]), 1024*1024)) { printf("Error allocating memory.\n"); }
}
--
Decibel!, aka Jim Nasby decibel(at)decibel(dot)org
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