Re: [gentoo-amd64] Re: Is my RAID performance bad possibly due to starting sector value?

[Mark Knecht]

On Sat, Jun 22, 2013 at 6:02 PM, Mark Knecht <markknecht@×××××.com> wrote:

> if what you are suggesting is more like this very short example:
>
> mark@c2RAID6 /VirtualMachines/bonnie $ dd if=/dev/urandom of=urandom1
> bs=4096 count=$[1000*100]
> 100000+0 records in
> 100000+0 records out
> 409600000 bytes (410 MB) copied, 25.8825 s, 15.8 MB/s
> mark@c2RAID6 /VirtualMachines/bonnie $
>


Duncan,
   Actually, using your idea of piping things to /dev/null it appears
that the random number generator itself is only capable of 15MB/S on
my machine.

mark@c2RAID6 /VirtualMachines/bonnie $ dd if=/dev/urandom of=/dev/null
bs=4096 count=$[1000]
1000+0 records in
1000+0 records out
4096000 bytes (4.1 MB) copied, 0.260608 s, 15.7 MB/s
mark@c2RAID6 /VirtualMachines/bonnie $

It doesn't change much based on block size of number of bytes I pipe.

   If this speed is representative of how well that works then I think
I have to use a file. It appears this guy gets similar values:

http://www.globallinuxsecurity.pro/quickly-fill-a-disk-with-random-bits-without-dev-urandom/

   On the other hand, piping /dev/zero appears to be very fast -
basically the speed of the processor I think:

mark@c2RAID6 /VirtualMachines/bonnie $ dd if=/dev/zero of=/dev/null
bs=4096 count=$[1000]
1000+0 records in
1000+0 records out
4096000 bytes (4.1 MB) copied, 0.000622594 s, 6.6 GB/s
mark@c2RAID6 /VirtualMachines/bonnie $

- Mark