On Thu, 5 Feb 2009, Carlos E. R. wrote:-
On Thursday, 2009-02-05 at 18:44 -0000, David Bolt wrote:
If you'd prefer not to use /dev/urandom , you could change the command to if=/dev/zero instead and have the same effect.
In my machine, it is slow and cpu intensive.
Hmm, using /dev/urandom on my machines, the test transfers were done so fast that I couldn't tell whether it was CPU intensive or not. However, re-testing using test blocks of 1MB and a count of 1000 does show it to be CPU intensive and fairly slow using /dev/urandom. Doing the same test using /dev/zero required a significantly larger count for any meaningful measurements. Keeping the 1MB block size and upping the count to 1024000, giving a total transfer of 1,073,741,824,000 bytes, showed that dd may also be fairly CPU intensive using /dev/zero as well. On one system, a 1.6GHz Sempron, dd used 90+% CPU for about 36 seconds and transferred at about 35.5GB/s. On another, a 2.6GHz X2, it took about 23 seconds and used about 50% on each core to transfer at about 46.5GB/s. Purely out of curiosity, I also tested it on my slowest system. That system is an old 300MHz P2 laptop, and it took 71 seconds with the processor at a little under 95%. Its transfer rate was a fraction under 14GB/s. So, end results of this very unscientific test is that using /dev/urandom may be slow and CPU intensive, while using /dev/zero possibly gives very short, and on my systems at least, immeasurable CPU usage spikes. Regards, David Bolt -- Team Acorn: http://www.distributed.net/ OGR-NG @ ~100Mnodes RC5-72 @ ~1Mkeys/s | openSUSE 10.3 32b | openSUSE 11.0 32b | openSUSE 10.2 64b | openSUSE 10.3 64b | openSUSE 11.0 64b | openSUSE 11.1 64b TOS 4.02 | openSUSE 10.3 PPC | RISC OS 3.6 | RISC OS 3.11 -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org