On Tue, 2010-08-03 at 17:44 +0300, Avi Kivity wrote: > On 08/03/2010 05:40 PM, John Leach wrote: > > > > dd if=/dev/mapper/zero of=/dev/null bs=8k count=1000000 iflag=direct > > 8192000000 bytes (8.2 GB) copied, 3.46529 s, 2.4 GB/s > > > > dd if=/dev/mapper/zero of=/dev/null bs=8k count=1000000 > > 8192000000 bytes (8.2 GB) copied, 5.5741 s, 1.5 GB/s > > > > dd is just using read. > > > > What's /dev/mapper/zero? A real volume or a zero target? > zero target: echo "0 21474836480 zero" | dmsetup create zero The same performance penalty occurs when using real disks though, I just moved to a zero target to rule out the variables of spinning metal and raid controller caches. John. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
