Try it the other way round. I guess the data is cached :)
Use bonnie or hdparm -Tt to measure throughput!

Ake wrote:
> Hi!
> After some more experimenting i did the following,
> 
> mkdir /tmpfsdev
> mount -t tmpfs tmpfs /tmpfsdev
> mknod /tmpfsdev/sdb b 8 16 (This is my test disk)
> dd if=/tmpfsdev/sdb of=/dev/null bs=8192k count=20
> 20+0 records in
> 20+0 records out
> 167772160 bytes transferred in 11.006714 seconds (15242711 bytes/sec)
> 
> mkdir /rawdev
> mknod /rawdev/sdb b 8 16
> dd if=/rawdev/sdb of=/dev/null bs=8192k count=20
> 20+0 records in
> 20+0 records out
> 167772160 bytes transferred in 1.668631 seconds (100544793 bytes/sec)
> 
> 
> So tmpfs is the culprit.
> So, yes using udev i DO get a slowdown due to its use of tmpfs.
>