[RndTbl] ZFS I/O strangeness

[Trevor Cordes]

On 2012-03-03 Adam Thompson wrote:
> I have a ZFS RAIDZ3 filesystem under OpenSolaris (actually a Nexenta
> build so a GNU userland on top of OpenSolaris kernel).
> 
> "dd if=filename of=/dev/null bs=8k" gives me ~66Mbytes/sec.
> "cat filename | dd of=/dev/null bs=8k" gives me ~142Mbytes/sec.

Adam, you said you get optimal speed at 8M but your examples shows 8k!
The above makes perfect sense as cat will use ibs>8k and dd is using
8k.  I bet you'd get 142 if you did for the dd ibs=1M obs=8k, which is
probably what the cat line is doing behind the scenes.  Methinks your
problem was a typo.