slow zvol performance compared to files on the same pool

[Pete French]

> On 7.x (where ZFS is really quite broken for server use - don't waste 
> too much time on it) the ZVOL code did an "fsync" after every single 
> block write.  Its a testament to your fast disks that you got as high as 
> 12mb/s.  I don't know why your read speed was so bad, but you should try 
> again on 8-current as numerous fixes and improvements have happened.

Ah, thatnks. That explains it perfectly. I'll re-do the read test and
also give 8-CURRENT a try if I get the time. Thanks.

-pete.