Hi Adam,
You have pointed me to the answer. when I did the df -hA command it showed the aggr total space as 4275Mb with 570Mb used and 3704Mb available. The virtual disks in the simulator are smaller than I expected and I misread the available space first time round, assuming I had 4.2Tb not 4.2Gb. I was trying to create a flexvol of 100Gb. I destroyed the two volumes in the aggr and successfully created new ones at 100mb each.
I did try 100Mb volumes when I first brought up the simulator but I think the disks had not zeroed correctly then so I started again. Anyway, I now have disks - thanks for taking the time to reply.
Peter