Because creating a pool can fail unexpectedly in different ways, and because formatting disks is such a potentially harmful action, the zpool create command has an additional option, -n, which simulates creating the pool without actually writing to the device. This option performs the device in-use checking and replication level validation, and reports any errors in the process. If no errors are found, you see output similar to the following:
# zpool create -n tank mirror c1t0d0 c1t1d0 would create 'tank' with the following layout: tank mirror c1t0d0 c1t1d0
Some errors cannot be detected without actually creating the pool. The most common example is specifying the same device twice in the same configuration. This error cannot be reliably detected without writing the data itself, so the create -n command can report success and yet fail to create the pool when run for real.