same disks:

bash-3.00# iostat -nE
c1t0d0           Soft Errors: 0 Hard Errors: 0 Transport Errors: 0 
Vendor: SEAGATE  Product: ST336607LSUN36G  Revision: 0207 Serial No: 0309A154E6 
Size: 36.42GB <36418595328 bytes>
Media Error: 0 Device Not Ready: 0 No Device: 0 Recoverable: 0 
Illegal Request: 0 Predictive Failure Analysis: 0 
c1t1d0           Soft Errors: 0 Hard Errors: 0 Transport Errors: 0 
Vendor: SEAGATE  Product: ST336704LSUN36G  Revision: 032C Serial No: 0052D1C84Y 
Size: 36.42GB <36418595328 bytes>
Media Error: 0 Device Not Ready: 0 No Device: 0 Recoverable: 0 
Illegal Request: 0 Predictive Failure Analysis: 0

different speed:

bash-3.00# time dd if=/dev/dsk/c1t1d0s0 bs=1048576 count=1000 of=/dev/null
1000+0 records in
1000+0 records out

real    0m29.140s
user    0m0.019s
sys     0m11.241s
bash-3.00# time dd if=/dev/dsk/c1t0d0s0 bs=1048576 count=1000 of=/dev/null
1000+0 records in
1000+0 records out

real    0m15.792s
user    0m0.016s
sys     0m14.391s