Question about the difference of IOPS from AWR Reports/ATS(OLT)/IOSTAT

Hi - all.
Anybody know the difference of IOPS from AWR reports and iostat's results?
I used the ATS(OLT) to test the Database's performance in 30mins and found the results in AWR report/ATS(Oracle Loading Testing)/IOSTAT/VMSTAT as below.
Env : DB server: OEL5.6 / Oracle DB:11.2.0.2

Avg         CPU(%)       IOPS(read+write)(MB/S)
ATS         46.094         1.708 #1
AWR        43.8             1.765 #2
IOSTAT     -                 12.028 #3
VMSTAT   47.148 #4         -

the vmstat's result is close to AWR and the ATS(OLT)'s result,however the iostat's result is big different with the AWR and ATS(OLT)'s result.
I know the iostat 's result is the whole server's IO results but didn't find the other process which was started except database's process...