I have Intel S2600GZ server with 1 SSD (on which OS will be installed), 2 SAS hardisks & RS2WC040 RAID controller, I have to created RAID 1 on SAS. but it's not detecting SSD on which I have to install OS.
Based on the information provided, the Intel® RAID Controller card RS2WC040 only has 1x SAS channel that would support the first 4 drives on the side of the backplane where you plug in the cable that goes from the RAID controller to the backplane.
If you inspect the connectors of the backplane (see example), you will see that there is more than one SAS connector. Each one of them would support up to 4 drives.
In this case, I would suggest moving the drive to the other side, where the other 2 drives are installed or you may also consider installing the SSD internally as the example listed below.
If you prefer to run your Operating System through the hardware RAID solution, you may also considering using the Intel® RAID Controller RS2WC080 instead.