I installed second hard drive and formatted it using ivms-4200 . Playback videos don't get deleted any more , new videos are being added . Which makes me think its utilizing scond harddrive automatically . Which is exactly what I have been trying to achieve . Additionally , when I go to menu to select hard drive owerwrite when it full . Number of harddrives is displayed as 2 .
In short , it appears you can add extra harddrive and ivms-4200 , will start using both and switch to empty drive once first one is full . I am going to report back in few month , once both harddrives are overwritten . For now it appears since HD1 was full , it writing to HD2
Thank you for help