I've a question is it possible to connect the Chromecast with an USB Hard Drive via micro USB OTG Y cabel?
Currently Chromecast can only use USB OTG for firmware flashing. OTG isn't available in the normal booted state.
So if you're asking whether you can connect a USB hard drive on a USB OTG cable connected to Chromecast for playing/accessing stuff on it, No.
If you're trying to use a USB hard drive for FlashCast ROM/mod flashing, I'm not sure if that will work.
In either case, you need a powered OTG cable, as Chromecast does not provide power on the USB - it expects to receive it there.