@Rupak Chakraborty following are the suggestion:- 1) 64-bit guests need hardware-virtualzation enabled in the hosts bios. Enable Intel VT-x/AMD-V from BIOS. 2) when creating the 64-bit guest you must select 64-bit in General -> Basic -> version. 3) Try with other version of OS. ... View more

Foowloing are the changes in cent os 7 :- New initialization system, systemd. New firewall control, firewalld. This adds a more dynamic and flexible way to control the firewall module in the kernel, which is still netfilter. New bootloader. GRUB2 adds rich scripting support as well as support for the new hardware options offered on modern mainboards. New default filesystem, XFS. XFS adds support for larger single filesystems, faster format times (0 seconds), integrated snapshots, and live filesystem dumps for backup without first unmounting. GNOME 3 – This only really applies to those who use RHEL/CentOS in the desktop, like me. As with any other distro, you aren’t locked into GNOME 3. I personally like it, but KDE is readily available and others can be found on EPEL. If you are used to previous versions you may want to stick with 6. 7 has a lot of command changes And in our env we are using Cent OS 7. Still Didn't face issue with performance etc.. ... View more