I have added a new 278GB disk in my server. In fdisk I have created 278GB partition as /dev/sdb1. I did pvcreate and added the disk then created a volume group then created logical volume lv_dbfs, then formatted with mkfs.ext4.
Now I am adding another disk and it is /dev/sdc1, Do i need to format the disk with mkfs.ext4 before extending the volume group or is it not required to format the drive and simply be added to volume group and extending logical volume. I cannot format the drive after extending logical volume. Any help in this will be highly appreciated. Thanks in advance.

You initialize sdc1 with pvcreate. Add it to Volume Group. Then extend logical volume then resize the ext4 fs with resize2fs to use all space.

Precisely to say I have to do these steps
vgextend vg_ora /dev/sdc1
lvextend -L +277G /dev/mapper/vg_ora-lv_dbfs
resize2fs /dev/mapper/vg_ora-lv_dbfs

As the first disk is formatted with ext4,by extending the LV and using resize2fs will be sufficient so there is no need to format as all the remaining space will be in the format ext4 by default. Am I getting it correct? Thanks for the reply

You missed first step of pvcreate with sdc1.

Not necessary unless some non-default PV options are needed. From the vgextend manpage:

"If PhysicalDevicePath was not previously configured for LVM with pvcreate(8), the device will be initialized with the same default values used with pvcreate(8)."