New and old size is same but as i said old hdd crashed so now way to find out format or allocation size@Dj1018 The best bet would be to reach out to Airtel and ask what's the process for replacing the hard disk. They might have a standard operating procedure for these kind of issues.
Having said that, what was the size of the old HDD and what's the size of the new HDD? What partition scheme does it use? MBR or GPT?