@Preetam Nahak - Welcome to Microsoft Q&A and thanks for reaching out to us.
If you have a retention period of 2 days and you have enabled daily backup of Azure disk, then the first backup snapshot (full) will be deleted after 2 days. If you try to restore your data after 3 days, you will not be able to restore the entire data as the first backup snapshot (full) will not be available. You will only be able to restore the data that was backed up in the last 2 days.
Please take a look at this doc for more information: https://learn.microsoft.com/en-us/azure/backup/restore-managed-disks
Hope this helps. and please feel free to reach out if you have any further questions.
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