What is Volume header?
Volume headers are the index of every Volume which is available on that hard drive. Each individual hard drive Volume contains a separate Volume header or a group. Before getting into the details of Volume headers two things has to be cleared; hard drive Volumes and Headers.
An individual hard drive partition with a single File system is called as hard drive Volume.
Header is like an index of a book. Whenever a scan process is initialized by the BIOS or by the operating system, the index pointers will look at the MBR - Master Boot Record, regarding the number of drives. And only after that the MBR will point to the Volume headers.
What is the use of Volume Headers?
Though the hard drive looks larger, spatially it is made up of small bits and bytes of memory spaces grouped as sectors and tracks. For the least even to store a very small data, it will take lots of bits and bytes. And the data won’t be ordered and grouped in individual separate locations. They are stored where ever space is available and this information will be stored in the form of hash tables on your hard drives. Volume headers direct the pointer programs to fetch the correct data in that particular hard drive Volume.
What is the size of a Volume header?
The Volume headers size will be less than 1000-kilo bytes. As they have information regarding only the hard drive Volume structure, the size will be negligible. Some of the information types that the Volume header holds are below.
The info may vary accordingly based on operating system and file systems.
When is it created?
Normally, these Volume headers are created at the time of OS installation, particularly while formatting the Volume and is done by the operating system.
What happens if a Volume header is corrupt or deleted?
Whenever a Volume header fails to provide information to the index pointers it throws an error. These errors regarding Volume header can be repaired by reinstalling the operating system or reformatting your hard drive. While doing this, you may lose all your data inside the Volume. So be careful while handling these Volume errors. Refer the link for reformatted hard drive recovery if you have lost data after reinstalling or reformatting of hard drive.
Some samples of error messages found on Mac operating system are mentioned here...