Final answer:
Indexed allocation for large files is handled through linked schemes, multilevel indices, or a combined scheme, where index blocks are either linked, hierarchically arranged, or both to efficiently manage file pointers when a single index block is insufficient.
Step-by-step explanation:
When dealing with indexed allocation in file systems, it's necessary to handle cases where index blocks become insufficient for large files. There are three broad mechanisms to address this challenge:
- Linked scheme: In this method, additional index blocks are linked together like a linked list. When the initial index block is full, a pointer at the end points to another index block, allowing a file to continue expanding across multiple index blocks.
- Multilevel index: This approach creates a hierarchy of index blocks. A single index block points to secondary index blocks, which in turn point to the actual data blocks. This multilevel indexing can expand dynamically and accommodate very large files.
- Combined scheme (also known as the indexed-linked scheme or inline extent): This combines direct pointers with indirect pointers. Some number of direct pointers are used for the initial blocks of the file, and when direct pointers are exhausted, an indirect block of pointers is used. This method is often seen in modern file systems because it provides a good balance between fast access to small files and expandability for large files.
All these mechanisms aim to manage large files efficiently when a single index block can't hold all the file pointers needed, and each has different advantages in terms of complexity and access speed.