What is Indexed File Allocation Scheme?
In file allocation, we maintain the allocation table for all disk pointers. Indexed file allocation reduces this overhead. Instead of keeping a file allocation table with all disc pointers, the Indexed allocation technique saves all disc pointers in one of the blocks known as an indexed block. The indexed block does not contain file data but rather links to all disc blocks allocated to that specific file. The index block address will be the sole thing included in the directory entry.
Now, let’s learn some advantages and disadvantages of Indexed file allocation.
Advantages of Indexed file allocation
There are multiple advantages to Indexed file allocation. Some of them are as follows:
- This allows for direct access to the file's occupied blocks, allowing for quick access to the file's blocks.
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It solves the issue of external fragmentation.
External Fragmentation: When a dynamic memory allocation mechanism allocates some memory but leaves a small portion of memory unusable, this is referred to as external fragmentation. If there is too much external fragmentation, the amount of usable RAM is significantly reduced. There is sufficient memory space to perform the request, but it is not contiguous.
Disadvantages of Indexed file allocation
Now, let’s look at the disadvantages of indexed file allocation.
- A faulty index block could result in the loss of the entire file.
- The pointer overhead for indexed allocation is larger than the pointer overhead for linked allocation.
- Having an index block for a small file is entirely unnecessary.
- More overhead with the pointer.
- In the case of very small files, like those that extend only 2-3 blocks, the indexed allocation would keep one complete block (index block) for the pointers, which is inefficient in terms of memory consumption. However, in linked allocation, we lose only one pointer per block.
Limitation of FAT
The FAT file system, though simple and widely compatible, has significant limitations. It imposes size limits on files and partitions, with FAT32 capped at 4 GB per file and 8 TB per partition. Its fixed cluster sizes can lead to inefficient space use. FAT lacks advanced features like journaling, file permissions, encryption, and compression, making it less secure and reliable. It is prone to fragmentation, which degrades performance, and has limited support for metadata and extended attributes. Due to these constraints, FAT is less suitable for modern, complex applications but remains popular for removable media.
Frequently Asked Questions
What are various file allocation methods?
There are three types of file allocation methods: Contiguous allocation, linked allocation, and indexed file allocation.
What is the difference between linked file allocation and indexed allocation?
The major difference between them is that Linked file allocation does not allow random access, whereas indexed allocation does.
What are the benefits of indexed allocation?
Indexed allocation benefits include improved file access speed and efficiency by storing all block addresses in a single index block. It eliminates external fragmentation and simplifies file growth, as blocks can be non-contiguous. This method enhances random access performance and simplifies file management.
Why do we need indexed file allocation?
We need indexed file allocation because There was a requirement for an allocation approach that would allow disc blocks to be utilized effectively while simultaneously reducing the access time.
Conclusion
This article extensively discussed Indexed File Allocation. We learned the concept behind it and its advantages and disadvantages.
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