Block Alignment and Unaligned I/O Overhead

Write a C program that demonstrates the cost of unaligned I/O.

Requirements:

• Define a block size of 4096 bytes
• Simulate writing 8192 bytes (2 blocks) under three scenarios:
  • Aligned: offset=0, size=8192 — 2 full block writes
  • Offset-unaligned: offset=1024, size=8192 — spans 3 blocks, first and last are partial
  • Size-unaligned: offset=0, size=9000 — spans 3 blocks, last is partial
• For each scenario, calculate:
  • Number of physical blocks touched
  • Number of full block writes
  • Number of read-modify-write operations
  • Total bytes read from disk (for RMW)
  • Total bytes written to disk
  • Write amplification factor: total bytes written / user bytes requested
• Print a comparison table
• Include a note about Direct I/O (O_DIRECT) and why it requires aligned buffers
• Explain why databases use posix_memalign for I/O buffers