12.7

Storing all blocks of a large file on consecutive disk blocks would minimize seeks during sequential file reads. Why is it impractical to do so? What do operating systems do instead, to minimize the number of seeks during sequential reads?

---

Reading data sequentially from a large file could be done with only one seek if the entire file was stored on consecutive disk blocks. Ensuring availability of large numbers of consecutive free blocks is not easy, since files are created and deleted, resulting in fragmentation of the free blocks on disks. Operating systems allocate blocks on large but fixed-sized sequential extents instead, and only one seek is required per extent.