FS-A

Extent

Single Extents Allocate files as sequence of contigious disk blocks -> single extent Keep a free list of unused extents on disk Pro Con Easy sequential and random access, few seeks Horrible disk fragmentation, large files difficult to alloc Simple Design Difficult to predict file needs at creation time Multiple Extents Table of base/size pairs (pointers) Pro Con Easy to find free extents Fuller disk -> lot of small extents -> many seeks External Fragmentation

File

Named collection of bytes stored on disk OS View: Ordered set of blocks stored on block device File System: Packs bytes in disk blocks, unpacks on reading