1.Contiguous Allocation(连续分配)ll Advantages: Support both random sequential access Start block:b; Logical block number:i =physical block number:b+i Fast access speed,because of short head movement 多 Disadvantages: External fragmentation Wasteful of space (dynamic storage-allocation problem). Files cannot grow, or File size must be known in advance. Internal fragmentation 4口”4814在，4色，主)QC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Contiguous Allocation (连续分配) III ▶ Advantages: ▶ Support both random & sequential access ▶ Start block: b; Logical block number: i ⇒physical block number: b + i ▶ Fast access speed, because of short head movement ▶ Disadvantages: ▶ External fragmentation ▶ Wasteful of space (dynamic storage-allocation problem). ▶ Files cannot grow, or File size must be known in advance. ⇒Internal fragmentation
Extent-Based Systems Many newer file systems(l.e.Veritas File System)use a modified contiguous allocation scheme Extent-based file systems allocate disk blocks in extents An extent is a contiguous block of disks Extents are allocated for file allocation A file consists of one or more extents. 4口”4814在，4色，主)QC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Extent-Based Systems ▶ Many newer file systems (I.e. Veritas File System) use a modified contiguous allocation scheme ▶ Extent-based file systems allocate disk blocks in extents ▶ An extent is a contiguous block of disks ▶ Extents are allocated for file allocation ▶ A file consists of one or more extents