File Systems and Disk Layout I/O: The Big Picture

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FFS Cylinder Groups FFS defines cylinder groups as the unit of disk locality, and it factors locality into allocation choices. • typical: thousands of cylinders, dozens of groups • Strategy: place “related” data blocks in the same cylinder group whenever possible. seek latency is proportional to seek distance physical disk sector CPS 210 • Smear large files across groups: Place a run of contiguous blocks in each group. • Reserve inode blocks in each cylinder group. This allows inodes to be allocated close to their directory entries and close to their data blocks (for small files). Sequential File Write write write stall read note sequential block allocation sync read next block of free space bitmap (??) time in milliseconds sync command (typed to shell) pushes indirect blocks to disk 10
physical disk sector 50 MB physical disk sector Sequential Writes: A Closer Look 16 MB in one second (one indirect block worth) 140 ms delay for cylinder seek etc. (???) time in milliseconds Small-File Create Storm inodes and file contents (localized allocation) sync note synchronous writes for some metadata sync delayed-write metadata time in milliseconds longer delay for head movement to push indirect blocks write write stall write write stall sync 11
Page 1 and 2: File Systems and Disk Layout I/O: T
Page 3 and 4: Using Disk Storage Typical operatin
Page 5 and 6: Representing a File On-Disk in Nach
Page 7 and 8: Basics of Directories A directory i
Page 9: The Problem of Disk Layout The leve

File Systems and Disk Layout I/O: The Big Picture

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