Disks; Distributed Systems Tanenbaum ch. 5.4 Distributed Systems Tanenbaum ch. 8.3

Disk Hardware Information written onto the disk in concentric circles At any arm position,each head can read a track All the tracks for a given arm position forms a cylinder

Disk Parameters For the 20GB disk, 281 x 512=140KB/track Transfer a track in 1 rotation time of 8.33ms or a transfer rate of 17 MB/sec 7200rpm

Disk Geometry Virtual Physical Divide the disk into zones with more sectors on the outer zones than the inner zones

Strips and Stripes

RAID Use parallel I/O to improve performance Redundant Array of Inexpensive Disks Organized into 6 levels stripe

RAID Levels Level 3-5

Nested RAID Combine data redundancy and performance of Raid 0 and Raid 1 Raid 1+0 is better for recovery

Comparisons of Multiple CPU Systems

Distributed Systems Multiple complete computers connected by a network Example: our site: blade01, …, blade42, ulab,… are all separate computer systems, but networked together sharing a global distributed NFS file system login onto blade12, look at your login dir login onto ulab, see the same files Distributed system turns a loosely connected bunch of machines into a coherent system

Middleware

Networking Hardware

Networking Services

Network Protocols Protocol- the set of rules by which computers communicate Organize as a stack OSI Layer Example Kind of software (UNIX, Windows) Application Web server, browser User-level Transport TCP Kernel Network IP Kernel Data Link Ethernet Kernel Physical Cat5 cable, etc. Hardware

Interaction of Protocols