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 and with the disk spinning, each head can read a track Each track is divided into user accessible data areas(contain 512 bytes) called sectors. 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