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This document, authored by dr. Jiang li from the dept. Of systems & computer science at howard university, provides an in-depth exploration of various aspects of input/output (i/o) systems, focusing on disk systems, dependability, and redundant array of independent disks (raid) technologies. Topics such as bytes/sec and transfers/sec, i/o bus connections, response time, diversity of devices, faults and service interruption, mean time to repair (mttr), mean time between failures (mtbf), availability, disk storage, disk latency, flash storage, flash types, raid 1, 2, 3, 4, 5, and 6, bus types, bus signals and synchronization, interrupts, i/o data transfer, and file system & web benchmarks.
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Dr. Jiang Li
I/O devices can be characterized by
I/O bus connections
Fault: failure of acomponent
A magnetic disk consists of 1- platters (metal or glass disk covered with magnetic recordingmaterial on both sides), with diameters between 1-3.5 inches Each platter is comprised of concentric tracks (5- 30K) and each track is divided into sectors (100 – 500 per track, each about 512 bytes)
Sector ID, data (512 bytes, 4096 bytes proposed), error correcting code(ECC, Used to hide defects and recording errors), synchronizationfields and gaps A movable arm holds the read/write heads foreach disk surface and moves them all in tandem –a cylinder of data is accessible at a time
Average seek time: 6ms Transfer rate: 50 MB/sec Controller overhead is 0.2ms What is the average time to read or write a 512-byte sector for a disk of 10000RPM? Average disk access time = Average seek time + Average rotational delay
Manufacturers quote average seek time
Smart disk controller allocate physical sectors ondisk
Disk/motherboard interface
Disk drives include caches
NOR flash: bit cell like a NOR gate
NAND flash: bit cell like a NAND gate
Flash bits wears out after 1000’s of accesses
Redundant Array of Inexpensive (Independent)Disks
Provides fault tolerant storage system
RAID 0
N + 1 disks
Not widely used
N + 1 disks
Widely used
N + 2 disks
Multiple RAID