Chapter 11: Hard Drive Technologies

composed of platters with read write heads on actuator arms

aluminum coated with magnetic medium

HDD

HDD
tiny magnetic fields

switch north and south polarity back and forth

groups of flux reversals

any combination of 1 and 0's can be stored in preset combination

15 different runs

HDD reads them as groups, resulting in faster and denser data

best guess

16 to 20 fluxes

hard drives that store their fluxes vertically

1 terabyte sizes

determines where a hard drive stores data

2 heads per platter

each group of tracks of the same diameter

number of sectors in each track

split like a cake

no moving parts

usb thumb drives
cameras

more expensive than HDD

hard drives

PATA
SATA

parallel ATA

send data in parallel
40 or 80 wire data cable

serial ATA

drives that send data in serial
using only one wire for data transfers

master/slave jumpers to differentiate between the two drives

used existing AT BIOS on a PC

built in controller

higher capacities
support for non hard drive storage devices
support for 2 more ATA devices for a maximum of 4

logical block addressing

way to get by HDD size limits

SMART (hard drive check)

ultra DMA

hard drives communicates with the PC

completely ignoring the CHS values

feeding the LBA a stream of addressable sectors

137 GB

less cables
better cable control
much faster

auto runs the Hard drive for install

external SATA
2 meter cable

connect together in a string of devices called a chain

putting something on the ends of the wires to prevent echo

writing data on two drives

a primary and a back up

separate controller for each 2 drives

system will continue to operate even if the primary drives controller stops working

spreading the data among multiple drives


only advantage is speed

if either drive fails ALL data is lost

protects data by adding extra information (parity data)

majority of network severs

6 levels of raid
0 - disk stripping
1 - disk mirroring \ duplexing
2 - disk stripping with multiple parity drives
3 and 4 - disk stripping with dedicated parity
5 - disk stripping with distributed parity
6 - disk stripping with extra parity

disk stripping
2 drives
no redundancy to data
one fails all is lost

disk mirroring duplexing

ultimate in safety
lose storage space since data is duplicated

disk striping with multiple parity drives

ignore this

disk stripping with dedicated parity

disk stripping with distributed parity

most common

distributes data and parity information evenly across all drives

disk stripping with extra parity

is raid 5 with extra parity

larger arrays

SDD - less energy, smaller, noiseless, nonvolatile flash memory

more expensive

retrieve data faster
slower write time