Module 4: Intelligent Storage Systems (Components) Flashcards
What are the two key functional components of ISS?
disk controller
storage device
What are the characteristics of a storage controller in an ISS?
ISS typically has more than one controller
controller has one of more processors and cache memory for IO requests
connected to compute system either directly or through storage network
How do storage controllers work in an ISS?
receive IO requests from compute system that are read or written from or to storage by the controller
What is a hard disk drive?
persistent storage device that uses rapidly spinning disk or platter coated in magnetic material to store data
How are IO operations performed on an HDD?
performed by rapidly moving arm across spinning disks/platters
How is data transferred in an HDD?
done between disk controller and platters through read/write head attached to the arm
How is data recorded on a platter?
recorded on binary code
What is a head disk assembly (HDA)?
case that the set of platters is in
How is data encoded onto the platter?
polarizing magnetic material on both sides of the platter - data can be written/read on both sides also
What determines drive capacity?
number of platters
storage capacity of each platter
What is a spindle?
connects all platters together - connected to the motor which rotates at constant speed
What is RPM in an HDD?
rotations per minute
How does the R/W Head work?
senses magnetic polarization but never touches platter - maintains microscopic air gap in between called “head flying height”
air gap removed when spindle stops spinning and R/W head rests on landing zone
How are R/W Heads mounted?
on the actuator arm assembly - positions R/W Head on part of platter where data must be read or written
R/W heads for all platters are attached to one actuator arm assembly and move across platters simultaneously
What is the controller in an HDD?
printed circuit board mounted at the bottom of the drive
What are the parts of the controller in an HDD?
microprocessor
internal memory
circuitry
firmware
What does the firmware do in the drive controller?
controls power and speed motor
manages communication between drive and compute system
controls R/W operations - moves actuator arm and switches between different R/W heads
What are the factors that affect drive performance?
seek time
rotational latency
data transfer rate
What is seek time?
time it takes to position R/W heads across platter with a radial movement
aka time taken to position and settle arm and head over the write right track
What is the relationship between seek time and performance?
lower the seek time the faster the IO operation
What is rotational latency?
time taken by the platter to rotate and position data under the R/W head
How is data accessed on a HDD?
actuator arm moves R/W head over platter to particular track
platter spins to position requested sector under R/W Head
What is rotational latency dependent on?
rotation speed of spindle - measured in milliseconds
How is a read operation performed on an HDD?
data first moves from disk platter to R/W heads - than moves to drives internal buffer
data moves from buffer through the interface to the HBA on compute system
What is data transfer rate?
average amount of data per unit time that the drive can deliver to the HBA
How is disk service time calculated?
seek time + rotational latency + data transfer rate
How does disk controller utilization impact IO response time?
As utilization grows response time slows - IO requests become serialized in a waiting line - completed one at a time in order
What are SSDs?
devices that use non-volatile flash storage for persistent storage - available with same interface as HDDs but consume less power
What are the internal components of an SSD?
IO Interface
Controller
Mass Storage
What is the IO Interface in an SSD?
connects the power and data connectors to the SSDs
What is the controller in an SSD?
manages all drive functions - consists of drive controller, RAM and NVRAM
What is the NVRAM in an SSD controller used for?
to store the SSDs operational data and software - not all SSDs have separate NVRAM
What is the RAM in an SSD controller used for?
used in management of data being read and written from the SSD as a cache and for SSDs operational data and software
What is mass storage in an SSD controller used for?
an array on nonvolatile memory chips - retains the contents when powered off - chips called flash memory - number of chips related to drive’s capacity
What are some characteristics of SSD performance?
perform better random reads
use all internal IO channels in parallel for multi-threaded large block operations
best for workloads w/ short burst of IO activity
What does SSD performance depend on?
access type
drive state
workload duration
What is the effect of SSDs being random access devices?
SSDs pay no penalty for retreiving IO - gives them a much higher response time than HDD
What effect does high capacity utilization have on SSDs?
take longer to complete read write cycle
What is the best environment to run SSDs?
carefully tuned multithreaded small-block random IO workload storage environments
What is the goal of Moore’s law when it comes to storage?
something that has the speed of DRAM but cost of NAND memory
