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A comprehensive overview of data storage and disk access concepts, covering topics such as memory hierarchy, hard disk drives (hdds), solid-state drives (ssds), buffer management, and disk scheduling algorithms. It includes detailed explanations, examples, and complete solutions to exercises, making it a valuable resource for students studying computer science or related fields.
Typology: Exams
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Data Storage and Disk Access involves what?- Memory Hierarchy
Persistent StorageNon-volatile storage on a secondary storage medium such as a hard disk.
Transfer of data from memory to storage is very ________-__________. It requires_________ management and includes a ___________ time consuming careful buffer Volatile Memory consists of:SRAM: registers and L1, L2, and L3 caches
What are the 2 main types of secondary memoryHDD and SSD
HDD and their propertiesHard disk drive
Persistent Memory consists of:Non-volatile RAM: NVM, NVRAM, SCM NVMNon-volatile memory
NVRAMNon-volatile RAM
SCMStorage Class Memory
Characteristics of NVRAM:- Byte-addressable
In-Memory DBMS:______ _____ of DRAM allows for large _______ ________ to store entire (or at least working) DB
In-Memory DBMS implications1. No I/O during execution of transactions
Can In-Memory DBMS make use of persistent memory still?Yes
Traditional DB requires both....persistent memory working/transient memory _____________ are performed on data as it's transferred from ________ to ________________ Operationsdisk to main memory
arcs called __________concentric rings called tracks called sectors Sectors contain ________ sequence of _________contiguous, bytes
Cylinderset of tracks with same diameter on all surfaces
BlocksUnits which are read from OR written to
When disk is formatted, the block size is set to... Otw block size is ______a small number of sectors (4 - 16 kB) 4 kB Blocks are separated by...fixed sized gaps which contain ctrl info
Blocks can be addressed by...1. Cylinder #
Visually explain writing data to a disk1. New record from main memory
Disk head for each ___________surface
Do disk heads move separately or together?separately
Disk head arrayDisk heads move together in identical positions respective to their surfaces
Where must a disk head be in order to read/write a blockover it
Can multiple disk heads read/write simultaneously?No, only one at time
Time to access a block on a disk is composed of:1. Seek time
Average Rotational Delay0.5 * MAX(rotational delay)
Transfer time depends on...Request size
Transfer time for entire track(1 000ms * 60s) / disk rpm for the entire track
Transfer time for one block(1 000ms * 60s) / disk rpm / blocks per track
Minimum Seek Time 0 Disk head is on the desired track Maximum Seek TimeTime to move from innermost to outermost track
Average Seek Time
1/3 maximum seek time NOT 1/
Does practice head move at constant speed?In practice no, it accelerates/decelerates
Access Time Comparison Reorder Register, DRAM, and Cache in transfer of data speed b/w main memory and x Fastest to SlowestRegister CacheDRAM
Reducing Disk Access TimeStore related data in close proximity there are milliseconds of difference b/w accessing 2 records in adjacent blocks vs ondifferent tracks
Example methods of buffering Data1. Prefetching
FIFOFirst-come-first-served Processes requests in order in which they are received Elevator and variantseg: SCAN, LOOK, C-SCAN, C-LOOK Requests buffered and disk head moves in ONE directions processing requests Arm then reverses direction and processing requests in the opposite direction Does FIFO or Elevator algo generally perform better?Elevator
Shortest-seek...
Goals of Disk Scheduling Algorithms1. Reduce overall access time
Types of Disk Failures- Intermittent
