Week 1 Flashcards
(18 cards)
What do Linux Files include?
Regular Files
Directories
Special Files (Character or Block)
Pipes
Links(Soft or Hard)
What is a Hard Link?
Another name for an existing File
Points directly to inode of file
If file is moved or deleted, link will still work
What is a Soft Link?
Pointer to a filename
If link is moved or deleted the file won’t work
What is a Block?
Filesystems divide storage space into fixed size blocks
Typical block size is 4096 bytes (4KB)
How is a Magnetic Disk Organised?
Platters - Circular Disks
Read/ Write Heads
For reading and writing, the head senses/ changes magnetism of a sector
How are the platters organised in a Magnetic Disk?
Each platter divided into circular tracks
Each track divided into sectors, each sector has fixed size
Set of all tracks that are above one another makes up a cylinder
How do Magnetic Disks Operate?
Read/ Written by moving arms in/out to required cylinder
All heads/ arms move together
Platters rotate, rotation speed related to transfer rate
What is an SSD?
No moving parts
Instead store data using flash memory
How is an SSD organised?
A controller (Embedded Processor)
Buffer Memory (Volatile Memory)
Flash Memory is divided into pages that are grouped into blocks
What is the Read, Write and Erasing speed of an SSD?
Read - Fast
Write - Fast
Erase - Slow
How is an SSD read?
Copying flash memory into the buffer
Reading data from page in the buffer
How does an SSD get overwritten?
- Copying memory block into buffer
- Erasing block in the flash memory
- Modifying block in the buffer
- Writing block from buffer into flash memory
What are the Fors and Againsts of SSD’s vs Magnetics?
FORS:
SSDs faster than magnetic
More reliable
More power efficient
AGAINST:
More expensive
deteriorate with every write
What is wear levelling?
A process designed to extend life of SS Devices
How does wear levelling work?
Data written on block with lowest erase count
Writing and erasing data evenly distributed. Blocks maximised and fall at same time
What is Dynamic Wear-Levelling?
New data is written to least recently-used block
Avoid wearing out certain blocks by writing to same block again and again
Remaining problem: “cold” data is not m
What is Static wear-levelling?
Same as Dynamic, with few extras:
Periodically moves existing data to least-recently-used block
avoid wearing out certain blocks while block with cold data is never moved
What is the benefit of Wear-Levelling?
A block will fail when it reaches critical number of writes
Thanks to wear levelling, we spread writes evenly among blocks
