Lecture 10 Flashcards
Operating System Definition:
- Provides an interface for users and applications to access the computer’s hardware.
- Controls access to memory, CPU, HDD/SDD and other peripheral devices connected to the PC.
- Consists of File system, User Interface, and Kernel
Operating System Layers
- User applications
- User mode
- Services
- Application interfaces - Windows Kernel
- Task scheduler
- Memory manager
- File system manager
- GUI manager
- Hardware Abstraction Layer (HAL) - Hardware
File System Definition:
- Used for storing and managing files stored on the PC or on the network to which it is connected.
- Storage organization using hierarchical filing method using folders and files
Hierarchical Filing Syntax and Definition:
- Folders/subfolder(s)/subfolder(s)/file(s)
- Can be accessed through GUI or CLI (terminal)
File Index System:
- The OS maintains a database of files and locations
- This db is updated as files are created, modified or deleted.
- Helps users search for files by simply knowing a part of the name only or type.
User Interface:
- An interface for interacting with the contents in storage.
- Can be Graphical (GUI) or text-based (CLI / terminal)
- Associates file types with applications or actions,
For instance, with GUIs you double click a document to open
Kernel
- Schedules processes and tasks onto the CPU, taking priorities into consideration.
- Manages memory allocation, ensuring that two apps. do not simultaneously try to assess the same memory space.
- Interfaces with the hardware
Client vs Server OS:
- Mostly the same, except that server OS can handle more service requests and of varied types.
The server OS can also run client applications, such as MS Excel.
Servers also can also run client variants of certain services, such as DHCP client – because like clients, they also can be configured to use dynamic IP addresses.
Client vs Server OS example:
Example: Active directory, DHCP, DNS, RADIUS etc.
Server OS use cases
AAA - User authentication, authorization and accountability
(radius server, TACAS+)
Managing user accounts & policies in a domain: Active Directory Server / Access control
- For access control and policy management. (no web browsing during work hours, or no flash drives enabled/allowed)
- Access to printer or R/W/F access on files
Active Directory Server / Access control is windows based and runs on:
Linux equivalent runs on:
LDAP
Lightweight Directory Access Protocol
Network Information System (NIS)
NAS acronym:
Network attached storage
NAS definition:
- A dedicated server device designed for providing shared storage for network users.
- Can also be A regular Windows server hardware running a NAS software
- it is a SINGLE device
- Usually connected to the network via Ethernet
- Can be integrated with Windows AD for AAA
NAS consists of a bunch of disks which appear to users as network mounted volumes. The disks can be configured using different types of ___.
RAID config.
- Can be integrated with Windows AD for AAA
- Relatively inexpensive and easy to setup
- Usually connected to the network via Ethernet
Raid definiton
Redundant Array of Independent Drives or Redundant
Array of Inexpensive Disks
RAID 0:
Striping:
- Combines all the disks together with all
appear as one entity to users. - Easy to setup and makes FULL use of all the disk space.
RAID 1
Mirroring:
the set of disks are split into 2 halves with each
mirroring the other
Better redundancy but scarifies half the total storage size
RAID 5
Striping + Parity:
- Requires minimum of 3 disks.
- Data is striped across the disks, but the
equivalent of 1 disk is used for parity
checksum. - Parity checksum is used for error detection
and to help recover / rebuild data in case of
loss of 1 disk
RAID 6
Striping with double parity
Can survive loss of 2 disks
RAID 10 – Raid 0 + Raid 1
Splits into two halves (Raid 1)
- Strips data across the disks in each half (Raid
0) - Only half the total disk space is usable.
- If one half is lost, data can be copied from the
surviving half
SAN acronym:
Storage Attached Network
SAN definition
Designed for providing storage solutions to networked users.
Targeted at servers rather than clients*
Super high-speed, very low latency BUT super expensive
Enterprise level usage
- SANs usually runs on what cable? Speeds up to what amount?
fibre optic, hence 100s of videos can be used simultaneously with speeds of up to 10Gb/s
Easy to scale up, which is a major advantage over NAS
Availability definition
Availability is the minimal interruption to service, i.e., minimal downtime
It is measured in 9s
High Availability definition
High Availability is the percentage of time the network is available.
It is measured in 9s
How many hours of downtime per anun with a network availability of 99.9%?
approx. 9 hours downtime per annum
How many hours of downtime per anun with a network availability of 99.99%?
approx 1 hr downtime per annum
How many hours of downtime per anun with a network availability of 99.999%?
approx 5 mins downtime per annum
How many hours of downtime per anun with a network availability of 99.999999%?
approx. 316ms downtime per annum – AWS S3 storage
Fault tolerance definition:
Fault Tolerance is the ability to withstand fault and continue to function as expected. Aka zero service interruptions.
Achieved using redundancy (back ups)
Redundancy definition:
A fault tolerance method
Used for fail-over – where another takes over when the primary (active) fails
Hot-swappable – devices or components can be removed, added or replaced while the server is running.
Example mouse/kb.
Some high-end servers support hot-swappable disks, memory and even CPU * Hot-swappable is called “hotplug” in Linux world
Server clutering
a type of redundancy
two or more servers configured to work together as a single entity.* Both are exact replica and can be running simultaneously or in active/passive mode
Redundancy - load balancing
load balancing – where tasks are split across both servers, thus improving performance.
raid is a form of
redundancy
