Flashcards
Hardware and Redundancy
Flashcards do conjunto (16)
- 1What is the difference between a switch, a hub and a router?Hub replicates signals L1;
Switch forwards packets based on MAC addresses (intranet)L2 ;
Routers forwards packets based on IP addresses (internet) L3. Usually routers also have DHCP server and NAT service and Wifi broadcast - 2Explain a hard diskA hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that uses magnetic storage to store and retrieve digital information using one or more rigid rapidly rotating disks (platters) coated with magnetic material. The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a random-access manner, meaning that individual blocks of data can be stored or retrieved in any order and not only sequentially. HDDs are a type of non-volatile storage, retaining stored data even when powered off.
- 3Explain a CPUA central processing unit (CPU), also called a central processor or main processor, is the electronic circuitry within a computer that carries out the instructions of a computer program by performing the basic arithmetic, logic, controlling, and input/output (I/O) operations specified by the instructions.
- 4Explain a RAMRandom-access memory (RAM) is a form of computer memory that can be read and changed in any order, typically used to store working data and machine code. A random-access memory device allows data items to be read or written in almost the same amount of time irrespective of the physical location of data inside the memory. It is the physical hardware inside a computer that temporarily stores data, serving as the computer's "working" memory. Additional RAM allows a computer to work with more information at the same time, which usually has a considerable effect on total system performance.
- 5Explain a flash memoryFlash memory is an electronic (solid-state) non-volatile computer memory storage medium that can be electrically erased and reprogrammed. It is often found in USB flash drives, MP3 players, digital cameras and solid-state drives.
- 6What type of connector does an Ethernet cable normally have?RJ45
- 7What is fibre optics?Fibre optics are a newer form of connector used for data transmission, using very thin glass tubes and passing data over light. They have several significant advantages over copper lines like higher bandwidth, longer distance transmission, far fewer ways of signal disruption, etc.
Data is transferred by light, so fibre optics use a LED (Multimode) or Lasers for longer distances. Usually needs a repeater every 100Kms. Under the sea the cable is covered by a steel protecting enclosure and a copper surrounding to transmit electricity to the repeaters. Fibre optics cables have no interference from the outside world, unlike copper cables. - 8What are LACP and link aggregation?LACP is Link Aggregation Control Protocol and teams multiple ports on a Switch or device to a logical one with increased bandwidth. The protocol also allows redundancy if one of the cable (copper/fibre) is disconnected, the link is still up but the bandwidth is decreased by the factor of the disconnected port.
- 9What is a console server used for?A console server (also referred to as console access server, console management server, serial concentrator, or serial console server) is a device or service that provides access to the system console of a computing device via networking technologies.
- 10Can two different networks be connected to the same switch?Yes, there can be multiple networks on a single switch, in the form of VLANS.
- 11What is the difference between a layer 2 and a layer 3 switch?Layer 2 is just interested in MAC/Ethernet L2 and is unable to do any IP related functions like routing
L3 Switch is basically a router, it is able to perform routing via IP and allows to use sophisticated routing protocols. OSPF, RIP can be used to route traffic on different connections and routes. - 12What is the difference between a hot stand-by setup and load-balancing?Hot Standby: Software components are installed and available on both primary and secondary nodes. The software components on the secondary system are up but will not process data or requests. Data is mirrored in near real time and both systems will have identical data. Data replication is typically done through the software’s capabilities. This generally provides a recovery time of a few seconds.
Active-Active (Load Balanced): In this method both the primary and secondary systems are active and processing requests in parallel. Data replication happens through software capabilities and would be bi-directional. This generally provides a recovery time that is instantaneous. - 13What does the word "persistency" mean with respect to load balancing?An important issue when operating a load-balanced service is how to handle information that must be kept across the multiple requests in a user's session. If this information is stored locally on one backend server, then subsequent requests going to different backend servers would not be able to find it.
Ideally the cluster of servers behind the load balancer should be session-aware, so that if a client connects to any backend server at any time the user experience is unaffected. Typically this information is stored in a client side cookie. - 14What are the advantages of RAID (eg. RAID10)?RAID is a form of data protection scheme by using multiple data drives to store data. It is designed with drive failure/faults in mind, allowing the integrity of the data to have the ability to remain intact by swapping out bad drives with new ones.
In most cases RAID 10 provides better throughput and latency than all other RAID levels except RAID 0 (which wins in throughput) but is bad for availability. Thus, it is the preferable RAID level for I/O-intensive applications such as database, email, and web servers, as well as for any other use requiring high disk performance - clusters.
RAID0 - stripes across all disks, shouldn't be used if data is important
RAID1 - mirror data on multiple disks
RAID5 - needs at least 3 disks, 2 for data 1 for parity
RAID6 - needs at least 4 disks, 2 for each data block and two for storing parity blocks
RAID10 combines fast RAID0 with secure Mirror. RAID 10 is a stripe of mirrors. - 15What happens (can happen) with dynamic routing if a link or device is "flapping" (on - off - on - off - on...)?Depends on the routing but it could affect the latency and jitter of the connection, also packet loss would be possible
A route flap occurs when a router alternately advertises a destination network via one route then another, or when there’s an interface error on the router that alternates the availability of the router as up or down. When this happens repeatedly, the routing topology is distorted and it becomes difficult for the traffic-sending network device to determine the next route hop. The longer it takes to determine the next possible route path, it’ll lead to the network service latency or downtime. Some level of route flap is unavoidable and is quite common. But when the flap frequency is very intensive and the destination router availability status keeps fluctuating, the routing topology would not converge and the traffic may be re-routed to other devices creating routing loops making the situation even worse. - 16What is the main disadvantage of a cold stand-by setup?Long recovery time which is not great for service availability
Depending on the amount of time that the device has been turned off, means that it will be potentially behind on software updates, and when turned on, would likely not be compatible with other devices, and could pose a security risk.
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- Informatik FlashCards sobre Hardware and Redundancy, criado por Simon Perez em 05-12-2019.
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- Simon Perez
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