In Microsoft Azure, What server size/series uses credits and slows down if the credits run out?

In Microsoft Azure, What server size/series uses credits and slows down if the credits run out?

• F series
• D series
• B series
• A series

EXPLANATION

 B-series 

These are known as “burstable” VMs.  They are very useful but the way they work is a bit complicated.  B-series are used for non-CPU intensive workloads (e.g. domain controllers, file servers) and cost about 50% of an equivalently sized Ds-series VM.  The reason they’re cheaper is because Azure imposes a quota on how much of the total CPU cores can be used.  This quota is usually a fraction of the total available CPU. 
For instance, B2m’s quota is 60% of a single CPU, which is 30% of the 2 CPUs visible in the VM.  Every second that the VM is using less than its quota (less than 60% of a single CPU) it is “banking credits”.  These banked credits can be used to burst up to the total available CPUs (100% of 2 CPUs, in this example) when needed.  While bursting, the VM is consuming its banked credits.  Once credits run out, the VM’s CPU utilization is throttled down to its 60% quota.
Why use B-series VMs?  They are cheaper.  For approximately the same price that you would pay for a Ds-series VM, you can get a B-series with double the CPUs and double the RAM.  However, they should only be used for workloads that are either not CPU intensive or “bursty”, meaning they only occasionally need all the CPU but most of the time the CPU is idle. 
For instance, an Active Directory domain controller is not utilizing its CPU very heavily on a regular basis.  However, when Windows Updates run, the VM will use all its available CPU horsepower.  B-series are perfect for Domain Controllers since they bank credits while idle and then consume them when needed to update or do some other CPU intensive task.

• Purpose: General, non-CPU intensive workloads (e.g. AD domain controllers, file servers) 
• CPU clock speed: varies 
• vCPU-to-RAM ratio: varies from 1:1 to 1:4 for VMs larger than B2s 
• Storage supported: Standard and Premium 
• Approximate average list price per CPU: ranges from $13/month to $40/month 

Nerdio Tips:

• Don’t use B-series VMs for CPU intensive workloads 
• When a B-series VM is first provisioned, it doesn’t have any banked credits and is subject to its quota limit on the CPU, which means it’s slow.  Once the VM is running idle for some time, credits get banked and the VM performance improves when it needs to burst. 
• Don’t shut down B-series VMs overnight when they are not in use.  This will not allow the VMs to bank credits for the following day of usage.

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On ARM64 processors, what exception level does the kernel run in?

On ARM64 processors, what exception level does the kernel run in?

• EL3
• EL2
• EL0
• EL1

EXPLANATION

Privilege and Exception levels

Before we explain the details of the Armv8-A exception model, let's start by introducing the concept of privilege. Modern software expects to be split into different modules, each with a different level of access to system and processor resources. An example of this is the split between the operating system kernel, which has a high level of access to system resources, and user applications, which have a more limited ability to configure the system.

Armv8-A enables this split by implementing different levels of privilege. The current level of privilege can only change when the processor takes or returns from an exception. Therefore, these privilege levels are referred to as Exception levels in the Armv8-A architecture. Each Exception level is numbered, and the higher levels of privilege have higher numbers.
As shown in the following diagram, the Exception levels are referred to as EL<x>, with x as a number between 0 and 3. For example, the lowest level of privilege is referred to as EL0.

A common usage model has application code running at EL0, with an operating system running at EL1. EL2 is used by a hypervisor, with EL3 being reserved by low-level firmware and security code.

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Which routing loop avoidance / prevention mechanism should be disabled on a multi-point interface?

Which routing loop avoidance / prevention mechanism should be disabled on a multi-point interface?

• spanning tree
• reverse path forwarding
• route poisoning
• split horizon 

EXPLANATION

A routing loop is a serious network problem which happens when a data packet is continually routed through the same routers over and over. The data packets continue to be routed within the network in an endless circle. A routing loop can have a catastrophic impact on a network, and in some cases, completely disabling the network. Normally Routing Loop is a problem associated with Distance Vector Protocols. How routing loops affect network performance? • A major portion of the precious bandwidth which is available for normal user traffic of the affected routers will be consumed by looping IP datagram packets. • The major portion of the processing power of the affected routers is used to process the looping IP datagram packets. Routing Loop can happen in large internetworks when a second topology change emerges before the network is able to converge on the first change. Convergence is the term used to describe the condition when all routers in an internetwork have agreed on a common topology. Link state protocols tend to converge very quickly, while distance vector protocols tend to converge slowly. The following methods are used to avoid Routing Loops. Maximum hop Count Maximum hop count mechanism can be used to prevent Routing Loops. Distance Vector protocols use the TTL (Time-to-Live) value in the IP datagram header to avoid Routing Loops. When an IP datagram move from router to router, a router keeps track of the hops in the TTL field in the IP datagram header. For each hop a packet goes through, the packet’s TTL field is decremented by one. If this value reaches 0, the packet is dropped by the router that decremented the value from 1 to 0. Split Horizon A split horizon is a routing configuration that stops a route from being advertised back in the direction from which it came. Split Horizon mechanism states that if a neighbouring router sends a route to a router, the receiving router will not propagate this route back to the advertising router on the same interface. Route Poisoning Route Poisoning is another method for avoiding routing loops. When a router detects that one of its connected routes has failed, the router will poison the route by assigning an infinite metric to it. Hold-down Timers Hold-down timer is another mechanism used to prevent bad routes from being restored and propagated by mistake. When a route is placed in a hold-down state, routers will neither advertise the route nor accept advertisements about it for a specific interval called the hold-down period.

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in the european eDelivery standard PEPPOL AS4, which protocol is used to retrieve the information about the location of participant capabilities?

in the european eDelivery standard PEPPOL AS4, which protocol is used to retrieve the information about the location of participant capabilities?

• isdn
• DNS
• https
• http 

EXPLANATION

This section includes specifications and resources to enable access to the PEPPOL eDelivery Network and to implement the following components: Access Points, gateways which ensure a standard and solid transport mechanism to exchange different types of documents across different communities or countries; Service Metadata Publishers (SMPs), which contain the exact location and the capabilities of participants; Service Metadata Locator (SML),
used to add/update/delete the IDs of the participants, and which offers a DNS-based mechanism to discover the SMP where the specific participant data is described.

 

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What does WAN stand for?

What does WAN stand for?

• Wide-Area Network
• Wireless Area Network
• Weekly Activity Notification
• World Association of Newspapers 

EXPLANATION

a computer network in which the computers connected may be far apart, generally having a radius of more than 1 km.

A wide area network is a telecommunications network that extends over a large geographical area for the primary purpose of computer networking. Wide area networks are often established with leased telecommunication circuits.

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