What is Latency?

What is Latency? KB ID 0001874

What is Latency?

I hear people use the word ‘Latency‘ a lot, mostly without ever really understanding what it is, unlike its close relations bandwidth and thoughput* which are measurments of data, latency is a measurment of TIME, and in a lot scenarios is variable depending on what’s happening.

*Note: Too low bandwidth and thoughput can increase latency.

There will always be latency, becasue we are bound by the laws of physics, to pass a ‘light pulse’ down a fibre optic cable from London to Paris, will take less time than it will to pass that same lightpulse from London to New York. We call this propogation delay.

  1. Propagation Delay: This is the time it takes for a signal to travel from the sender to the receiver through the physical medium (such as fiber optics or copper cables). The speed of propagation is close to the speed of light but can vary slightly depending on the medium.
  2. Transmission Delay: This is the time required to push all the packet’s bits onto the wire. It is influenced by the size of the packet and the transmission rate of the network.
  3. Processing Delay: This is the time taken by network devices like routers and switches to process the packet header and make forwarding decisions. Processing delays are generally very small but can add up across multiple devices.
  4. Queuing Delay: This occurs when a packet waits in a queue before it can be transmitted. Queuing delays can vary significantly depending on the network congestion and the configuration of the network devices.
  5. Propagation Distance: The physical distance between the source and destination plays a critical role in latency. Longer distances naturally result in higher latency due to the increased time it takes for signals to travel.
  6. Network Congestion: High traffic volumes can cause congestion in the network, leading to increased queuing delays and, consequently, higher overall latency.
  7. Bandwidth and Throughput: Although bandwidth is the maximum rate of data transfer, actual throughput can be lower due to various factors, including network congestion and overheads. Lower throughput can contribute to higher latency.
  8. Protocol Overheads: Different network protocols have various overheads associated with them. For instance, the Transmission Control Protocol (TCP) has higher overhead due to its error-checking and recovery features compared to the User Datagram Protocol (UDP).
  9. Hardware and Software Limitations: The performance of network hardware (like routers, switches, and network interface cards) and software (such as drivers and network stacks) can impact latency. Faster and more efficient hardware and software reduce latency.

Latency is typically measured in milliseconds (ms) and can be assessed using various tools and techniques, such as ping tests and traceroute commands. Lower latency is especially crucial for applications requiring real-time interaction, such as online gaming, video conferencing, and financial trading systems.

Minimizing network latency involves optimizing network infrastructure, improving hardware and software efficiency, and ensuring adequate bandwidth and throughput to handle the expected traffic load.

What is Latency and Why is this Important?

Well the complaint is nearly always “We are experiencing latency issues“, usually when the ‘users’ are having performance issues with ‘something’. Now sometimes the problem IS the network (shock & horror). But all the bandwidth/Thoughput and Low latency in the worlds will not help you if you have a poorley coded application, or your DNS is not seup correctly.

But it’s not just old and poorley coded applications that require low latency Some application platforms we take for granted can suffer for example.

  1. Online Gaming: Real-time multiplayer online games require low latency to ensure smooth gameplay and quick reactions. High latency can result in lag, making the gaming experience frustrating and uncompetitive.
  2. Video Conferencing: Applications like Zoom, Microsoft Teams, and Skype require low latency to facilitate real-time communication. High latency can cause delays, leading to awkward conversations and reduced communication quality.
  3. Voice over IP (VoIP): Services like Skype, WhatsApp, and other internet-based telephony services need low latency to provide clear and immediate voice communication. High latency can cause echo and delays, making conversations difficult.
  4. Financial Trading: Stock trading platforms and high-frequency trading systems rely on low latency to execute trades in milliseconds. Even minor delays can result in significant financial losses or missed trading opportunities.
  5. Telemedicine: Remote medical consultations, surgeries, and other healthcare services often require low latency to ensure accurate diagnostics and timely intervention.
  6. Augmented Reality (AR) and Virtual Reality (VR): AR and VR applications need low latency to provide immersive and responsive experiences. High latency can cause motion sickness and degrade the user experience.
  7. Industrial Automation and Control Systems: Manufacturing processes, robotics, and other industrial applications require low latency for precise control and real-time monitoring to ensure safety and efficiency.
  8. Autonomous Vehicles: Self-driving cars and drones rely on low latency for real-time data processing and decision-making to navigate safely and respond to dynamic environments.
  9. Cloud Gaming: Services like Google Stadia, NVIDIA GeForce Now, and Xbox Cloud Gaming stream games from the cloud to users’ devices. Low latency is critical to provide a responsive gaming experience comparable to playing on a local console or PC.
  10. Smart Grids: Advanced electrical grid systems require low latency for real-time monitoring and control to manage power distribution efficiently and respond to fluctuations in demand and supply.
  11. Remote Desktop Applications: Tools like Remote Desktop Protocol (RDP) and Virtual Network Computing (VNC) require low latency to provide a seamless and responsive experience when accessing and controlling a remote computer.
  12. Live Streaming: Interactive live streaming platforms like Twitch and YouTube Live require low latency to ensure minimal delay between the broadcaster and viewers, enabling real-time interaction through chat and other features.

Ensuring low latency for these applications often involves optimizing network infrastructure, using efficient communication protocols, and sometimes deploying edge computing to process data closer to the source.

Related Articles, References, Credits, or External Links

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Resizing Windows Volumes / Drives in VMware vSphere / ESX

KB ID 0000381 

Problem

This article is primarily geared towards making your guest virtual machines hard drives LARGER, If you want to SHRINK or make the drive smaller then see the following article.

Resizing Guest Hard Drives using the VMware Converter

Solution

Re sizing a Guests Hard Drive (Make it larger)

1. On the properties of the VM select the hard disk in question and locate its size.

2. Enter the new size and hit OK. Note: Making the drive size smaller, will have no affect, if you want to do that clone the drive. If the option is “Greyed out” then make sure you DO NOT have any snapshots for this machine.

Re-sizing the guests “Volume” Option 1 – Graphically

Note: To do this using diskpart skip forward to number 10.

3. On the guest > Right click “My Computer” > Manage > Locate “Disk Management”. You will see there’s some free space that’s appeared on the end of the drive, (Click action > Re-scan if you can’t see it).

4. Simply right click the existing volume and select “Extend Volume”.

5. Next.

6. Copy in the extra space you want to assign (all of it probably) > Next.

7. Finish.

8. All the physical drive should now be committed.

9. And just to be sure, look in “My Computer” the drive is now 300 GB.

Re-sizing the guests “Volume” Option 2 – From Command Line with diskpart

10. Start > run > cmd{enter}

[box]diskpart list volume&lt select volume x –Where x is the volume number of the volume to be re sized[/box]

11. The final command is simply extend (This uses ALL the available free space.) Note the volume size in the picture below has jumped up by 40 GB.

Resizing a System (boot) Partition.

Server 2008 R2 and Windows 7 can do this quite happily. Older versions of Windows do not like having their system drive re sized, you see the following error if you try,

Error: The volume you have selected may not be extended. Please select another volume and try again.

Option 1 (Connect this drive to another machine)

In a virtual environment this is much simpler, but even if its a real physical hard drive, you can put it into another server and re size it. In an ESX environment simply do the following,

1. Shut down the machine that needs its drive re sizing, then go to another virtual machine’s properties and select add.

2. Hard Disk > Next.

3. Select “Use existing virtual disk” > Next.

4. Browse to the the drive we want to re size > Next.

5. Next.

6. Finish.

7. Now on the VM (Action > Re-scan disks). You will see the drive, and it’s not listed as a system drive, so you can extend it using any of the methods listed above.

8. For example, heres the drive re sized using disport.

9. when you have re sized the drive go back to the properties of the machine you have connected it to, and remove it.

10. OK.

11. Now power on the original VM and drive will be re sized.

Option 2 (Re size the Windows volume with GParted)

Note: This will work for a physical server as well.

1. Here’s our system drive with some nice shiny free space.

 

2. Make sure the server in question can boot from CD, in VMware do the following to boot to the machines BIOS, for a real server watch the screen as the server boots for instructions (Usually F10, F1 or Esc but differs depending on vendor).

3. Locate the boot order and make sure CD/DVD is at the top of the list.

4. Download GParted burn the image to CD, if you are working on a real server (use ImgBurn if your stuck). Or simply point the VM to the iso image, and boot the machine in question from it. At the welcome screen press Enter.

5. Use your arrow and tab keys to select Don’t touch the keymap > OK.

6. Pick a language.

7. We want to launch the GUI (X Windows), so select 0 (Zero).

8. Select Re size/Move > Drag the arrow to include the free space > Re size/Move.

9. Apply

10. Apply.

11. Close.

12. Click GParted > Quit.

13. Exit > Reboot/Shutdown > OK.

14. Remove the CD/ISO and press Enter.

15. The guest will run chkdsk the firs time it boots. This is normal don’t panic.

16. Once booted the volume will be re sized.

Shrink a Windows Partition with diskpart

1. To actually make the volume smaller with diskpart, the initial commands are the same.

2. If you use “shrink” on its own is will shrink the drive as much as it can (I cannot think of any situation where you would do this!). So to shrink the volume by 10 GB simply issue a “shrink minimum 10240”. (The figure in in MB).

 

Related Articles, References, Credits, or External Links

Original Article Written 24/01/11

Dell PowerEdge – PERC RAID Card Importing / Using ‘Foreign’ Disks

KB ID 0000639 

Problem

I bought some SAS disks from eBay to go in my Power Edge 2900 Server, and scratched my head for a while trying to get the PERC RAID controller to use them. I could only see them marked as ‘Foreign’. Probably because they did not have their original config ‘wiped’ off them before I bought them.

Solution

1. Boot the server, Press CTRL+R when prompted, then press ‘C’ to enter the Configuration Utility.

WARNING: DONT clear the config on the controller or you lose ALL your Virtual Disks / Arrays.

2. Select the controller > F2 > Foreign Config > Clear > Confirm.

3. You can now add the disk(s) as a new Virtual Disk.

4. I’m just presenting one 300GB SAS disk as RAID0 here.

Related Articles, References, Credits, or External Links

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