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Fault domains and Update domains in Availability Set RRS feed

  • Question

  • Hi,

    While creating Availability Set, I have seen Fault domains and Update domains.

    Both are in numeric value.

    Please let me know why both are required and what does its number represent?

    Regards

    InTechSys


    InTechSys

    Thursday, May 23, 2019 9:35 PM

Answers

  • Hello,

    Thanks for posting your query here.

    Fault Domain ensures the availability of VM's by spreading them across multiple Faults domains (the number we provide in the screenshot mentioned by you) in case of physical Hardware failures.

    In Update Domain the VM's are considered as logical unit and are distributed based on the number provided. Incase if the VM's are to be rebooted for an application update or patch roll-out for security vulnerability these are done in sets to avoid application downtime. Each reboot is done for one set of VM's under one Update Domain and once they are back UP the other set goes for a reboot.

    Please find more details in the document.

    Requesting you to mark the reply as answer if it solved your issue or vote as helpful if it helped so that other community members can benefit from it.

    Thanks.

    Friday, May 24, 2019 4:49 AM
    Moderator
  • Hello,

    You can mention the values of Fault & Update Domains while creating the Availability Set. Once you create, you cannot modify these values.

    However there few things on Availability sets that you can update using Powershell and Azure CLI.

    A VM can only be added to an availability set when it is created. To change the availability set, you need to delete and then recreate the VM in a new Availability set. Please refer the document for steps.

    Do click on "Mark as Answer" and “Vote as Helpful” on the post that helps you, this can be beneficial to other community members.

    Thanks.

    Monday, May 27, 2019 12:00 PM
    Moderator

All replies

  • Hello,

    Thanks for posting your query here.

    Fault Domain ensures the availability of VM's by spreading them across multiple Faults domains (the number we provide in the screenshot mentioned by you) in case of physical Hardware failures.

    In Update Domain the VM's are considered as logical unit and are distributed based on the number provided. Incase if the VM's are to be rebooted for an application update or patch roll-out for security vulnerability these are done in sets to avoid application downtime. Each reboot is done for one set of VM's under one Update Domain and once they are back UP the other set goes for a reboot.

    Please find more details in the document.

    Requesting you to mark the reply as answer if it solved your issue or vote as helpful if it helped so that other community members can benefit from it.

    Thanks.

    Friday, May 24, 2019 4:49 AM
    Moderator
  • If I change the value of Fault domains and Update domains, what will be the effect in VM or resources?

    InTechSys

    Saturday, May 25, 2019 9:10 AM
  • Hello,

    You can mention the values of Fault & Update Domains while creating the Availability Set. Once you create, you cannot modify these values.

    However there few things on Availability sets that you can update using Powershell and Azure CLI.

    A VM can only be added to an availability set when it is created. To change the availability set, you need to delete and then recreate the VM in a new Availability set. Please refer the document for steps.

    Do click on "Mark as Answer" and “Vote as Helpful” on the post that helps you, this can be beneficial to other community members.

    Thanks.

    Monday, May 27, 2019 12:00 PM
    Moderator