Ephemeral OS Disks
Warning: Nerdio Manager does not install the BgInfo Azure extension during any automation or management process. However, the BgInfo extension may be installed either through a scripted action directly, or unintentionally, as stated in the Azure PowerShell module issues report.
Ephemeral OS disks are a type of disk storage that have no associated storage costs. In addition, they are generally faster than traditional managed disks because they run inside the SSD disk cache on a physical host where each session host VM resides.
This is very useful when employed in conjunction with Nerdio Manager's auto-scale feature where you can create and destroy session host VMs using the lowest cost (free) and fastest type of storage.
Note: Session host VMs that use an Ephemeral OS disk cannot be stopped and deallocated. That is, put in a state where you are not paying for the session host VM's compute capacity. A session host VM that is stopped and deallocated releases its disk cache storage. Since this is where the Ephemeral OS disk is stored, it can no longer be powered on because its data has been deleted. Therefore, any session host VM that uses Ephemeral OS disk must be destroyed to free its compute capacity.
To configure a host pool using Ephemeral OS disks:
Navigate to the desired Workspace > Dynamic host pools.
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Select Add dynamic host pool.
Note: See Create Dynamic Host Pools for full details.
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Enter the following information:
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Desktop Image: From the drop-down list, select the desktop image that is used as the golden image for newly created session hosts.
Note: The size of the selected desktop image is important with regards to the configuration of the Ephemeral OS disk. Different VM Sizes have different amounts of disk cache allocated to them. In fact, some have no disk cache at all. In addition, a VM Size that does not support Premium SSD, will not support Ephemeral OS disk.
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VM Size: From the drop-down list, select a disk that has disk cache and supports Premium SSD.
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OS Disk: From the drop-down list, select the desired Ephemeral OS disk.
Note: If the VM Size selected does not have enough disk cache to fit the desktop image, then the Ephemeral OS disk is grayed out and cannot be selected. That is, you can only use Ephemeral OS disk with certain families and only with VM Sizes that are large enough.
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Once you have entered all the desired information, select OK.
The host pool is created.
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In Auto-scale configuration, in the Host Pool Sizing section, enter the following:
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Base host pool capacity: This is grayed out, which means you cannot set a custom value.
Note: The Base host pool capacity is always set to the Min active host capacity. This is because a session host VM that has an Ephemeral OS disk cannot be stopped and deallocated. In addition, it must be destroyed to free up that capacity.
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Min Active Host Capacity: Type the minimum number of running session hosts that are always available.
Tip: For example, you can set the Min Active Host Capacity to 0 and the Burst Beyond Base Capacity to 10. This means there are no session host VMs remaining when they are scaled in. Therefore, you have no compute costs and no storage costs.
Burst Beyond Base Capacity: Type the capacity to burst above the standard number of session host VMs when there is user demand. The system automatically creates up to this number of new session host VMs above the Base Host Pool Capacity, when needed. These session hosts are the first ones to be removed when the system scales in after business hours.
Note: In the Estimated Monthly Costs box, you will note that the storage costs are 0 because you are using Ephemeral OS disks.
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