Microsoft recommend that number of concurrent virtual machines deployed using the any particular snapshot or .vhd file is limited to 20.
If more than 20 virtual machines are required, an additional disk can be created for the additional virtual machines.
Procedure
In the Azure portal, select All Services.
In the All Services search box, enter disks and then select Disks to display the list of available disks.
Select the disk that you would like to use. The page for that disk appears.
From the menu at the top, select Create snapshot.
Enter a Name for the snapshot.
Choose a Resource group for the snapshot. You can use either an existing resource group or create a new one.
For Account type, choose Standard (HDD) or Premium (SSD) storage.
When done, select Create to create the snapshot.
After the snapshot has been created, select Create a resource in the left menu.
In the search box, enter managed disk and select Managed Disks from the list.
On the Managed Disks page, select Create.
Enter a Name for the disk.
Choose a Resource group for the disk. You can use either an existing resource group or create a new one. This selection will also be used as the resource group where you create the virtual machines from the disk.
For Account type, choose Standard (HDD) or Premium (SSD) storage.
In Source type, select Snapshot.
In the Source snapshot drop-down, select the snapshot created earlier.
Make any other adjustments as needed and then select Create to create the disk.
