I created a PowerShell cloud shell in Azure portal, configured to use an existing general purpose v2 storage account. Created a new file share and gave it a name. When I look inside the file share, I can see a folder ".cloudconsole" with one file inside "acc_[name].img". The size of the file is 5GB.
Question:
The cloud shell needs Azure File Share to act as clouddrive that store file. So it will ask you create storage account when you use cloud shell.
And the ".img" file is an image of a computer that it works for the cloud shell, and it's free. It just costs for the storage account. You can get more details here.
The previous answer does have the link to what the .img file is, standard Storage Account rates do apply. The Azure Pricing Calculator can give you the current pricing, but at the time I'm writing this, 5GB of Hot storage is about $0.10/mo plus read/write costs depending on how often you run it.
