All Microsoft Azure Linux instances get a /mnt/resource /dev/sdb1 location. This location isn’t some “Microsoft Screwup” or a free data drive where you can store all the information you want. Rather it’s a high iop low latency space which was intended to be used for a swap or temporary storage. However, its’ a great use for anything tmpfs like /tmp /var/tmp etc or your all of your swap location.
This temporary drive is not represented in your storage blob therefore you’re not charged for the utilization or usage of it. The temporary drive should be considered volatile and everything in it will be lost at any time the system is shutdown, reset, powered off either accidentally, due to service self-healing, on purpose etc.
Again, this location should ONLY be used as temp space for anything that does not need to be saved. The data lost on the drive will not be recovered if lost.
Want to learn more? Read Virtual Machines Disks VHDs by Mircosoft.