How does Azure delete the data when an Azure Disk attached to a VM is deleted

Question

Hello All:

I am working with one of my customers and their ask is "If I delete an Azure disk that has been attached to a VM and contains sensitive/proprietary data, how is that data protected, wiped, or guaranteed to be inaccessible to third parties?"

I did go through this document related to data center security for DBD(data bearing devices) destruction : https://learn.microsoft.com/en-us/compliance/assurance/assurance-data-bearing-device-destruction#data-destruction-overview. The document highlights the data sanitization categories but it does not come out clearly which category of sanitization is applied when an Azure disk is deleted.

Can you throw some light here? or atleast point me to right set of document resources?

Thanks,
--Mayur
Azure Professional Direct

Answer 1

Does a deleted disk is considered as a retired DBD? If so, that answers the question

no, it doesn't considered a retired DBD. Azure disks are virtual disks (literally, files) which may span one or multiple hardware disks. These disks may or may not be shared with other customers' data. When virtual disk is deleted, the physical disk is not necessary disposed, so your use case doesn't fall to retired DBD destruction policy. I think, this article gives a bit more hints: https://learn.microsoft.com/en-us/compliance/assurance/assurance-data-bearing-device-destruction, specifically:

Microsoft uses three categories of data sanitization for DBDs and assets containing data:
Clear: relates to the logical techniques that help to sanitize data in all user-addressable storage locations for protection against simple non-invasive data recovery techniques. These are techniques typically applied through the standard read and write commands to the storage device, such as by rewriting with a new value or using a menu option to reset the device to the factory state (where rewriting is not supported).

I think, this is your use case. This means that once you delete the VM disk is deleted, a "Clear" process is executed to wipe the data space previously allocated to your VM disk only. Then, cleared space can be allocated to very different customer. The link to NIST document (see response from @Bhanu Ejjagiri ) describe "Clear" process in a bit more details.

Physical disc destruction/retirement is a separate process which relies on hardware metrics such as read/write cycles, MTTF (mean time to failure) and/or other internal policies which are not related to VM disk delete processes.

Answer 2

Hi @Mayur Puli (Sonata Software North America)
Greetings for the day.

Each Microsoft datacenter uses an on-site process to sanitize and dispose of failed and retired DBDs. During this process, Microsoft personnel ensure chain of custody is maintained throughout the disposal process. And it is destroyed onsite using an approved standard operating procedure that meets NIST SP-800-88 guidelines. These DBDs are physically and logically tracked to maintain chain of custody through final disposition.

Reference # https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-88r1.pdf

Answer 3

Thank you Bhanu for your response. My main question is on the data stored in the Azure Disk (attached to a VM), the 1s and 0s. How is the data deleted and what standard Microsoft follows here.

The document here : protection-customer-data , says that Microsoft follows strict standards for overwriting storage resources before their reuse, as well as the physical destruction of decommissioned hardware. Other than that not much of information is available.

Does a deleted disk is considered as a retired DBD? If so, that answers the question

Regards,
--Mayur

Answer 4

Hi @Mayur Puli (Sonata Software North America)

When you delete a virtual machine (VM) in Azure, by default, any disks that are attached to the VM aren't deleted. This feature helps to prevent data loss due to the unintentional deletion of VMs.

So when you need to delete the data from the data disk ensure that the lease status is “unlocked” and that the lease state is “Available.” This indicates that the disk is not attached to any VMs and this will automatically delete the data .

Microsoft does not inspect, approve, or monitor applications that customers deploy to Azure. Moreover, Microsoft does not know what kind of data customers choose to store in Azure. Microsoft does not claim data ownership over the customer information that's entered into Azure.

You can see these policies form here

https://learn.microsoft.com/en-us/azure/security/fundamentals/protection-customer-data

https://learn.microsoft.com/en-us/compliance/assurance/assurance-data-retention-deletion-and-destruction-overview

----------

--If the reply is helpful, please Upvote and Accept it as an answer--