[gxti]

> How does one revert this without physical access to the drive?

I know this was a rhetorical question, but I'll answer anyway: It isn't possible. Not only is there no way to read latent data normally from a drive that has been zeroed (drives that fail this test are called "defective"), but it is currently understood that recovering data from a modern drive that has been overwritten with a single pass of random data is impossible at any expense.

http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html#E...

However, data can still leak out of cloud stores in the same way that it leaks out of solid-state disks and even magnetic disks: there's no guarantee that a given logical block will always be mapped to the same underlying hardware. A mirrored drive may be fail and thrown in the trash with data still on it, or written blocks might be mapped to different places in an array for any number of reasons. This shouldn't result in leakage to other customers although it is up to the vendor to make sure this doesn't happen.

Depending on the implementation, vendor-supplied encryption may or may not mitigate this risk, but customer-supplied encryption always will because the customer knows where the dividing line stands.

[cloudsigma]

That's great information and you are right. Secure disposal of drives by the vendor is of course also extremely important.

For those deleting virtual drives in the cloud securely the points made in the post might seem obvious but I believe most users in the cloud don't undertake such measures. That's why the encryption option is another way to go and implicit so much more likely to be taken up by cloud users.

Customer side encryption is great and of course usually means access is restricted to the customer, the issue is server restarts, crashes etc. which require manual intervention to get the file system or data directories back up and running again. In a dynamic cloud environment this can be particularly cumbersome.

Best wishes,

Patrick