Azure file access failure (ERROR 1/Invalid MS-DOS function) from a VHD mounted from the blob

Question

After scaling to 500 VMs, some of them (about 20 last time I tried) fail to start properly because their startup script cannot read a file from the mounted VHD. The VHD is mounted from the blob, and then the startup script copies some files from it.

The logs show the following output when trying to copy the file:

2013/06/26 12:39:55 ERROR 1 (0x00000001) Copying File F:\Folder\file.xxx Incorrect function.

When I try copy it manually in Windows Explorer, I get an error message with the following contents: Invalid MS-DOS function. (Try Again/Cancel)

The drive is visible in Windows Explorer, and you can navigate in the folders (though, I think, not all)

Any ideas what can be causing it?

Some additional details: The VHD is mounted read-only from the blob by creating a snapshot for each of the machines. On most of the VMs, there are no problems accessing the files, but when you scale out, some of them fail to complete the operation. Geo-replication is enabled.

Answer 1

Issues found: when scaling out, there was another vaguely-related bottleneck which slowed down the startup so much that the SAS expired, so we lost access to the drive. I'll have to re-think the way the files are accessed so that we do not have such slowdowns (this issue must be addressed anyway)