File Highwater Marking

One possible threat to system security is disk scavenging. Disk scavenging is the attempt to read contents of deleted files remaining on disk after deletion. As a performance benefit, files are not actually erased from disk by default, but only the pointers to them are removed. The file contents are not actually destroyed until the next file to occupy the same disk blocks overwrites the storage space. One way to perform disk scavenging is to allocate some amount of disk space to a new file, but to write no data to the file. The new owner of that space can then potentially examine the old contents.

The OpenVMS file system supports highwater marking, a mechanism that ensures that a file owner cannot read blocks he has not written himself, but it causes a slight performance degradation. Your system manager can enable this feature at his discretion.