Volume Shadow Copy (VSS): The Mechanism and the Practice — Why Backup Software Can Copy Files That Are Still in Use (archived 2026-08-30)

Abstract

Files that are in use can't normally be copied because of sharing violations — so how does backup software manage it? This article explains the roles of the Volume Shadow Copy Service (VSS) requester, writer, and provider, how copy-on-write works, day-to-day vssadmin operations, and the pitfalls of the diff area. Archived version of https://comcomponent.com/en/blog/vss-volume-shadow-copy-guide/, as published on 2026-08-30. The live article is maintained and may change after this date. First published 2026-08-01.