#Shadow virtual computer software#
#Shadow virtual computer windows#

Examples of applications providing a VSS writer are Microsoft SQL Server and Exchange Server.

Each application with VSS support adds its writer to the operating system during installation.

#Shadow virtual computer software#

The writers are software components that write data to files and databases to ensure consistency.

Hardware providers offload the host OS when creating a shadow copy. Hardware providers are usually used with SAN storage (storage area network).

#Shadow virtual computer windows#

The copy-on-write software VSS provider is included in the Windows OS. The VSS provider can have a software or hardware implementation.

The VSS provider is the core component of VSS, which creates shadow copies (snapshots) of volumes.

To understand how VSS works, we first need to go over the components that make up this feature. This technology allows creating point-in-time copies of files that are open and in use without compromising integrity and usability of these copies. Here, Volume Shadow Copy Service (VSS) can help. When you are using applications or databases like Microsoft SQL Server, Active Directory, or Exchange Server, you cannot just close the file and then append data to it. However, if the backup process starts at the moment when certain transactions are running, and I/O (input/output) operations are in place, data may be lost. This approach may work well for file systems with not a very high load, such as internal file storage or web servers. Once the backup process is completed, the delta file is merged with the. After the delta file is created, the backup software starts copying data from the read-only. To store the changes made during the backup process on the master disk, VMware ESXi creates a delta file connected to the main.

vmdk files in VMware environments) become read-only. During this process, all VM disks (which are represented as. When the backup process starts, a snapshot, that is, an exact copy of the VM, is taken. One way to avoid this situation is snapshot-based VM backup. What you get is data blocks that are not consistent and do not represent a single specific point in time. By the time the other parts of the file are copied to the backup repository, the blocks in the first part have changed. While the first part of the file is being copied, blocks used by other parts of the file are changing. This application is continuously changing data in the opened file by writing/deleting blocks. Suppose that a file is continuously used by an application such as a database or a system application. Such a backup is created by just copying each block in the state that it is in at the time of being copied. Without VSS, you get an inconsistent backup.

Consistency guarantees that the applications running on virtual or physical machines are fully functional after they are restored from a backup. Why You Need the VSS TechnologyĪpplication data consistency is important for VM and physical server backups. VSS was first released with Windows XP and Windows Server 2003. Volume Shadow Copy, also referred to as Volume Snapshot Service, is a set of COM (Component Object Model) interfaces in Windows, which provide the framework to create consistent backups for different applications. A volume snapshot, also called a shadow copy, is created in the Windows operating system.Buffers from memory are written to disk, that is, flushed and the file system is frozen.VSS temporarily stops writing operations performed by applications.To achieve backup data consistency, the following happens: Volume Shadow copy Service (VSS), a native feature of Windows operating systems, facilitates the creation of consistent application-aware backups. This blog post explains what Volume Shadow Copy Service (VSS) is, how it works, and why this technology is important for backing up Windows-based virtual and physical machines. For this purpose, Microsoft developed the VSS technology. Having consistent backup data facilitates recoveries without data corruption or delays. When creating a backup of a virtual or physical machine with running applications, especially applications that intensively write data to files and databases, ensuring backup data consistency is essential.