1. Prepared by Jaroslav makovski
Data backup
Prepared by Jaroslav makovski

2. Table of contents Windows Server Backup Volume Shadow Copy Service
Tape/Disk Backup

3. Windows Server Backup
The Windows Server Backup feature automatically backs up and restores application data.
Windows Server Backup also provides registry keys and APIs that:
Allow your application to appear in the Recovery Wizard as a separately recoverable item.
Allow your cloud backup provider to report its status in the Windows Server Backup Microsoft Management Console (MMC) snap-in.

5. Volume Shadow Copy Service
The Volume Shadow Copy Service (VSS) is a set of COM interfaces that implements a framework to allow volume backups to be performed while applications on a system continue to write to the volumes.

6. Volume Shadow Copy Service
Backing up and restoring critical business data can be very complex due to the following issues:
The data usually needs to be backed up while the applications that produce the data are still running. This means that some of the data files might be open or they might be in an inconsistent state.
If the data set is large, it can be difficult to back up all of it at one time.

7. Volume Shadow Copy Service
VSS coordinates the actions that are required to create a consistent shadow copy (also known as a snapshot or a point-in- time copy) of the data that is to be backed up. The shadow copy can be used as-is, or it can be used in scenarios such as the following:
You want to back up application data and system state information, including archiving data to another hard disk drive, to tape, or to other removable media.
You are performing disk-to-disk backups.

8. How VSS Works
A complete VSS solution requires all of the following basic parts:
VSS service - Part of the Windows operating system that ensures the other components can communicate with each other properly and work together.
VSS requester - The software that requests the actual creation of shadow copies, Typically, this is the backup application.
VSS writer - The component that guarantees we have a consistent data set to back up. This is typically provided as part of a line-of-business application, such as SQL Server® or Exchange Server.
VSS provider - The component that creates and maintains the shadow copies. This can occur in the software or in the hardware.

9. How a Shadow Copy Is Created
The requester asks the Volume Shadow Copy Service to enumerate the writers, gather the writer metadata, and prepare for shadow copy creation.
Each writer creates an XML description of the components and data stores that need to be backed up and provides it to the Volume Shadow Copy Service. The writer also defines a restore method, which is used for all components. The Volume Shadow Copy Service provides the writer's description to the requester, which selects the components that will be backed up.

10. How a Shadow Copy Is Created
The Volume Shadow Copy Service notifies all the writers to prepare their data for making a shadow copy.
Each writer prepares the data as appropriate, such as completing all open transactions, rolling transaction logs, and flushing caches. When the data is ready to be shadow-copied, the writer notifies the Volume Shadow Copy Service.

11. How a Shadow Copy Is Created
The Volume Shadow Copy Service tells the writers to temporarily freeze application write I/O requests (read I/O requests are still possible) for the few seconds that are required to create the shadow copy of the volume or volumes. The application freeze is not allowed to take longer than 60 seconds. The Volume Shadow Copy Service flushes the file system buffers and then freezes the file system, which ensures that the file system metadata is recorded correctly and the data to be shadow-copied is written in a consistent order.

12. How a Shadow Copy Is Created
The Volume Shadow Copy Service tells the provider to create the shadow copy. The shadow copy creation period lasts no more than 10 seconds, during which all write I/O requests to the file system remain frozen.
The Volume Shadow Copy Service releases file system write I/O requests.
VSS tells the writers to thaw application write I/O requests. At this point applications are free to resume writing data to the disk that is being shadow-copied.

13. How a Shadow Copy Is Created
The requester can retry the process (go back to step 1) or notify the administrator to retry at a later time.
If the shadow copy is successfully created, the Volume Shadow Copy Service returns the location information for the shadow copy to the requester. In some cases, the shadow copy can be temporarily made available as a read-write volume so that VSS and one or more applications can alter the contents of the shadow copy before the shadow copy is finished. After VSS and the applications make their alterations, the shadow copy is made read-only. 

14. Complete copy
A complete copy is usually created by making a "split mirror" as follows:
The original volume and the shadow copy volume are a mirrored volume set.
The shadow copy volume is separated from the original volume. This breaks the mirror connection.
After the mirror connection is broken, the original volume and the shadow copy volume are independent. The original volume continues to accept all changes (write I/O requests), while the shadow copy volume remains an exact read-only copy of the original data at the time of the break.

15. Tape/Disk Backup
A strong disaster recovery strategy provides essential protection for your business, but to keep your data safe, you need to choose appropriate storage media. 

16. Disk backup
Disk backups provide some obvious advantages over tapes. Tape drives cannot randomly access data, so they offer extremely slow access speeds for individual files when compared to disk-based systems. Some manufacturers have attempted to correct this discrepancy by introducing specialized file systems that allow for faster access (notably IBM's Linear Tape File System), but tapes are still intrinsically slower than disk-based media in this respect.

17. Disk advantages Fast Access to Stored Data Lower Setup Costs
Easier to Recall Specific Backups Electronically
Flexible Security Features
Easier to Verify Written Data
Better Scalability

18. Tape backup
While tape backups require a significant initial investment, they often provide a better long-term return on investment for larger businesses. Tape drives use less electricity than disk-based systems, and you can store tapes for decades without losing data. However, media storage and management adds to the cost of a tape-based backup system.

19. Tape advantages Dependable Durability for Long-Term Storage
Greater Portability
Lower Costs for Enterprise-Level Systems
Excellent Security and Encryption Capabilities
Less Susceptible to Environmental Damage and Shock Damage
Effective for Full System Backups

20. Sources https://docs.microsoft.com/en-us/windows/desktop/backup
vs-disk-backup