Aure Backup Snapshot Consistency Details

Apurva Pathak 590 Reputation points
2024-08-14T09:11:58.4+00:00

Hi folks,

May I please request you all to help me understand the different Azure Backup consistency types in detail.

Any help is highly appreciated!

Cheers!
Apurva

Azure Backup
Azure Backup
An Azure backup service that provides built-in management at scale.
1,280 questions
Windows Server Backup
Windows Server Backup
Windows Server: A family of Microsoft server operating systems that support enterprise-level management, data storage, applications, and communications.Backup: A duplicate copy of a program, a disk, or data, made either for archiving purposes or for safeguarding valuable files from loss should the active copy be damaged or destroyed.
476 questions
0 comments
Accepted answer
  1. SadiqhAhmed-MSFT 46,036 Reputation points Microsoft Employee
    2024-08-22T21:23:32.01+00:00

    @Apurva Pathak When you perform a backup of an Azure VM, there are two types of backups that can be performed: application-consistent backups and file system-consistent backups.

    Application-consistent backups use the Volume Shadow Copy Service (VSS) to ensure that all data in memory and on disk is in a consistent state at the time of the backup. This is important for applications that have databases or other data that is constantly changing.

    File system-consistent backups, on the other hand, do not use VSS and only ensure that the file system is in a consistent state at the time of the backup. This type of backup is typically used for file servers or other systems that do not have databases or other applications that require application-consistent backups.

    If the response helped, do "Accept Answer" and up-vote it

    0 comments

1 additional answer

Sort by: Most helpful
Most helpful Newest Oldest
  1. Marcin Policht 25,290 Reputation points MVP
    2024-08-14T09:16:29.87+00:00

    Refer to https://video2.skills-academy.com/en-us/azure/backup/backup-azure-vms-introduction#snapshot-consistency

    Snapshot Details Recovery Consideration
    Application-consistent This is the default setting in the VM backup policy. App-consistent backups capture memory content and pending I/O operations. App-consistent snapshots use a VSS writer (or pre/post scripts for Linux) to ensure the consistency of the app data before a backup occurs. When you're recovering a VM with an app-consistent snapshot, the VM boots up. There's no data corruption or loss. The apps start in a consistent state. Windows: All VSS writers succeeded

    Linux: Pre/post scripts are configured and succeeded| |Application-consistent|This is the default setting in the VM backup policy. App-consistent backups capture memory content and pending I/O operations. App-consistent snapshots use a VSS writer (or pre/post scripts for Linux) to ensure the consistency of the app data before a backup occurs.|When you're recovering a VM with an app-consistent snapshot, the VM boots up. There's no data corruption or loss. The apps start in a consistent state.|Windows: All VSS writers succeeded Linux: Pre/post scripts are configured and succeeded| |File-system consistent|This is the default setting in the VM backup policy. File-system consistent backups provide consistency by taking a snapshot of all files at the same time.|When you're recovering a VM with a file-system consistent snapshot, the VM boots up. There's no data corruption or loss. Apps need to implement their own "fix-up" mechanism to make sure that restored data is consistent.|Windows: Some VSS writers failed Linux: Default (if pre/post scripts aren't configured or failed)| |Crash-consistent|Crash-consistent snapshot is an opt-in setting in the VM backup policy. Azure Backup also takes crash-consistent backups if the VM is not running during backup and when application/file-consistent backups fail. Only the data that already exists on the disk at the time of the backup operation is captured and backed up; data in read/write host cache isn't captured.|Starts with the VM boot process followed by a disk check to fix corruption errors. Any in-memory data or write operations that weren't transferred to disk before the crash are lost. Apps implement their own data verification. For example, a database app can use its transaction log for verification. If the transaction log has entries that aren't in the database, the database software rolls transactions back until the data is consistent.|When you have opted for application/file-system backup and VM is in shutdown (stopped/ deallocated) state and when the snapshot is retried. You have opted for agentless crash consistent backups|

    If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

    hth

    Marcin

Your answer

Answers can be marked as Accepted Answers by the question author, which helps users to know the answer solved the author's problem.