snapshots, VMware Tools, VSS and application consistency

[vmb01]

I'm trying to understand if a snapshots of a windows 2008 R2 VM that's running inside an ESXi 5.1 with  just a scsi disk is application consistent or not.

Reading here it seems yes, it's app consistent but there's a couple of things that I do not understand.

What does it mean: Restore must be done using the backup application’s guest agent. https://communities.vmware.com/The vSphere APIs for Data Protection provide no host agent support for this.

If I restore the entire VM, is this consistent or not?

[vNEX]

Hi,

What does it mean: Restore must be done using the backup application’s guest agent. https://communities.vmware.com/The vSphere APIs for Data Protection provide no host agent support for this.

lets say with VDP Advanced for consistent app backup and restore (which depends on VSS) like Exchange/SQL... you must have client agent installed in addition to vSphere APIs for Data Protection.

http://pubs.vmware.com/vsphere-55/topic/com.vmware.ICbase/PDF/vmware-data-protection-administration-...

Guest-level Backup and Restore
vSphere Data Protection Advanced supports guest-level backups for Microsoft SQL, Exchange, and Share
Point Servers. With guest-level backups, client agents (VMware VDP for SQL Server Client, VMware VDP for
Exchange Server Client, or VMware VDP for SharePoint Server Client) are installed on the SQL, Exchange, or
SharePoint Servers in the same manner that backup agents are typically installed on physical servers.

The advantages of VMware guest-level backups are:
- Provides a higher level of deduplication than image-level backups
- Provides additional application support for Microsoft SQL, Microsoft Exchange, or SharePoint Servers inside the virtual machines
- Support for backing up and restoring entire Microsoft SQL, Microsoft Exchange, or SharePoint Servers or selected databases
- Ability to support application consistent backups
- Identical backup methods for physical and virtual machines

VDP Advanced,  features:

Agents for mission-critical applications – A lightweight in-guest
agent communicates with the application’s backup APIs, delivering
application consistency and granular backup and recovery:

• Microsoft SQL Server agent delivers granular backup and
recovery of the entire application, of individual databases,
or only of logs.

• Microsoft Exchange Server agent delivers application-consistent
backup and granular recovery, and mailbox-level recovery.
Volume Shadow Copy (VSS) support enables consistent
backups of virtual machines running VSS-aware applications.

Regards,

P.

[vmb01]

Thanks.

If I backup a VM without client agent installed, so using VMware tools VSS is activated.

Is this backup application consistent or just crash consistent?

[snekkalapudi]

In such a case the backup is just a crash consistent one.

[vmb01]

thanks

why is just crash consistent? Can you explain me why the vss invoked from VMware tools is not able to set the applications in a consistent state?

thanks

[snekkalapudi]

Though VSS is enabled in agentless image level backup (VDP), application consistency is not guaranteed. There might be transactional data loss. But with VDPA(Agent based guest level backup), application consistency is guaranteed.

[jhunter1 · Accepted solution]

Backup will be application consistent assuming there is a VSS writer installed for the application. For example, when you install SQL Server, a VSS writer for SQL Server is automatically included. Oracle Database on Windows does not automatically install VSS (as far as I can remember - it has been a while). However, installing the VSS writer will enable application-consistent backups > Quiescing Oracle Database on Windows for Backup with VMware vSphere Data Protection Advanced | VMwar...

However, back to the SQL Server example, note that logs are not truncated when the VSS components in VMware Tools are used.

[vNEX]

Detailed info for Oracle and VSS can be found here:

http://docs.oracle.com/cd/B28359_01/win.111/b32010/vss.htm

MS Technet about VSS, quiescing, writers ...

http://technet.microsoft.com/en-us/library/ee923636(v=ws.10).aspx

Regards,

P.

[vNEX]

In addition to jhunter very precise answer just little bit theory from MS:

Writers

Writers are applications or services that store persistent information in files on disk and that provide the names and locations of these files to requesters by using the shadow copy interface.

During backup operations, writers ensure that their data is quiescent and stable—suitable for shadow copy and backup. Writers collaborate with restores by unlocking files when possible and indicating alternate locations when necessary.

If no writers are present during a VSS backup operation, a shadow copy can still be created. In this case, all data on the shadow-copied volume will be in the crash-consistent state.

For the reference about all in-box writers distributed with MS OS, se:

http://msdn.microsoft.com/en-us/library/windows/desktop/bb968827(v=vs.85).aspx

For example VDPA plugin for MS Exchange includes:

MS Exchange Store VSS writer

MS Exchange Replication VSS writer

Regards,

P.

[vmb01]

Thanks,

so it's rigt to say that :

A VSS writer for SQL Server is automatically included with the installation of SQL server:

so the backup products that invoke the VSS components in VMware Tools , will be application-consistent for SQL ( logs are not truncated).

For other applications it's necessary to verify if a VSS writer is installed and if it's run properly.