I/O is frozen on database.

Applies to: SQL Server 2012, third-party backup software.
 

Problem Description.
 

After installing a third-party backup software and use it to backup SQL Server databases, you may start to see below messages appearing on SQL Server error log:


Event Type: Information
Event Source: MSSQLSERVER
Event Category: (2)
Event ID: 3197
Description:
I/O is frozen on database test. No user action is required. However, if I/O is not resumed promptly, you could cancel the backup.


Event Type: Information
Event Source: MSSQLSERVER
Event Category: (2)
Event ID: 3198
Description:
I/O was resumed on database test. No user action is required.


Cause.

This is normal behavior of backup software that relies on VSS to take backups.


"In the snapshot creation phase, we do the following:

a) SQL Writer talks to SQL Server to prepare for a snapshot backup

b) Then all I/O for the database being backed up is frozen, and then we create the snapshot.

c) Once this is done, the I/O is resumed. This process is called thaw."

Source: INFORMATIONAL: SHEDDING LIGHT on VSS & VDI Backups in SQL Server.
 

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