The monitor reports a warning when the free space (including both already allocated space and free space on the media) drops below the Warning Threshold setting, expressed as percentage of the sum of data size plus disk free space. The monitor reports a critical alert when the free space drops below the Critical Threshold. Note that this monitor is disabled by default. Use overrides to enable it when necessary.
Knowledge Base article:
Summary
The monitor oversees the space available in the log file and on the media that hosts the log file. The space available on the media is considered part of free space if autogrowth is enabled for at least one of the files.
Causes
An unhealthy state is caused by having low free space across all log files. Low free space can be caused by:
Inadequate file configuration settings (size, max size, autogrowth, etc.)
Inadequate space left on media
Lack of periodic regular backups
Log not truncating
Use the following links to view the performance data: DB File Log Free Space Performance Data
This monitor aggregates the space available for each log file within a database depending on each file’s configuration:
No Autogrowth
For a file that has no autogrowth, free space would be the difference between the initial size for a file and the used space.
Autogrowth Enabled
For a file with autogrowth, free space would be calculated as the available free disk space that can be used for extension of the database file with respect to the last autogrowth step size. Because the last autogrowth step size can exceed disk capacity, calculations of the free space are performed as a function of autogrowth step values. For example, if autogrowth is set to 20% on the disk, the size of which is 10 GB and the current database size is 9 GB, the free space will be displayed as 0 GB because the last gigabyte cannot be used.
Low free space for database files that have autogrowth could mean that the file is approaching the limits of the hosting logical drive. For files with autogrowth enabled with a max size, low free space could also mean that the file is approaching the max size specified for a file.
The free space calculations also take into account that the file can also fail to grow if the growth amount of the file is greater than the amount left on disk and that the file cannot grow if the difference between the max size and the current file size is less than the growth amount. In these situations, available free space left on disk is not included as part of the free space because we cannot grow any longer.
Resolutions
This issue may be resolved by either:
Increasing the allocated size for log files if autogrowth is disabled
Increasing the max size value for a log file if autogrowth is enabled
Enabling autogrowth for at least one file
Moving log files to another drive with more free space if growth space is limited
Performing regular backups of log files for FULL and BULK-LOGGED recovery modes
Investigate why log is not getting truncated:
Long open running active transactions
Long running backup operations
Replicated transaction open for a long time (Transactional Replication)
Mirror lagging behind principal server (Database Mirroring)
Modifying the thresholds for this monitor to suit the workload
Alternatively if log file free space is not a concern for the database:
Disable this monitor for this specific database or all databases
The maximum size of data file stored in Azure BLOB Storage. The workflow will consider this value as a maximum storage capacity for each file.
1048576
Critical Threshold
The monitor will change its state to Critical if the value drops below this threshold. Being between this threshold and the warning threshold (inclusive) will result in the monitor being in a warning state.
10
Enabled
Enables or disables the workflow.
No
Generates Alerts
Defines whether the workflow generates an Alert.
No
Interval (seconds)
The recurring interval of time in seconds in which to run the workflow.
900
Synchronization Time
The synchronization time specified by using a 24-hour format. May be omitted.
Timeout (seconds)
Specifies the time the workflow is allowed to run before being closed and marked as failed.
300
Timeout for query execution (seconds)
The workflow will fail and register an event, if the query execution takes longer than the specified period.
60
Timeout for database connection (seconds)
The workflow will fail and register an event, if it cannot access the database during the specified period.
15
Warning Threshold
The monitor will change its state to Warning if the value drops below this threshold.
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