Disk Space Change

The Disk Space Change check compares each drive's current free space with an earlier reading and reports how much space was consumed or freed over a period you choose. This lets you spot a drive that is filling up unusually fast, even while it still has plenty of free space. To monitor how much space is currently free, use the Disk Space check. The check runs on Windows, Linux, and macOS (x64 and Arm64 each), every 60 minutes by default.

Steps

1. Go to Devices and open the device.
2. Click the Checks tab → Add Check → Disk Space Change.
3. Choose the drives, the Comparison period (hours), the direction under Alert on, and the thresholds.
4. Click Add Check.

Alternatively, assign the check with a config package.

Settings

• With Monitor all drives, the check only includes local fixed disks on Windows, not network, removable, or optical drives. On Linux and macOS it skips virtual file systems and system volumes.
• If a warning threshold is higher than the matching critical threshold, the check swaps the two values before evaluation.
• With Space freed you can detect, for example, that an unusually large amount of data was deleted.

Results

The check evaluates each drive separately. It compares the current free space with the oldest stored reading that is still inside the comparison period and only counts the direction chosen under Alert on.

The overall result is the worst result across all drives. If no drive is measured at all, for example because none is ready, the check reports Warning. Without any change in the chosen direction the result is always OK, even if you set a threshold to 0.

For each drive the check shows:

• Change in free space over the period, also as a share of capacity
• The period actually compared, in hours, and the resulting change per day
• Used, free, and total space
• When free space is shrinking, a projection of how many days until the drive is full (only when under 400 days)

Readings and baseline

• The device stores the readings itself. On the first run after assignment there is no earlier reading yet: the drive shows as OK with the hint "Collecting baseline…". A change can be reported from the second run onwards.
• Until readings cover the whole comparison period, the check compares with the first stored reading, so the period actually compared is shorter than configured.
• Readings are stored per comparison period. If you change Comparison period (hours), measurement starts over.

See also: Set up alerts for a check

FAQ

What does a negative disk space change mean?

The value describes the change in free space: a negative value means less free space, so space was consumed. A positive value means more free space, so space was freed.

For example, if free space drops from 90 GB to 65 GB, the change is −25 GB — 25 GB was consumed, not freed.

Whether this produces a warning or critical result depends on the direction selected under Alert on and your thresholds.