DMCache devices
DMCache devices
Plugin: go.d.plugin Module: dmcache
Overview
This collector monitors DMCache, providing insights into capacity usage, efficiency, and activity. It relies on the dmsetup CLI tool but avoids directly executing the binary. Instead, it utilizes ndsudo, a Netdata helper specifically designed to run privileged commands securely within the Netdata environment. This approach eliminates the need to use sudo, improving security and potentially simplifying permission management.
This collector is supported on all platforms.
This collector only supports collecting metrics from a single instance of this integration.
Default Behavior
Auto-Detection
This integration doesn’t support auto-detection.
Limits
The default configuration for this integration does not impose any limits on data collection.
Performance Impact
The default configuration for this integration is not expected to impose a significant performance impact on the system.
Setup
Prerequisites
No action required.
Configuration
File
The configuration file name for this integration is go.d/dmcache.conf.
You can edit the configuration file using the edit-config script from the
Netdata config directory.
cd /etc/netdata 2>/dev/null || cd /opt/netdata/etc/netdata
sudo ./edit-config go.d/dmcache.conf
Options
The following options can be defined globally: update_every.
| Name | Description | Default | Required |
|---|---|---|---|
| update_every | Data collection frequency. | 10 | no |
| timeout | dmsetup binary execution timeout. | 2 | no |
Examples
Custom update_every
Allows you to override the default data collection interval.
jobs:
- name: dmcache
update_every: 5 # Collect DMCache statistics every 5 seconds
Metrics
Metrics grouped by scope.
The scope defines the instance that the metric belongs to. An instance is uniquely identified by a set of labels.
Per dmcache device
These metrics refer to the DMCache device.
Labels:
| Label | Description |
|---|---|
| device | Device name |
Metrics:
| Metric | Dimensions | Unit |
|---|---|---|
| dmcache.device_cache_space_usage | free, used | bytes |
| dmcache.device_metadata_space_usage | free, used | bytes |
| dmcache.device_cache_read_efficiency | hits, misses | requests/s |
| dmcache.device_cache_write_efficiency | hits, misses | requests/s |
| dmcache.device_cache_activity | promotions, demotions | bytes/s |
| dmcache.device_cache_dirty_size | dirty | bytes |
Alerts
There are no alerts configured by default for this integration.
Troubleshooting
Debug Mode
Important: Debug mode is not supported for data collection jobs created via the UI using the Dyncfg feature.
To troubleshoot issues with the dmcache collector, run the go.d.plugin with the debug option enabled. The output
should give you clues as to why the collector isn’t working.
-
Navigate to the
plugins.ddirectory, usually at/usr/libexec/netdata/plugins.d/. If that’s not the case on your system, opennetdata.confand look for thepluginssetting under[directories].cd /usr/libexec/netdata/plugins.d/ -
Switch to the
netdatauser.sudo -u netdata -s -
Run the
go.d.pluginto debug the collector:./go.d.plugin -d -m dmcache
Getting Logs
If you’re encountering problems with the dmcache collector, follow these steps to retrieve logs and identify potential issues:
- Run the command specific to your system (systemd, non-systemd, or Docker container).
- Examine the output for any warnings or error messages that might indicate issues. These messages should provide clues about the root cause of the problem.
System with systemd
Use the following command to view logs generated since the last Netdata service restart:
journalctl _SYSTEMD_INVOCATION_ID="$(systemctl show --value --property=InvocationID netdata)" --namespace=netdata --grep dmcache
System without systemd
Locate the collector log file, typically at /var/log/netdata/collector.log, and use grep to filter for collector’s name:
grep dmcache /var/log/netdata/collector.log
Note: This method shows logs from all restarts. Focus on the latest entries for troubleshooting current issues.
Docker Container
If your Netdata runs in a Docker container named “netdata” (replace if different), use this command:
docker logs netdata 2>&1 | grep dmcache