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.

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.

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.

Config options

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.

Config

jobs:
  - name: dmcache
    update_every: 5  # Collect DMCache statistics every 5 seconds

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.d directory, usually at /usr/libexec/netdata/plugins.d/. If that's not the case on your system, open netdata.conf and look for the plugins setting under [directories].

  cd /usr/libexec/netdata/plugins.d/

• Switch to the netdata user.

  sudo -u netdata -s

• Run the go.d.plugin to 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