Collecting Volume Metrics

You can collect the following volume metrics on MapR-FS after enabling metrics collection as described in Enabling Volume Metric Collection:

Read I/Os number of reads
Write I/Os number of writes
Read throughput amount of data read
Write throughput amount of data written
Read latency amount of time taken by read operations
Write latency amount of time taken by write operations

If metrics collection is enabled on a volume, for each MapR-FS instance, on every node where the volume containers reside, metrics for the volume (for a day) are captured every 10 seconds and logged to files in a local volume, which is two way replicated. The metrics log file, Metrics.log-<date>-<n>.json, is available at /var/mapr/local/<hostname>/audit/<mfs-port> directory. Here:

  • mfs-port is the port on which the MapR-FS instance listens.
  • date is the record date in the format yyyy-mm-dd. A new file is created at the beginning of each day.
  • n is the iteration of the log file represented by 3 digits. A new file is created every time Warden is restarted on the node. For the first file, <n> is 001 and <n> is incremented every time warden restarts. For example: Metrics.log-2017-08-18-001.json and Metrics.log-2017-08-18-002.json

Each record in the file may look similar to the following:



  • ts — timestamp in milliseconds
  • vid — volume ID
  • RDT — read throughput in KB (cumulative for 10 seconds)
  • RDL — amount of time taken by read operations (average for 10 seconds)
  • RDO — number of read operations (cumulative for 10 seconds)
  • WRT — write throughput in KB (cumulative for 10 seconds)
  • WRL — amount of time taken by write operations (average for 10 seconds)
  • WRO — number of write operations (cumulative for 10 seconds)

When a new file is created, the old file is compressed by hoststats after 2 days, if hoststats is running on that node and if there are no further writes to the file, and the original file is deleted. If hoststats in not running on a node, the original JSON file is not compressed and is purged after 30 days retention period.

The collectd service reads from each file up to 16 MB of data every ten seconds, aggregates and writes one minute worth of data to OpenTSDB. When reading the file, the collectd service stores offsets (as to how much has been read) as extended attributes (trusted.disptachedOffset) on the file. In addition to the default tags assigned to each metric when collectd writes metrics to OpenTSDB, the following tags are assigned to volume metrics:

  • mapr.volmetrics.[read_|write_][throughput|latency|ops] — Displays the type of metric
  • volume_name — Displays the name of the volume

For more information on the default tags, see Metric Collection.

For each metrics file, MapR also creates a file, Vollist_metrics.log-<date>-<n>, in the /var/mapr/local/<hostname>/audit/<mfs-port>/ directory. This file contains a comma separated list of volume name and volume ID (for volumes for which metrics are captured) and is associated with the Metrics.log-<date><n>.json file. For example, the record in the file looks similar to the following:

<volumeid>,<volume name>,<volumeid>,<volume name>,...

You can visualize the metrics in the dashboards on Grafana. See Metric Visualization for more information.