PMDADM(1)

NAME
pmdadm - Device Mapper PMDA

DESCRIPTION
pmdadm is a Performance Metrics Domain Agent (PMDA) which exports metric values for Device Mapper on the local system.

This PMDA collects its data through the dmsetup(8) utility, dmstats API and requires that the program is installed in order to function.

In addition, at least a statistics region must be created to use dmstats(8) in order to get the basic counter value.

Further details on device mapper can be found at http://redhat.com

INSTALLATION
Install the DM PMDA by using the Install script as root:

      # cd $PCP_PMDAS_DIR/dm
      # ./Install

To uninstall, do the following as root:

      # cd $PCP_PMDAS_DIR/dm
      # ./Remove

pmdadm is launched by pmcd(1) and should never be executed directly. The Install and Remove scripts notify pmcd when the agent is installed or removed.

FILES

$PCP_PMDAS_DIR/dm/help
    default help text file for the dm metrics

$PCP_PMDAS_DIR/dm/Install
    installation script for the pmdadm agent

$PCP_PMDAS_DIR/dm/Remove
    undo installation script for the pmdadm agent

$PCP_LOG_DIR/pmcd/dm.log
    default log file for error messages from pmdadm

dmstats metric
This PMDA use the dmstats API (the userspace device-mapper support library) to allow dmstats performance data.
Using this PMDA, users need the userspace device-mapper support library (libdevmapper) and the userspace command line tool (dmstats). Before getting the statistics metric, statistics regions have to be created. When creating the statistics regions of all device-mapper device under /dev/mapper as below:

    # dmstats create --alldevices

Further Detail on dmstats(8) can be found at man page.

Basic Counters
    Basic counters provide access to the raw counter data from the kernel, allowing further processing to be carried out by another program.
    The Kernel provides thirteen separate counters for each statistics area. The first eleven of these match the counters provided in /proc/diskstats or /sys/block/*/*/stat. The final pair provide separate counters for read and write time.

    dmstats.read
        Count of reads completed this interval per device-mapper device.

    dm.reads_merged
        Count of reads merged this interval per device-mapper device.

    dmstats.read_bytes
        Count of kbytes read this interval per device-mapper device.

    dmstats.reads_time
        Accumulated duration of all read requests per device-mapper device.

    dmstats.write
        Count of writes completed this interval per device-mapper device.

    dmstats.writes_merged
        Count of writes completed this interval per device-mapper device.

    dmstats.write_bytes
        Count of kbytes write this interval per device-mapper device.

    dmstats.writes_time
        Accumulated duration of all write requests per device-mapper device.

    dmstats.in_progress
        Count of requests currently in progress per device-mapper device.

    dmstats.io_ticks
        Nanoseconds spent servicing request per device-mapper device.

    dmstats.queue_ticks
        This field is incremented at each I/O start, I/O completion, I/O merge, or read of these stats by the number of I/Os in progress multiplied by the number of nanoseconds spent doing I/O since the last update of this field. This can provide an easy measure of both I/O completion time and the backlog that may be accumulating.

    dmstats.read_ticks
        Nanoseconds spent servicing reads per device-mapper device.

    dmstats.write_ticks
        Nanoseconds spent servicing writes per device-mapper device.

PCP ENVIRONMENT
Environment variables with the prefix PCP_ are used to parameterize the file and directory names used by PCP. On each installation, the file /etc/pcp.conf contains the local values for these variables. The $PCP_CONF variable may be used to specify an alternative configuration file, as described in pcp.conf(5).

SEE ALSO
pmcd(1), pmstore(1), dmsetup(8), and dmstats(8).