Ubuntu Manpage: pmdadm - Device Mapper PMDA

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  and  the  dmstats  API  and
       requires  that  the  program is installed in order to function.  In addition, at least one
       statistics region must be created using the dmstats(8)  utility  in  order  to  get  basic
       counter values.  See below for examples.

       Note  that  device-mapper  statistics  collection  is  not  enabled  by default and is not
       persistent across reboots (unless a system administrator has configured something  to  run
       in  rc.local  or  equivalent).   This  is  because  there  are  overheads  associated with
       statistics collection.  In addition, the pmdadm PMDA does  not  automatically  enable  any
       statistics collection because it may not be the only consumer of the data.

INSTALLATION

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

           # cd $PCP_PMDAS_DIR/dm
           # ./Install

       To uninstall, the following must be done 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.

CONFIGURATION

       This PMDA uses the dmstats API (the userspace device-mapper support  library)  to  capture
       device-mapper performance data.
       Using this PMDA, users need the userspace device-mapper support library (libdevmapper) and
       the userspace  command  line  tool  dmstats(8).   Before  device-mapper  metrics  will  be
       available  for  PCP,  statistics regions have to be created.  For example, to enable basic
       statistics for all local device-mapper logical devices, use the following command:

            # dmstats create --alldevices

       To create statistics regions with specified histogram boundaries, use the following:

            # dmstats create --alldevices --bounds histogram_boundaries

       Specify the boundaries of a latency histogram to be tracked for  the  region  as  a  comma
       separated  list  of  latency  values. Latency values are given in nanoseconds. An optional
       unit suffix of ns, us, ms, or s may  be  given  after  each  value  to  specify  units  of
       nanoseconds, microseconds, miliseconds or seconds respectively.  For example,

            # dmstats create --alldevices --bounds 10us,30us,50us,70us,90us

       Further details and more complex examples can be found in dmstats(8).

METRICS

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.

dmstats.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.

Histogram fields
Histograms measure the frequency distribution of user specified I/O latency intervals.
Histogram bin boundaries are specified when a region is created.
Instance name represents devicename, region id and bin boundaries.

dmstats.histogram.hist_count
A list of the histogram counts for the current statistics area in order of
ascending latency value. Each value represents the number of I/Os with latency
times falling into that bin's time range during the sample period.

dmstats.histogram.hist.bins
The number of latency histogram bins configured for the area.

EXAMPLES

       # dmstats create looptest0 --bounds 10us,30us,50us
       looptest0: Created new region with 1 area(s) as region ID 0

       # pminfo -f dmstats.read dmstats.histogram.hist_count

       dmstats.read
           inst [0 or "looptest0"] value 4099

       dmstats.histogram.hist_count
           inst [0 or "looptest0:0:0s"] value 1
           inst [1 or "looptest0:0:10us"] value 3752
           inst [2 or "looptest0:0:30us"] value 250
           inst [3 or "looptest0:0:50us"] value 96

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

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).