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NAME | DESCRIPTION | INSTALLATION | FILES | dmstats metric | PCP ENVIRONMENT | SEE ALSO | COLOPHON |
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PMDADM(1) General Commands Manual PMDADM(1)
pmdadm - Device Mapper PMDA
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
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.
$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
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
When creating the statistics regions with specified histogram
boundaries as below:
# 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.
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.
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 %%%SH%%%
# 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
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).
pmcd(1), pmstore(1), dmsetup(8), and dmstats(8).
This page is part of the PCP (Performance Co-Pilot) project.
Information about the project can be found at ⟨http://www.pcp.io/⟩.
If you have a bug report for this manual page, send it to
pcp@groups.io. This page was obtained from the project's upstream
Git repository ⟨https://github.com/performancecopilot/pcp.git⟩ on
2018-02-02. (At that time, the date of the most recent commit that
was found in the repository was 2018-02-02.) If you discover any
rendering problems in this HTML version of the page, or you believe
there is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
Performance Co-Pilot PCP PMDADM(1)
Pages that refer to this page: pcp-dmcache(1)
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