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DMSTATS(8)                   MAINTENANCE COMMANDS                   DMSTATS(8)

NAME
       dmstats -- device-mapper statistics management

SYNOPSIS
       dmsetup stats command [OPTIONS]

       dmstats command device_name | --major major --minor minor | -u|--uuid
              uuid [-v|--verbose]
       dmstats clear device_name [--allprograms|--programid id]
              [--allregions|--regionid id]
       dmstats create device_name...|file_path...|--alldevices [--areas nr_ar-
              eas|--areasize area_size] [--bounds histogram_boundaries]
              [--filemap] [--follow follow_mode] [--foreground] [--nomonitor]
              [--nogroup] [--precise] [--start start_sector --length
              length|--segments] [--userdata user_data] [--programid id]
       dmstats delete device_name|--alldevices [--allprograms|--programid id]
              [--allregions|--regionid id]
       dmstats group [device_name|--alldevices] [--alias name] [--regions re-
              gions]
       dmstats help [-c|-C|--columns]
       dmstats list [device_name] [--histogram] [--allprograms|--programid id]
              [--units units] [--area] [--region] [--group] [--nosuffix]
              [--notimesuffix] [-v|--verbose]
       dmstats print [device_name] [--clear] [--allprograms|--programid id]
              [--allregions|--regionid id]
       dmstats report [device_name] [--interval seconds] [--count count]
              [--units units] [--histogram] [--allprograms|--programid id]
              [--allregions|--regionid id] [--area] [--region] [--group]
              [-O|--sort sort_fields] [-S|--select selection] [--units units]
              [--nosuffix] [--notimesuffix]
       dmstats ungroup [device_name|--alldevices] [--groupid id]
       dmstats update_filemap file_path [--groupid id] [--follow follow_mode]
              [--foreground]

DESCRIPTION
       The  dmstats program manages IO statistics regions for devices that use
       the device-mapper driver. Statistics regions may be  created,  deleted,
       listed and reported on using the tool.

       The first argument to dmstats is a command.

       The  second  argument  is the device name, uuid or major and minor num-
       bers.

       Further options permit the selection of regions, output format control,
       and reporting behaviour.

       When no device argument is given dmstats will by default operate on all
       device-mapper devices present. The create and delete  commands  require
       the use of --alldevices when used in this way.

OPTIONS
       --alias name
              Specify an alias name for a group.

       --alldevices
              If  no device arguments are given allow operation on all devices
              when creating or deleting regions.

       --allprograms
              Include regions from all program IDs for list and report  opera-
              tions.

       --allregions
              Include  all present regions for commands that normally accept a
              single region identifier.

       --area
              When peforming a list or report, include objects of type area in
              the results.

       --areas nr_areas
              Specify  the  number  of statistics areas to create within a new
              region.

       --areasize area_size[b|B|s|S|k|K|m|M|g|G|t|T|p|P|e|E]
              Specify the size of areas into which a new region should be  di-
              vided.  An optional suffix selects units of: (b)ytes, (s)ectors,
              (k)ilobytes, (m)egabytes, (g)igabytes, (t)erabytes, (p)etabytes,
              (e)xabytes.   Capitalise to use multiples of 1000 (S.I.) instead
              of 1024.

       --clear
              When printing statistics counters, also atomically reset them to
              zero.

       --count count
              Specify  the iteration count for repeating reports. If the count
              argument is zero reports will continue to  repeat  until  inter-
              rupted.

       --group
              When  peforming  a list or report, include objects of type group
              in the results.

       --filemap
              Instead of creating regions on a device as specified by  command
              line  options,  open  the file found at each file_path argument,
              and create regions corresponding to the locations of the on-disk
              extents allocated to the file(s).

       --nomonitor
              Disable  the  dmfilemapd  daemon  when  creating new file mapped
              groups. Normally the device-mapper  filemap  monitoring  daemon,
              dmfilemapd,  is started for each file mapped group to update the
              set of regions as the file changes on-disk: use of  this  option
              disables this behaviour.

              Regions  in  the  group  may  still  be  updated  with  the  up-
              date_filemap command, or by starting the daemon manually.

       --follow follow_mode
              Specify the dmfilemapd file following mode. The file  map  moni-
              toring  daemon  can monitor files in two distinct ways: the mode
              affects the behaviour of the daemon when a file under monitoring
              is  renamed or unlinked, and the conditions which cause the dae-
              mon to terminate.

              The follow_mode argument is  either  "inode",  for  follow-inode
              mode, or "path", for follow-path.

              If  follow-inode  mode  is  used,  the daemon will hold the file
              open, and continue to update regions from the same file descrip-
              tor.  This  means  that  the  mapping  will  follow rename, move
              (within the same file system), and unlink operations. This  mode
              is  useful  if the file is expected to be moved, renamed, or un-
              linked while it is being monitored.

              In follow-inode mode, the daemon will exit once it detects  that
              the file has been unlinked and it is the last holder of a refer-
              ence to it.

              If follow-path is used, the daemon  will  re-open  the  provided
              path  on  each  monitoring  iteration. This means that the group
              will be updated to reflect a new file being moved  to  the  same
              path  as  the  original file. This mode is useful for files that
              are expected to be updated via unlink and rename.

              In follow-path mode, the daemon will exit if the file is removed
              and not replaced within a brief tolerance interval.

              In  either mode, the daemon exits automatically if the monitored
              group is removed.

       --foreground
              Specify that the dmfilemapd daemon should run in the foreground.
              The  daemon  will not fork into the background, and will replace
              the dmstats command that started it.

       --groupid id
              Specify the group to operate on.

       --bounds histogram_boundaries[ns|us|ms|s]
              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.

       --histogram
              When used with the  report  and  list  commands  select  default
              fields that emphasize latency histogram data.

       --interval seconds
              Specify  the  interval  in seconds between successive iterations
              for repeating reports. If --interval is specified but --count is
              not, reports will continue to repeat until interrupted.

       --length length[b|B|s|S|k|K|m|M|g|G|t|T|p|P|e|E]
              Specify the length of a new statistics region in sectors. An op-
              tional suffix selects units of: (b)ytes, (s)ectors, (k)ilobytes,
              (m)egabytes,  (g)igabytes, (t)erabytes, (p)etabytes, (e)xabytes.
              Capitalise to use multiples of 1000 (S.I.) instead of 1024.

       -j|--major major
              Specify the major number.

       -m|--minor minor
              Specify the minor number.

       --nogroup
              When creating regions mapping the extents of a file in the  file
              system, do not create a group or set an alias.

       --nosuffix
              Suppress the suffix on output sizes.  Use with --units (except h
              and H) if processing the output.

       --notimesuffix
              Suppress the suffix on output time  values.  Histogram  boundary
              values will be reported in units of nanoseconds.

       -o|--options
              Specify which report fields to display.

       -O|--sort sort_fields
              Sort  output  according to the list of fields given. Precede any
              sort field with '-' for a reverse sort on that column.

       --precise
              Attempt to use nanosecond precision counters when  creating  new
              statistics regions.

       --programid id
              Specify  a  program  ID string. When creating new statistics re-
              gions this string is stored with the region.  Subsequent  opera-
              tions  may  supply  a program ID in order to select only regions
              with a matching value. The default program ID  for  dmstats-man-
              aged regions is "dmstats".

       --region
              When  peforming a list or report, include objects of type region
              in the results.

       --regionid id
              Specify the region to operate on.

       --regions region_list
              Specify a list of regions to group. The group list is  a  comma-
              separated  list  of  region identifiers. Continuous sequences of
              identifiers may be expressed as a hyphen  separated  range,  for
              example: '1-10'.

       --relative
              If  displaying  the  histogram report show relative (percentage)
              values instead of absolute counts.

       -S|--select selection
              Display only rows that match selection criteria. All  rows  with
              the  additional "selected" column (-o selected) showing 1 if the
              row matches the selection and 0 otherwise. The selection  crite-
              ria  are defined by specifying column names and their valid val-
              ues while making use of supported comparison operators.

       --start start[b|B|s|S|k|K|m|M|g|G|t|T|p|P|e|E]
              Specify the start offset of a new statistics region in  sectors.
              An   optional  suffix  selects  units  of:  (b)ytes,  (s)ectors,
              (k)ilobytes, (m)egabytes, (g)igabytes, (t)erabytes, (p)etabytes,
              (e)xabytes.   Capitalise to use multiples of 1000 (S.I.) instead
              of 1024.

       --segments
              When used with create, create a new statistics region  for  each
              target  contained in the given device(s). This causes a separate
              region to be allocated for each segment of the device.

              The newly created regions are automatically placed into a  group
              unless the --nogroup option is given. When grouping is enabled a
              group alias may be specified using the --alias option.

       --units [units][h|H|b|B|s|S|k|K|m|M|g|G|t|T|p|P|e|E]
              Set the display units for report output.  All sizes  are  output
              in    these   units:   (h)uman-readable,   (b)ytes,   (s)ectors,
              (k)ilobytes, (m)egabytes, (g)igabytes, (t)erabytes, (p)etabytes,
              (e)xabytes.   Capitalise to use multiples of 1000 (S.I.) instead
              of 1024.  Can also specify custom units e.g. --units 3M.

       --userdata user_data
              Specify user data (a word) to be stored with a new  region.  The
              value  is  added  to  any internal auxilliary data (for example,
              group information), and stored with the region in  the  aux_data
              field provided by the kernel. Whitespace is not permitted.

       -u|--uuid
              Specify the uuid.

       -v|--verbose [-v|--verbose]
              Produce additional output.

COMMANDS
       clear device_name [--allprograms|--programid id]
              [--allregions|--regionid id]
              Instructs the kernel to clear statistics counters for the spefi-
              cied regions (with the exception of in-flight IO counters).

       create device_name...|file_path...|--alldevices [--areas nr_areas|--ar-
              easize area_size] [--bounds histogram_boundaries] [--filemap]
              [--follow follow_mode] [--foreground] [--nomonitor] [--nogroup]
              [--precise] [--start start_sector --length length|--segments]
              [--userdata user_data] [--programid id]
              Creates  one or more new statistics regions on the specified de-
              vice(s).

              The region will  span  the  entire  device  unless  --start  and
              --length  or  --segments  are given. The --start an --length op-
              tions allow a region of arbitrary length to be placed at an  ar-
              bitrary  offset  into the device. The --segments option causes a
              new region to be created for each target  in  the  corresponding
              device-mapper device's table.

              If the --precise option is used the command will attempt to cre-
              ate a region using nanosecond precision counters.

              If --bounds is given a latency histogram will be tracked for the
              new  region. The boundaries of the histogram bins are given as a
              comma separated list of latency values.  There  is  an  implicit
              lower bound of zero on the first bin and an implicit upper bound
              of infinity (or the configured interval duration) on  the  final
              bin.

              Latencies  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 respec-
              tively, so for example, 10ms is equivalent to 10000000.  Latency
              values  with a precision of less than one milisecond can only be
              used when precise timestamps are enabled: if  --precise  is  not
              given  and  values  less than one milisecond are used it will be
              enabled automatically.

              An optional program_id or user_data  string  may  be  associated
              with the region. A program_id may then be used to select regions
              for subsequent list, print, and report operations. The user_data
              stores an arbitrary string and is not used by dmstats or the de-
              vice-mapper kernel statistics subsystem.

              By default dmstats creates regions with  a  program_id  of  "dm-
              stats".

              On  success the region_id of the newly created region is printed
              to stdout.

              If the --filemap option is given with a regular file, or list of
              files,  as  the  file_path argument, instead of creating regions
              with parameters specified on the command line, dmstats will open
              the  files located at file_path and create regions corresponding
              to the physical extents allocated to the file. This can be  used
              to  monitor  statistics for individual files in the file system,
              for example, virtual machine images, swap areas, or large  data-
              base files.

              To  work  with  the --filemap option, files must be located on a
              local file system, backed by a device-mapper device,  that  sup-
              ports  physical extent data using the FIEMAP ioctl (Ext4 and XFS
              for e.g.).

              By default regions that map a file are placed into a  group  and
              the  group alias is set to the basename of the file. This behav-
              iour can be overridden with the --alias and --nogroup options.

              Creating a group that maps a file automatically starts a daemon,
              dmfilemapd to monitor the file and update the mapping as the ex-
              tents allocated to the file change. This behaviour can  be  dis-
              abled using the --nomonitor option.

              Use  the  --group  option to only display information for groups
              when listing and reporting.

       delete device_name|--alldevices [--allprograms|--programid id]
              [--allregions|--regionid id]
              Delete  the  specified  statistics  region. All counters and re-
              sources used by the region are released and the region will  not
              appear in the output of subsequent list, print, or report opera-
              tions.

              All regions registered on a device may be removed using --allre-
              gions.

              To  remove  all  regions  on  all  devices both --allregions and
              --alldevices must be used.

              If a --groupid is given instead of a --regionid the command will
              attempt to delete the group and all regions that it contains.

              If  a  deleted  region is the first member of a group of regions
              the group will also be removed.

       group [device_name|--alldevices] [--alias name] [--regions regions]
              Combine one or more statistics regions on the  specified  device
              into a group.

              The  list  of  regions to be grouped is specified with --regions
              and an optional alias may be assigned with --alias. The  set  of
              regions  is  given  as  a comma-separated list of region identi-
              fiers. A continuous range of identifers spanning from R1  to  R2
              may be expressed as 'R1-R2'.

              Regions that have a histogram configured can be grouped: in this
              case the number of histogram bins and their  bounds  must  match
              exactly.

              On success the group list and newly created group_id are printed
              to stdout.

              The group metadata is stored with the  first  (lowest  numbered)
              region_id  in  the  group: deleting this region will also delete
              the group and other group members  will  be  returned  to  their
              prior state.

       help [-c|-C|--columns]
              Outputs  a summary of the commands available, optionally includ-
              ing the list of report fields.

       list [device_name] [--histogram] [--allprograms|--programid id]
              [--units units] [--area] [--region] [--group] [--nosuffix]
              [--notimesuffix] [-v|--verbose]
              List the statistics regions, areas, or groups registered on  the
              device.   If  the --allprograms switch is given all regions will
              be listed regardless of region program ID values.

              By default only regions and groups are included in list  output.
              If  -v  or --verbose is given the report will also include a row
              of information for each configured group and for each area  con-
              tained in each region displayed.

              Regions  that  contain a single area are by default omitted from
              the verbose list since their properties  are  identical  to  the
              area  that  they contain - to view all regions regardless of the
              number of areas present use --region). To also  view  the  areas
              contained within regions use --area.

              If  --histogram  is  given the report will include the bin count
              and latency boundary values for any configured histograms.

       print [device_name] [--clear] [--allprograms|--programid id]
              [--allregions|--regionid id]
              Print  raw  statistics  counters for the specified region or for
              all present regions.

       report [device_name] [--interval seconds] [--count count] [--units
              units] [--histogram] [--allprograms|--programid id]
              [--allregions|--regionid id] [--area] [--region] [--group]
              [-O|--sort sort_fields] [-S|--select selection] [--units units]
              [--nosuffix] [--notimesuffix]
              Start a report for the specified object or for all  present  ob-
              jects.  If  the count argument is specified, the report will re-
              peat at a fixed interval set by the --interval option.  The  de-
              fault interval is one second.

              If  the  --allprograms  switch  is  given,  all  regions will be
              listed, regardless of region program ID values.

              If the --histogram is given the report  will  include  the  his-
              togram values and latency boundaries.

              If  the  --relative is used the default histogram field displays
              bin values as a percentage of the total number of I/Os.

              Object types (areas, regions and groups) to include in  the  re-
              port  are  selected  using the --area, --region, and --group op-
              tions.

       ungroup [device_name|--alldevices] [--groupid id]
              Remove an existing group and return all the group's  regions  to
              their original state.

              The group to be removed is specified using --groupid.

       update_filemap file_path [--groupid id] [--follow follow_mode] [--fore-
              ground]
              Update a group of dmstats regions specified  by  group_id,  that
              were  previously  created with --filemap, either directly, or by
              starting the monitoring daemon, dmfilemapd.

              This will add and remove regions to reflect changes in the allo-
              cated  extents  of  the file on-disk, since the time that it was
              crated or last updated.

              Use of this command is not normally needed since the  dmfilemapd
              daemon  will  automatically  monitor  filemap groups and perform
              these updates when required.

              If a filemapped group was created with --nomonitor, or the  dae-
              mon  has been killed, the update_filemap can be used to manually
              force an update or start a new daemon.

              Use --nomonitor to force a direct update  and  disable  starting
              the monitoring daemon.

REGIONS, AREAS, AND GROUPS
       The device-mapper statistics facility allows separate performance coun-
       ters to be maintained for arbitrary regions of devices.  A  region  may
       span  any range: from a single sector to the whole device. A region may
       be further sub-divided into a number of distinct areas (one  or  more),
       each with its own counter set. In this case a summary value for the en-
       tire region is also available for use in reports.

       In addition, one or more regions on one device can be combined  into  a
       statistics group. Groups allow several regions to be aggregated and re-
       ported as a single entity; counters  for  all  regions  and  areas  are
       summed  and  used  to  report totals for all group members. Groups also
       permit the assignment of an optional alias, allowing  meaningful  names
       to be associated with sets of regions.

       The group metadata is stored with the first (lowest numbered) region_id
       in the group: deleting this region will also delete the group and other
       group members will be returned to their prior state.

       By default new regions span the entire device. The --start and --length
       options allows a region of any size to be placed at any location on the
       device.

       Using  offsets it is possible to create regions that map individual ob-
       jects within a block device (for example: partitions, files in  a  file
       system,  or stripes or other structures in a RAID volume). Groups allow
       several non-contiguous regions to be assembled together  for  reporting
       and data aggregation.

       A region may be either divided into the specified number of equal-sized
       areas, or into areas of the given size by specifying one of --areas  or
       --areasize when creating a region with the create command. Depending on
       the size of the areas and the device region the final area  within  the
       region may be smaller than requested.

       Region identifiers

       Each  region  is assigned an identifier when it is created that is used
       to reference the region in subsequent  operations.  Region  identifiers
       are unique within a given device (including across different program_id
       values).

       Depending on the sequence of create and delete operations, gaps may ex-
       ist in the sequence of region_id values for a particular device.

       The  region_id should be treated as an opaque identifier used to refer-
       ence the region.

       Group identifiers

       Groups are also assigned an integer identifier at creation  time;  like
       region  identifiers, group identifiers are unique within the containing
       device.

       The group_id should be treated as an opaque identifier used  to  refer-
       ence the group.

FILE MAPPING
       Using  --filemap,  it  is possible to create regions that correspond to
       the extents of a file in the file system. This allows IO statistics  to
       be monitored on a per-file basis, for example to observe large database
       files, virtual machine images, or other files of interest.

       To be able to use file mapping, the file must be backed  by  a  device-
       mapper device, and in a file system that supports the FIEMAP ioctl (and
       which returns data describing the physical location of  extents).  This
       currently includes xfs(5) and ext4(5).

       By default the regions making up a file are placed together in a group,
       and the group alias is set to the basename(3) of the file. This  allows
       statistics  to  be reported for the file as a whole, aggregating values
       for the regions making up the group. To see only the whole file (group)
       when using the list and report commands, use --group.

       Since  it is possible for the file to change after the initial group of
       regions is created, the update_filemap command, and  dmfilemapd  daemon
       are  provided to update file mapped groups either manually or automati-
       cally.

       File follow modes

       The file map monitoring daemon can monitor files in two distinct  ways:
       follow-inode mode, and follow-path mode.

       The mode affects the behaviour of the daemon when a file under monitor-
       ing is renamed or unlinked, and the conditions which cause  the  daemon
       to terminate.

       If  follow-inode  mode is used, the daemon will hold the file open, and
       continue to update regions from the same file  descriptor.  This  means
       that  the  mapping  will follow rename, move (within the same file sys-
       tem), and unlink operations. This mode is useful if  the  file  is  ex-
       pected to be moved, renamed, or unlinked while it is being monitored.

       In  follow-inode  mode,  the  daemon will exit once it detects that the
       file has been unlinked and it is the last holder of a reference to it.

       If follow-path is used, the daemon will re-open the  provided  path  on
       each monitoring iteration. This means that the group will be updated to
       reflect a new file being moved to the same path as the  original  file.
       This  mode  is useful for files that are expected to be updated via un-
       link and rename.

       In follow-path mode, the daemon will exit if the file  is  removed  and
       not replaced within a brief tolerance interval (one second).

       To stop the daemon, delete the group containing the mapped regions: the
       daemon will automatically shut down.

       The daemon can also be safely killed at any time and the group kept: if
       the file is still being allocated the mapping will become progressively
       out-of-date as extents are added and removed (in this case  the  daemon
       can be re-started or the group updated manually with the update_filemap
       command).

       See the create command and --filemap, --follow, and --nomonitor options
       for further information.

       Limitations

       The  daemon  attempts to maintain good synchronisation between the file
       extents and the regions contained in the group, however, since  it  can
       only  react  to  new allocations once they have been written, there are
       inevitably some IO events that cannot be counted when a file  is  grow-
       ing,  particularly  if  the  file  is being extended by a single thread
       writing beyond end-of-file (for example, the dd program).

       There is a further loss of events in that there is currently no way  to
       atomically  resize  a  dmstats  region and preserve its current counter
       values. This affects files when they grow by extending  the  final  ex-
       tent,  rather than allocating a new extent: any events that had accumu-
       lated in the region between any prior  operation  and  the  resize  are
       lost.

       File mapping is currently most effective in cases where the majority of
       IO does not trigger extent allocation. Future updates may address these
       limitations when kernel support is available.

REPORT FIELDS
       The dmstats report provides several types of field that may be added to
       the default field set, or used to create custom reports.

       All performance counters and metrics are calculated per-area.

   Derived metrics
       A number of metrics fields are included that provide high level perfor-
       mance indicators. These are based on the fields provided by the conven-
       tional Linux iostat program and are derived from the basic counter val-
       ues provided by the kernel for each area.

       reads_merged_per_sec
              Reads merged per second.

       writes_merged_per_sec
              Writes merged per second.

       reads_per_sec
              Reads completed per second.

       writes_per_sec
              Writes completed per second.

       read_size_per_sec
              Size of data read per second.

       write_size_per_sec
              Size of data written per second.

       avg_request_size
              Average request size.

       queue_size
              Average queue size.

       await  The average wait time for read and write operations.

       r_await
              The average wait time for read operations.

       w_await
              The average wait time for write operations.

       throughput
              The device throughput in operations per second.

       service_time
              The average service time (in milliseconds) for operations issued
              to the device.

       util   Percentage of CPU time during which I/O requests were issued  to
              the  device (bandwidth utilization for the device). Device satu-
              ration occurs when this value is close to 100%.

   Group, region and area meta fields
       Meta fields provide information about the  groups,  regions,  or  areas
       that the statistics values relate to. This includes the region and area
       identifier, start, length, and counts, as well as the  program  ID  and
       user data values.

       region_id
              Region  identifier.  This  is a non-negative integer returned by
              the kernel when a statistics region is created.

       region_start
              The region start location. Display units  are  selected  by  the
              --units option.

       region_len
              The  length  of  the  region.  Display units are selected by the
              --units option.

       area_id
              Area identifier. Area identifiers are assigned  by  the  device-
              mapper statistics library and uniquely identify each area within
              a region. Each ID corresponds to a distinct set  of  performance
              counters  for  that  area of the statistics region. Area identi-
              fiers are always monotonically increasing  within  a  region  so
              that  higher  ID  values  correspond to greater sector addresses
              within the area and no gaps in the sequence of  identifiers  ex-
              ist.

       area_start
              The  area  start  location.  Display  units  are selected by the
              --units option.

       area_len
              The length of the  area.  Display  units  are  selected  by  the
              --units option.

       area_count
              The number of areas in this region.

       program_id
              The program ID value associated with this region.

       user_data
              The user data value associated with this region.

       group_id
              Group identifier. This is a non-negative integer returned by the
              dmstats group command when a statistics group is created.

       interval_ns
              The estimated interval over which  the  current  counter  values
              have accumulated. The value is reported as an interger expressed
              in units of nanoseconds.

       interval
              The estimated interval over which  the  current  counter  values
              have  accumulated.  The  value  is  reported as a real number in
              units of seconds.

   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.

       read_count
              Count of reads completed this interval.

       reads_merged_count
              Count of reads merged this interval.

       read_sector_count
              Count of 512 byte sectors read this interval.

       read_time
              Accumulated duration of all read requests (ns).

       write_count
              Count of writes completed this interval.

       writes_merged_count
              Count of writes merged this interval.

       write_sector_count
              Count of 512 byte sectors written this interval.

       write_time
              Accumulated duration of all write requests (ns).

       in_progress_count
              Count of requests currently in progress.

       io_ticks
              Nanoseconds spent servicing requests.

       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 milliseconds 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  accumu-
              lating.

       read_ticks
              Nanoseconds spent servicing reads.

       write_ticks
              Nanoseconds spent servicing writes.

   Histogram fields
       Histograms measure the frequency distribution of user specified I/O la-
       tency intervals. Histogram bin boundaries are specified when  a  region
       is created.

       A  brief  representation  of the histogram values and latency intervals
       can be included in the report using these fields.

       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.

       hist_count_bounds
              A  list  of the histogram counts for the current statistics area
              in order of ascending latency value  including  bin  boundaries:
              each  count  is prefixed by the lower bound of the corresponding
              histogram bin.

       hist_count_ranges
              A list of the histogram counts for the current  statistics  area
              in  order  of  ascending latency value including bin boundaries:
              each count is prefixed by both the lower and upper bounds of the
              corresponding histogram bin.

       hist_percent
              A  list of the relative histogram values for the current statis-
              tics area in order of ascending latency value,  expressed  as  a
              percentage.  Each  value  represents the proportion of I/Os with
              latency times falling into that bin's time range during the sam-
              ple period.

       hist_percent_bounds
              A  list of the relative histogram values for the current statis-
              tics area in order of ascending latency value,  expressed  as  a
              percentage  and  including bin boundaries. Each value represents
              the proportion of I/Os with  latency  times  falling  into  that
              bin's  time  range during the sample period and is prefixed with
              the corresponding bin's lower bound.

       hist_percent_ranges
              A list of the relative histogram values for the current  statis-
              tics  area  in  order of ascending latency value, expressed as a
              percentage and including bin boundaries. Each  value  represents
              the  proportion  of  I/Os  with  latency times falling into that
              bin's time range during the sample period and is  prefixed  with
              the corresponding bin's lower and upper bounds.

       hist_bounds
              A  list of the histogram boundary values for the current statis-
              tics area in order of ascending latency value.  The  values  are
              expressed  in  whole units of seconds, miliseconds, microseconds
              or nanoseconds with a suffix indicating the unit.

       hist_ranges
              A list of the histogram bin ranges for  the  current  statistics
              area  in  order  of ascending latency value.  The values are ex-
              pressed as "LOWER-UPPER" in whole units of seconds, miliseconds,
              microseconds or nanoseconds with a suffix indicating the unit.

       hist_bins
              The number of latency histogram bins configured for the area.

EXAMPLES
       Create a whole-device region with one area on vg00/lvol1
       # dmstats create vg00/lvol1
       vg00/lvol1: Created new region with 1 area(s) as region ID 0

       Create a 32M region 1G into device d0
       # dmstats create --start 1G --length 32M d0
       d0: Created new region with 1 area(s) as region ID 0

       Create a whole-device region with 8 areas on every device
       # dmstats create --areas 8
       vg00-lvol1: Created new region with 8 area(s) as region ID 0
       vg00-lvol2: Created new region with 8 area(s) as region ID 0
       vg00-lvol3: Created new region with 8 area(s) as region ID 0
       vg01-lvol0: Created new region with 8 area(s) as region ID 2
       vg01-lvol1: Created new region with 8 area(s) as region ID 0
       vg00-lvol2: Created new region with 8 area(s) as region ID 1

       Delete all regions on all devices
       # dmstats delete --alldevices --allregions

       Create a whole-device region with areas 10GiB in size on vg00/lvol1 us-
       ing dmsetup
       # dmsetup stats create --areasize 10G vg00/lvol1
       vg00-lvol1: Created new region with 5 area(s) as region ID 1

       Create a 1GiB region with 16 areas at the start of vg00/lvol1
       # dmstats create --start 0 --len 1G --areas=16 vg00/lvol1
       vg00-lvol1: Created new region with 16 area(s) as region ID 0

       List the statistics regions registered on vg00/lvol1
       # dmstats list vg00/lvol1
       Name             RgID  RStart RSize  #Areas ASize  ProgID
       vg00-lvol1           0      0 61.00g      1 61.00g dmstats
       vg00-lvol1           1 61.00g 19.20g      1 19.20g dmstats
       vg00-lvol1           2 80.20g  2.14g      1  2.14g dmstats

       Display five statistics reports for vg00/lvol1 at an  interval  of  one
       second
       # dmstats report --interval 1 --count 5 vg00/lvol1
       # dmstats report
       Name              RgID  ArID  AStart ASize  RRqM/s   WRqM/s   R/s   W/s
       RSz/s WSz/s   AvRqSz  QSize Util%      AWait RdAWa WrAWa
       vg_hex-lv_home       0     0       0  61.00g      0.00      0.00   0.00
       218.00     0   1.04m   4.50k  2.97      81.70 13.62  0.00 13.62
       vg_hex-lv_home        1      0  61.00g  19.20g      0.00     0.00  0.00
       5.00     0 548.00k 109.50k  0.14      11.00 27.40  0.00 27.40
       vg_hex-lv_home       2     0  80.20g   2.14g      0.00      0.00   0.00
       14.00     0   1.15m  84.00k  0.39      18.70 27.71  0.00 27.71

       Create one region for reach target contained in device vg00/lvol1
       # dmstats create --segments vg00/lvol1
       vg00-lvol1: Created new region with 1 area(s) as region ID 0
       vg00-lvol1: Created new region with 1 area(s) as region ID 1
       vg00-lvol1: Created new region with 1 area(s) as region ID 2

       Create  regions  mapping  each  file in the directory images/ and place
       them into separate groups, each named after the corresponding file
       # dmstats create --filemap images/*
       images/vm1.qcow2: Created new group with 87 region(s) as group ID 0.
       images/vm1-1.qcow2: Created new group with 8 region(s) as group ID 87.
       images/vm2.qcow2: Created new group with 11 region(s) as group ID 95.
       images/vm2-1.qcow2: Created new group with 1454 region(s) as  group  ID
       106.
       images/vm3.img: Created new group with 2 region(s) as group ID 1560.

       Print raw counters for region 4 on device d0
       # dmstats print --regionid 4 d0
       2097152+65536 0 0 0 0 29 0 264 701 0 41 701 0 41

AUTHORS
       Bryn M. Reeves <bmr@redhat.com>

SEE ALSO
       dmsetup(8)

       LVM2 resource page: https://www.sourceware.org/lvm2/
       Device-mapper resource page: http://sources.redhat.com/dm/

       Device-mapper statistics kernel documentation
       Documentation/device-mapper/statistics.txt

Linux                             Jun 23 2016                       DMSTATS(8)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | COMMANDS | REGIONS, AREAS, AND GROUPS | FILE MAPPING | REPORT FIELDS | EXAMPLES | AUTHORS | SEE ALSO