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_areas|--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
regions]
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 numbers.
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 performing 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 re-
gion.
--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 interrupt-
ed.
--group
When performing 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 ex-
tents allocated to the file(s).
--nomonitor
Disable the dmfilemapd daemon when creating new file mapped
groups. Normally the device-mapper filemap monitoring daemon, dm-
filemapd, is started for each file mapped group to update the set
of regions as the file changes on-disk: use of this option dis-
ables this behaviour.
Regions in the group may still be updated with the update_filemap
command, or by starting the daemon manually.
--follow follow_mode
Specify the dmfilemapd file following mode. The file map monitor-
ing daemon can monitor files in two distinct ways: the mode af-
fects the behaviour of the daemon when a file under monitoring is
renamed or unlinked, and the conditions which cause the daemon 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 descriptor.
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 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 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, milliseconds 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 regions
this string is stored with the region. Subsequent operations may
supply a program ID in order to select only regions with a match-
ing value. The default program ID for dmstats-managed regions is
"dmstats".
--region
When performing 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 ex-
ample: '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 criteria
are defined by specifying column names and their valid values
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 auxiliary 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 speci-
fied regions (with the exception of in-flight IO counters).
create device_name...|file_path...|--alldevices [--areas
nr_areas|--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]
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 options
allow a region of arbitrary length to be placed at an arbitrary
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 low-
er 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, milliseconds or seconds respective-
ly, so for example, 10 ms is equivalent to 10,000,000. Latency
values with a precision of less than one millisecond can only be
used when precise timestamps are enabled: if --precise is not
given and values less than one millisecond 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 lo-
cal file system, backed by a device-mapper device, that supports
physical extent data using the FIEMAP ioctl (e.g. Ext4 and XFS).
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 re-
gions is given as a comma-separated list of region identifiers. A
continuous range of identifiers spanning from R1 to R2 may be ex-
pressed 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 ex-
actly.
On success the group list and newly created group_id are printed
to stdout.
The group metadata is stored with the first (lowest numbered) re-
gion_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 including
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 contained
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 repeat
at a fixed interval set by the --interval option. The default in-
terval 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 histogram
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 report
are selected using the --area, --region, and --group options.
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]
[--foreground]
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
created 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 daemon
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 associ-
ated 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 val-
ues).
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 reference
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-map-
per 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 system),
and unlink operations. This mode is useful if the file is expected 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 unlink
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 synchronization 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 in-
evitably some IO events that cannot be counted when a file is growing,
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 val-
ues. This affects files when they grow by extending the final extent,
rather than allocating a new extent: any events that had accumulated 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 satura-
tion 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 iden-
tifier, 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-map-
per 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 identifiers
are always monotonically increasing within a region so that high-
er ID values correspond to greater sector addresses within the
area and no gaps in the sequence of identifiers exist.
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 integer 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 num-
ber 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 his-
togram 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 cor-
responding 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 la-
tency times falling into that bin's time range during the sample
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 cor-
responding 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 cor-
responding 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, milliseconds, 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, milliseconds,
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 32 MiB region 1 GiB 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 10 GiB 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 1 GiB 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: ]8;;https://www.sourceware.org/lvm2\https://www.sourceware.org/lvm2]8;;\
Device-mapper resource page: ]8;;http://www.sourceware.org/dm\http://www.sourceware.org/dm]8;;\
Device-mapper statistics kernel documentation
Documentation/device-mapper/statistics.txt
Linux Jun 23 2016 DMSTATS(8)
Generated by dwww version 1.16 on Tue Dec 16 04:57:48 CET 2025.