dmstats

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 operations.

--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 divided. 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 interrupted.

--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 update_filemap command, or by starting the daemon manually.

--follow follow_mode

Specify the dmfilemapd file following mode. The file map monitoring 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 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 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.

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 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.

-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 matching value. The default program ID for dmstats-managed 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 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 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 speficied 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 device(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 create 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 respectively, 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 device-mapper kernel statistics subsystem.

By default dmstats creates regions with a program_id of "dmstats".

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 database files.

To work with the --filemap option, files must be located on a local file system, backed by a device-mapper device, that supports 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 behaviour 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 extents allocated to the file change. This behaviour can be disabled 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 resources used by the region are released and the region will not appear in the output of subsequent list, print, or report operations.

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

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 identifiers. 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 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 objects. If the count argument is specified, the report will repeat at a fixed interval set by the --interval option. The default 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 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 allocated 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 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 counters 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 entire 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 reported 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 objects 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 exist in the sequence of region_id values for a particular device.

The region_id should be treated as an opaque identifier used to reference 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-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 automatically.

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 monitoring 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 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 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 values. 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.

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 using 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

Referenced By

dmfilemapd(8), dmsetup(8), lvm(8), lvmsadc(8), lvmsar(8), pmdadm(1).