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   dmstats    ( 8 )

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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 performance indicators. These are based on the fields provided by the conventional Linux iostat program and are derived from the basic counter values 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 saturation 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 identifiers 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 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 accumulating.

read_ticks Nanoseconds spent servicing reads.

write_ticks Nanoseconds spent servicing writes.

Histogram fields Histograms measure the frequency distribution of user specified I/O latency 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 statistics 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 sample period.

hist_percent_bounds A list of the relative histogram values for the current statistics 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 statistics 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 statistics 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 expressed 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.