Interpreting the data rows

This section explains the raw data in the individual data rows of the statistics. Use the dasdstat command to obtain more structured data.

start_time

is the UNIX epoch time stamp when data gathering was started or when the counters were last reset.

Tip: Use the date tool to convert the time stamp to a more readily human-readable format. See the date man page for details.

Single counters

have a single integer as the statistics data. All rows with labels that begin with total_ are of this data type.

The following rows show data for the sum of all requests, read and write:

total_requests

is the number of requests that have been processed.

total_sectors

is the sum of the sizes of all requests, in units of 512-byte sectors.

total_pav

is the number of requests that were processed through a PAV alias device.

total_hpf

is the number of requests that used High Performance FICON®.

The following rows show data for read requests only:

total_read_requests

is the number of read requests that have been processed.

total_read_sectors

is the sum of the sizes of all read requests, in units of 512-byte sectors.

total_read_pav

is the number of read requests that were processed through a PAV alias device.

total_read_hpf

is the number of read requests that used High Performance FICON.

Linear histograms

have a series of 32 integers as the statistics data. The integers represent a histogram, with a linear scale, of the number of requests in the request queue each time a request has been queued. The first integer shows how often the request queue contained zero requests, the second integer shows how often the queue contained one request, and the n-th value shows how often the queue contained n-1 requests.

histogram_ccw_queue_length

is the histogram data for all requests, read and write.

histogram_read_ccw_queue_length

is the histogram data for read requests only.

Logarithmic histograms

have a series of 32 integers as the statistics data. The integers represent a histogram with a logarithmic scale:

• The first integer always represents all measures of fewer than 4 units
• The second integer represents measures of 4 or more but less than 8 units
• The third integer represents measures of 8 or more but less than 16 units
• The n-th integer (1 < n < 32) represents measures of 2ⁿ or more but less than 2ⁿ⁺¹ units
• The 32nd integer represents measures of 2³² (= 4G = 4,294,967,296) units or more.

The following rows show data for the sum of all requests, read and write:

histogram_sectors

is the histogram data for request sizes. A unit is a 512-byte sector.

histogram_io_times

is the histogram data for the total time that is needed from creating the cqr to its completion in the DASD device driver and return to the block layer. A unit is a microsecond.

histogram_io_times_weighted

is the histogram data of the total time, as measured for histogram_io_times, devided by the requests size in sectors. A unit is a microsecond per sector.

This metric is deprecated and there is no corresponding histogram data for read requests.

histogram_time_build_to_ssch

is the histogram data of the time that is needed from creating the cqr to submitting the request to the subchannel. A unit is a microsecond.

histogram_time_ssch_to_irq

is the histogram data of the time that is needed from submitting the request to the subchannel until an interrupt indicates that the request has been completed. A unit is a microsecond.

histogram_time_ssch_to_irq_weighted

is the histogram data of the time that is needed from submitting the request to the subchannel until an interrupt indicates that the request has been completed, divided by the request size in 512-byte sectors. A unit is a microsecond per sector.

This metric is deprecated and there is no corresponding histogram data for read requests.

histogram_time_irq_to_end

is the histogram data of the time that is needed from return of the request from the channel subsystem, until the request is returned to the block layer. A unit is a microsecond.

The following rows show data for read requests only:

histogram_read_sectors

is the histogram data for read request sizes. A unit is a 512 byte sector.

histogram_read_io_times

is the histogram data, for read requests, for the total time needed from creating the cqr to its completion in the DASD device driver and return to the block layer. A unit is a microsecond.

histogram_read_time_build_to_ssch

is the histogram data, for read requests, of the time needed from creating the cqr to submitting the request to the subchannel. A unit is a microsecond.

histogram_read_time_ssch_to_irq

is the histogram data, for read requests, of the time needed from submitting the request to the subchannel until an interrupt indicates that the request has been completed. A unit is a microsecond.

histogram_read_time_irq_to_end

is the histogram data, for read requests, of the time needed from return of the request from the channel subsystem, until the request is returned to the blocklayer. A unit is a microsecond.