Ubuntu Manpage: tapestat - Report tape statistics.

Provided by: sysstat_12.7.5-2ubuntu1_amd64

NAME

       tapestat - Report tape statistics.

SYNOPSIS

       tapestat [ -k | -m ] [ -t ] [ -V ] [ -y ] [ -z ] [ --human ] [ interval [ count ] ]

DESCRIPTION

       The tapestat command is used for monitoring the activity of tape drives connected to a system.

       The  first  report  generated  by  the tapestat command provides statistics concerning the time since the
       system was booted, unless the -y option is used, when this first  report  is  omitted.   Each  subsequent
       report covers the time since the previous report.

       The  interval  parameter specifies the amount of time in seconds between each report. The count parameter
       can be specified in conjunction with the interval parameter. If the count  parameter  is  specified,  the
       value  of  count  determines  the  number of reports generated at interval seconds apart. If the interval
       parameter is specified without the count parameter, the tapestat command generates reports continuously.

REPORT

The tapestat report provides statistics for each tape drive connected to the system. The following data
are displayed:

r/s The number of reads issued expressed as the number per second averaged over the interval.

w/s The number of writes issued expressed as the number per second averaged over the interval.

kB_read/s | MB_read/s
The amount of data read expressed in kilobytes (by default or if option -k used) or megabytes (if
option -m used) per second averaged over the interval.

kB_wrtn/s | MB_wrtn/s
The amount of data written expressed in kilobytes (by default or if option -k used) or megabytes
(if option -m used) per second averaged over the interval.

%Rd Read percentage wait - The percentage of time over the interval spent waiting for read requests to
complete. The time is measured from when the request is dispatched to the SCSI mid-layer until it
signals that it completed.

%Wr Write percentage wait - The percentage of time over the interval spent waiting for write requests
to complete. The time is measured from when the request is dispatched to the SCSI mid-layer until
it signals that it completed.

%Oa Overall percentage wait - The percentage of time over the interval spent waiting for any I/O
request to complete (read, write, and other).

Rs/s The number of I/Os, expressed as the number per second averaged over the interval, where a non-
zero residual value was encountered.

Ot/s The number of I/Os, expressed as the number per second averaged over the interval, that were
included as "other". Other I/O includes ioctl calls made to the tape driver and implicit
operations performed by the tape driver such as rewind on close (for tape devices that implement
rewind on close). It does not include any I/O performed using methods outside of the tape driver
(e.g. via sg ioctls).

OPTIONS

       --human
              Print sizes in human readable format (e.g. 1.0k, 1.2M, etc.)  The units displayed with this option
              supersede any other default units (e.g.  kilobytes, sectors...) associated with the metrics.

       -k     Show the amount of data written or read in kilobytes per second instead of megabytes.  This option
              is mutually exclusive with -m.

       -m     Show the amount of data written or read in megabytes per second instead of kilobytes.  This option
              is mutually exclusive with -k.

       -t     Display  time  stamps.  The  time  stamp  format  may  depend  on  the  value of the S_TIME_FORMAT
              environment variable (see below).

       -V     Print version and exit.

       -y     Omit the initial statistic showing values since boot.

       -z     Tell tapestat to omit output for any tapes for which there  was  no  activity  during  the  sample
              period.

CONSIDERATIONS

It is possible for a percentage value (read, write, or other) to be greater than 100 percent (the
tapestat command will never show a percentage value more than 999). If rewinding a tape takes 40 seconds
where the interval time is 5 seconds the %Oa value would show as 0 in the intervals before the rewind
completed and then show as approximately 800 percent when the rewind completes.

Similar values will be observed for %Rd and %Wr if a tape drive stops reading or writing and then
restarts (that is it stopped streaming). In such a case you may see the r/s or w/s drop to zero and the
%Rd/%Wr value could be higher than 100 when reading or writing continues (depending on how long it takes
to restart writing or reading). This is only an issue if it happens a lot as it may cause tape wear and
will impact on the backup times.

For fast tape drives you may see low percentage wait times. This does not indicate an issue with the
tape drive. For a slower tape drive (e.g. an older generation DDS drive) the speed of the tape (and tape
drive) is much slower than filesystem I/O, percent wait times are likely to be higher. For faster tape
drives (e.g. LTO) the percentage wait times are likely to be lower as program writing to or reading from
tape is going to be doing a lot more filesystem I/O because of the higher throughput.

Although tape statistics are implemented in the kernel using atomic variables they cannot be read
atomically as a group. All of the statistics values are read from different files under /sys, because of
this there may be I/O completions while reading the different files for the one tape drive. This may
result in a set of statistics for a device that contain some values before an I/O completed and some
after.

This command uses rounding down as the rounding method when calculating per second statistics. If, for
example, you are using dd to copy one tape to another and running tapestat with an interval of 5 seconds
and over the interval there were 3210 writes and 3209 reads then w/s would show 642 and r/s 641 (641.8
rounded down to 641). In such a case if it was a tar archive being copied (with a 10k block size) you
would also see a difference between the kB_read/s and kB_wrtn/s of 2 (one I/O 10k in size divided by the
interval period of 5 seconds). If instead there were 3210 writes and 3211 reads both w/s and r/s would
both show 642 but you would still see a difference between the kB_read/s and kB_wrtn/s values of 2 kB/s.

This command is provided with an interval in seconds. However internally the interval is tracked per
device and can potentially have an effect on the per second statistics reported. The time each set of
statistics is captured is kept with those statistics. The difference between the current and previous
time is converted to milliseconds for use in calculations. We can look at how this can impact the
statistics reported if we use an example of a tar archive being copied between two tape drives using dd.
If both devices reported 28900 kilobytes transferred and the reading tape drive had an interval of 5001
milliseconds and the writing tape drive 5000 milliseconds that would calculate out as 5778 kB_read/s and
5780 kB_wrtn/s.

The impact of some retrieving statistics during an I/O completion, rounding down, and small differences
in the interval period on the statistics calculated should be minimal but may be non-zero.

ENVIRONMENT

       The tapestat command takes into account the following environment variables:

       S_COLORS
              By default statistics are displayed in color when the output is connected to a terminal.  Use this
              variable  to change the settings. Possible values for this variable are never, always or auto (the
              latter is equivalent to the default settings).
              Please note that the color (being red, yellow, or some other color) used to display a value is not
              indicative of any kind of issue simply because of the color. It only indicates different ranges of
              values.

       S_COLORS_SGR
              Specify the colors and other attributes used to display statistics on the terminal.  Its value  is
              a  colon-separated  list  of  capabilities  that defaults to I=32;22:N=34;1:W=35;1:X=31;1:Z=34;22.
              Supported capabilities are:

              I=     SGR (Select Graphic Rendition) substring for tape names.

              N=     SGR substring for non-zero statistics values.

              W= (or M=)
                     SGR substring for percentage values in the range from 75% to 90% (or in the  range  10%  to
                     25% depending on the metric's meaning).

              X= (or H=)
                     SGR substring for percentage values greater than or equal to 90% (or lower than or equal to
                     10% depending on the metric's meaning).

              Z=     SGR substring for zero values.

       S_TIME_FORMAT
              If this variable exists and its value is ISO then the current locale will be ignored when printing
              the  date  in  the  report  header. The tapestat command will use the ISO 8601 format (YYYY-MM-DD)
              instead.  The timestamp displayed with option -t will also be compliant with ISO 8601 format.

BUGS

       /sys filesystem must be mounted for tapestat to work. It will not work on kernels that do not have  sysfs
       support

       This  command  requires kernel version 4.2 or later (or tape statistics support backported for an earlier
       kernel version).

       Although tapestat speaks of  kilobytes  (kB),  megabytes  (MB)...,  it  actually  uses  kibibytes  (kiB),
       mebibytes (MiB)...  A kibibyte is equal to 1024 bytes, and a mebibyte is equal to 1024 kibibytes.

FILES

       /sys/class/scsi_tape/st<num>/stats/*
              Statistics files for tape devices.

       /proc/uptime contains system uptime.

AUTHOR

       Initial revision by Shane M. SEYMOUR (shane.seymour <at> hpe.com)
       Modified for sysstat by Sebastien Godard (sysstat <at> orange.fr)