tapestat - Online in the Cloud

PROGRAM:

NAME

tapestat - Report tape statistics.

SYNOPSIS

tapestat [ -k | -m ] [ -t ] [ -V ] [ -y ] [ -z ] [ 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, vhen 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

-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
When this variable is set, display statistics in color on the terminal. Possible
values for this variable are never, always or auto (the latter is the default).

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
H=31;1:I=32;22:M=34;1:N=33;1:Z=33;22. Supported capabilities are:

H= SGR (Select Graphic Rendition) substring for percentage values greater than
or equal to 75%.

I= SGR substring for tape names.

M= SGR substring for percentage values in the range from 50% to 75%.

N= SGR substring for non-zero statistics values.

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.

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