tapestat Man page

TAPESTAT(1) Linux User’s Manual TAPESTAT(1)

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 parame‐
ter, 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 mea‐
sured 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 mea‐
sured 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 inter‐
val 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 encoun‐
tered.

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 opera‐
tions 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 per‐
centage 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 approxi‐
mately 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 statis‐
tics 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 inter‐
nally 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 trans‐
ferred 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 sta‐
tistics calculated should be minimal but may be non-zero.

ENVIRONMENT
The tapestat command takes into account the following environment vari‐
ables:

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 statis‐
tics 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.

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).

FILES
/sys/class/scsi_tape/st/stats/* Statistics files for tape devices.

/proc/uptime contains system uptime.

AUTHOR

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

SEE ALSO

iostat, mpstat

http://pagesperso-orange.fr/sebastien.godard/

Linux OCTOBER 2015 TAPESTAT(1)

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