отчет о статистике ленты (Report tape statistics.)
Имя (Name)
tapestat - Report tape statistics.
Синопсис (Synopsis)
tapestat [ -k | -m ] [ -t ] [ -V ] [ -y ] [ -z ] [ --human ] [
interval [ count ] ]
Описание (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.
Отчет (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).
Параметры (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.
Окружение (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
H=31;1:I=32;22:M=35;1:N=34;1:Z=34;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.
Ошибки (баги) (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.
Файлы (Files)
/sys/class/scsi_tape/st<num>/stats/*
Statistics files for tape devices.
/proc/uptime contains system uptime.
