1TAPESTAT(1)                   Linux User's Manual                  TAPESTAT(1)
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NAME

6       tapestat - Report tape statistics.
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SYNOPSIS

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

12       The tapestat command is used for monitoring the activity of tape drives
13       connected to a system.
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15       The first report generated by the tapestat command provides  statistics
16       concerning  the  time since the system was booted, unless the -y option
17       is used, when this first report is  omitted.   Each  subsequent  report
18       covers the time since the previous report.
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20       The  interval parameter specifies the amount of time in seconds between
21       each report.  The count parameter can be specified in conjunction  with
22       the  interval parameter. If the count parameter is specified, the value
23       of count determines the number of reports generated at interval seconds
24       apart. If the interval parameter is specified without the count parame‐
25       ter, the tapestat command generates reports continuously.
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27

REPORT

29       The tapestat report provides statistics for each tape  drive  connected
30       to the system.  The following data are displayed:
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32       r/s
33              The  number  of  reads issued expressed as the number per second
34              averaged over the interval.
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36       w/s
37              The number of writes issued expressed as the number  per  second
38              averaged over the interval.
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40       kB_read/s | MB_read/s
41              The amount of data read expressed in kilobytes (by default or if
42              option -k used) or megabytes (if  option  -m  used)  per  second
43              averaged over the interval.
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45       kB_wrtn/s | MB_wrtn/s
46              The amount of data written expressed in kilobytes (by default or
47              if option -k used) or megabytes (if option -m used)  per  second
48              averaged over the interval.
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50       %Rd
51              Read  percentage wait - The percentage of time over the interval
52              spent waiting for read requests to complete.  The time  is  mea‐
53              sured  from when the request is dispatched to the SCSI mid-layer
54              until it signals that it completed.
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56       %Wr
57              Write percentage wait - The percentage of time over the interval
58              spent  waiting  for write requests to complete. The time is mea‐
59              sured from when the request is dispatched to the SCSI  mid-layer
60              until it signals that it completed.
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62       %Oa
63              Overall percentage wait - The percentage of time over the inter‐
64              val spent waiting for any I/O request to complete (read,  write,
65              and other).
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67       Rs/s
68              The  number of I/Os, expressed as the number per second averaged
69              over the interval, where a non-zero residual value  was  encoun‐
70              tered.
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72       Ot/s
73              The  number of I/Os, expressed as the number per second averaged
74              over the interval, that were  included  as  "other".  Other  I/O
75              includes ioctl calls made to the tape driver and implicit opera‐
76              tions performed by the tape driver such as rewind on close  (for
77              tape  devices  that  implement  rewind  on  close).  It does not
78              include any I/O performed using  methods  outside  of  the  tape
79              driver (e.g. via sg ioctls).
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OPTIONS

82       -k     Show  the amount of data written or read in kilobytes per second
83              instead of megabytes.  This option is  mutually  exclusive  with
84              -m.
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86       -m     Show  the amount of data written or read in megabytes per second
87              instead of kilobytes.  This option is  mutually  exclusive  with
88              -k.
89
90       -t     Display  time  stamps.  The  time stamp format may depend on the
91              value of the S_TIME_FORMAT environment variable (see below).
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93       -V     Print version and exit.
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95       -y     Omit the initial statistic showing values since boot.
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97       -z     Tell tapestat to omit output for any tapes for which  there  was
98              no activity during the sample period.
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CONSIDERATIONS

102       It  is  possible  for  a percentage value (read, write, or other) to be
103       greater than 100 percent (the tapestat command will never show  a  per‐
104       centage  value  more  than  999).  If rewinding a tape takes 40 seconds
105       where the interval time is 5 seconds the %Oa value would show as  0  in
106       the  intervals  before  the  rewind completed and then show as approxi‐
107       mately 800 percent when the rewind completes.
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109       Similar values will be observed for %Rd and %Wr if a tape  drive  stops
110       reading or writing and then restarts (that is it stopped streaming). In
111       such a case you may see the r/s or w/s drop to  zero  and  the  %Rd/%Wr
112       value  could  be  higher  than  100  when  reading or writing continues
113       (depending on how long it takes to restart writing or  reading).   This
114       is only an issue if it happens a lot as it may cause tape wear and will
115       impact on the backup times.
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117       For fast tape drives you may see low percentage wait times.  This  does
118       not  indicate  an  issue  with  the tape drive. For a slower tape drive
119       (e.g. an older generation DDS drive) the speed of the  tape  (and  tape
120       drive)  is  much  slower  than  filesystem  I/O, percent wait times are
121       likely to be higher. For faster tape drives (e.g. LTO)  the  percentage
122       wait times are likely to be lower as program writing to or reading from
123       tape is going to be doing a lot more  filesystem  I/O  because  of  the
124       higher throughput.
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126       Although  tape  statistics  are  implemented in the kernel using atomic
127       variables they cannot be read atomically as a group. All of the statis‐
128       tics  values  are read from different files under /sys, because of this
129       there may be I/O completions while reading the different files for  the
130       one  tape  drive.  This  may result in a set of statistics for a device
131       that contain some values before an I/O completed and some after.
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133       This command uses rounding down as the rounding method when calculating
134       per  second  statistics.  If, for example, you are using dd to copy one
135       tape to another and running tapestat with an interval of 5 seconds  and
136       over  the interval there were 3210 writes and 3209 reads then w/s would
137       show 642 and r/s 641 (641.8 rounded down to 641). In such a case if  it
138       was  a  tar archive being copied (with a 10k block size) you would also
139       see a difference between the kB_read/s and kB_wrtn/s of 2 (one I/O  10k
140       in  size divided by the interval period of 5 seconds). If instead there
141       were 3210 writes and 3211 reads both w/s and r/s would  both  show  642
142       but  you  would  still  see  a  difference  between  the  kB_read/s and
143       kB_wrtn/s values of 2 kB/s.
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145       This command is provided with an interval in  seconds.  However  inter‐
146       nally  the  interval  is tracked per device and can potentially have an
147       effect on the per second statistics reported.  The  time  each  set  of
148       statistics  is  captured  is kept with those statistics. The difference
149       between the current and previous time is converted to milliseconds  for
150       use in calculations.  We can look at how this can impact the statistics
151       reported if we use an example of a tar archive being copied between two
152       tape  drives  using dd. If both devices reported 28900 kilobytes trans‐
153       ferred and the reading tape drive had an interval of 5001  milliseconds
154       and  the  writing tape drive 5000 milliseconds that would calculate out
155       as 5778 kB_read/s and 5780 kB_wrtn/s.
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157       The impact of some retrieving  statistics  during  an  I/O  completion,
158       rounding down, and small differences in the interval period on the sta‐
159       tistics calculated should be minimal but may be non-zero.
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ENVIRONMENT

162       The tapestat command takes into account the following environment vari‐
163       able:
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166       S_TIME_FORMAT
167              If  this  variable  exists and its value is ISO then the current
168              locale will be ignored when printing  the  date  in  the  report
169              header. The tapestat command will use the ISO 8601 format (YYYY-
170              MM-DD) instead.  The timestamp displayed  with  option  -t  will
171              also be compliant with ISO 8601 format.
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BUGS

175       /sys  filesystem must be mounted for tapestat to work. It will not work
176       on kernels that do not have sysfs support
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178       This command requires kernel version 4.2 or later (or  tape  statistics
179       support backported for an earlier kernel version).
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FILES

183       /sys/class/scsi_tape/st<num>/stats/* Statistics files for tape devices.
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185       /proc/uptime contains system uptime.
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AUTHOR

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

192       iostat(1), mpstat(1)
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194       http://pagesperso-orange.fr/sebastien.godard/
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198Linux                             MARCH 2016                       TAPESTAT(1)
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