PCP-IOSTAT(1)

💖 pcp-iostat — report block I/O statistics ✨

okay so bestie, this is pcp-iostat, aka pmiostat, living in section 1 of the manual (General Commands Manual). It's your little group chat for block I/O stats and it eats every single time. 🫶

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🌸 NAME 🌸

pmiostat, pcp-iostat — report block I/O statistics 💅

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✨ SYNOPSIS ✨

pcp [pcp options] iostat [-u?]  [-G method] [-P precision] [-R pattern]
[-x [dm][,t][,h][,noidle]]

no cap, that's the whole vibe. lowercase, tidy, iconic. 🎀

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🦋 DESCRIPTION 🦋

pcp-iostat reports I/O statistics for SCSI devices (that's the default, bestie) or for other devices — but only if you pass the -x option. Choose your fighter. 💅

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👑 OPTIONS 👑

so when you invoke this via the pcp(1) command, these pcp options become indirectly available: -A/--align, -a/--archive, -h/--host, -O/--origin, -S/--start, -s/--samples, -T/--finish, -t/--interval, -v/--version, -Z/--timezone and -z/--hostzone. If you want the full rundown on those, go read PCPIntro(1) — it's giving encyclopedia but in a good way. 📚

The extra command line options that are just for pcp-iostat are:

• -G method, --aggregate=method — says that stats for device names matching the regular expression you gave with the -R regex option should be aggregated according to method. Just so we're clear: this is aggregation based on matching device names, not temporal aggregation. When -G is used, the device name column is reported as method(regex), like fr — if you say -G sum -R 'sd(a|b)$', the device column will be sum(sd(a|b)$) and the summed statistics for sda and sdb get reported in the remaining columns. If -G is specified but -R is not, then the default regex is .*, i.e. it matches all device names. If method is sum then the statistics are summed — and yes that includes the %util column, which may therefore exceed 100% if more than one device name matches. 😭 If method is avg then the statistics are summed and then averaged by dividing by the number of matching device names. If method is min or max, the minimum or maximum statistics for matching devices are reported, respectively.
• -P N, --precision=N — this indicates the precision (number of decimal places) to report. The default precision N may be set to something other than the default (2). Note that the avgrq-sz and avgqu-sz fields are always reported with N+1 decimals of precision. These fields typically have values less than 1, so it's giving tiny-numbers-need-extra-glow. ✨
• -R pattern, --regex=pattern — restricts the report to device names matching a regular expression pattern. The pattern you give is searched as a perl style regular expression, and it will match any portion of a device name. e.g. '^sd[a-zA-Z]+' will match all device names starting with 'sd' followed by one or more alphabetic characters. e.g. '^sd(a|b)$' will only match 'sda' and 'sdb'. e.g. 'sda$' will match 'sda' but not 'sdab'. See also the -G option for aggregation options. 🔍
• -u, --no-interpolation — when replaying a set of archives, by default values are reported according to the requested sample interval (the -t option), not according to the actual interval recorded in the archive(s). Without this option PCP interpolates the values to be reported based on the records in the set of archives, which is particularly useful when the -t option is used to replay a set of archives with a longer sampling interval than the one the archive(s) was originally recorded with. With the -u option, uninterpolated reporting is enabled — every value is reported according to the native recording interval in the set of archives. When -u is specified, the -t option makes no sense and is incompatible, because the replay interval is always the same as the recording interval in the set of archive. In addition, -u only makes sense when replaying archives, see the -a option on PCPIntro(1), and so if -u is specified then -a must also be specified. no exceptions bestie, that's the rule. 🙈
• -V, --version — display version number and exit. simple. clean. iconic. 💅
• -x comma-separated-options — specifies a comma-separated list of one or more extended reporting options, as follows:
  • dm — report statistics for device-mapper logical devices instead of SCSI devices
  • t — prefix every line in the report with a timestamp in ctime(3) format
  • h — omit the heading, which is otherwise reported every 24 samples
  • noidle — Do not display statistics for idle devices
• -?, --help — display usage message and exit. the classic. 🫶

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🌈 REPORT 🌈

The columns in the pcp-iostat report have the following interpretation, and yes we're doing all of them, every single one, because you deserve the full picture:

• Timestamp — When the -x t option is specified, this column is the timestamp in ctime(3) format.
• Device — Specifies the scsi device name, or if -x dm is specified, the device-mapper logical device name. When -G is specified, this is replaced by the aggregation method and regular expression — see the -G and -R options above.
• rrqm/s — The number of read requests expressed as a rate per-second that were merged during the reporting interval by the I/O scheduler.
• wrqm/s — The number of write requests expressed as a rate per-second that were merged during the reporting interval by the I/O scheduler.
• r/s — The number of read requests completed by the device (after merges), expressed as a rate per second during the reporting interval.
• w/s — The number of write requests completed by the device (after merges), expressed as a rate per second during the reporting interval.
• rkB/s — The average volume of data read from the device expressed as KBytes/second during the reporting interval.
• wkB/s — The average volume of data written to the device expressed as KBytes/second during the reporting interval.
• avgrq-sz — The average I/O request size for both reads and writes to the device expressed as Kbytes during the reporting interval.
• avgqu-sz — The average queue length of read and write requests to the device during the reporting interval.
• await — The average time in milliseconds that read and write requests were queued (and serviced) to the device during the reporting interval.
• r_await — The average time in milliseconds that read requests were queued (and serviced) to the device during the reporting interval.
• w_await — The average time in milliseconds that write requests were queued (and serviced) to the device during the reporting interval.
• %util — The percentage of time during the reporting interval that the device was busy processing requests. A value of 100% indicates device saturation. saturated. fully booked. no notes. 🔥

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🧚 PCP ENVIRONMENT 🧚

Environment variables with the prefix PCP_ are used to parameterize the file and directory names used by PCP. On each installation, the file /etc/pcp.conf contains the local values for these variables. The $PCP_CONF variable may be used to specify an alternative configuration file, as described in pcp.conf(5).

For environment variables affecting PCP tools, see pmGetOptions(3). ✨

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💀 DEBUGGING OPTIONS 💀

The -D or --debug pcp option enables the output of additional diagnostics on stderr to help triage problems, although the information is sometimes cryptic and primarily intended to provide guidance for developers rather than for end-users. debug is a comma separated list of debugging options; use pmdbg(1) with the -l option to obtain a list of the available debugging options and their meaning.

ngl bestie, this one is for the devs. if it looks cryptic that's because it is. 😭

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🌟 SEE ALSO 🌟

PCPIntro(1), pcp(1), iostat2pcp(1), pmcd(1), pmchart(1), pmlogger(1), pcp.conf(5) and pcp.env(5).

go read them, they're all slay in their own way. 💜

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and that's the whole page, bestie!! 💖 this came to you courtesy of Performance Co-Pilot, the PCP crew, from the PCP-IOSTAT(1) era of the General Commands Manual — go forth and iostat, you absolute main character. periodt. 👑✨