04-26-2011
iostat output vs TPC output (array layer)
Hi Guys,
I've been having some arguments with my colleagues about one thing. Always my thought was that as as far as disk performance is concern by looking at the output of the iostat command (AIX) you would be able to identify if you have a hot disk and then by moving some files out that disk or by making sure that the same disk is not share at the array level by another busy application would be good enough and I think it had worked for me for quite a few years. I think according to IBM and I'm saying IBM because we use IBM storage if a disk shows more that 35% time active then it could be be a sign of a performance degradation. Then assuming that I can shift around some files then I might be able to spread the I/O across multiple disks. If so do I still need to go the array level (raid) and check the performance stats (in out case TPC) or the output of the iostat would be more than enough. Basically I would like to know if the output of the iostat is accurate enough to determine if we are suffering a I/O bottleneck or if I still need to check the statistics/performance reports at the array raid level to be sure. Thanks in advance for your comments..
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LEARN ABOUT CENTOS
iostat2pcp
IOSTAT2PCP(1) Performance Co-Pilot IOSTAT2PCP(1)
NAME
iostat2pcp - Import iostat data and create a PCP archive
SYNOPSIS
iostat2pcp [-v] [-S start] [-t interval] [-Z timezone] infile outfile
DESCRIPTION
iostat2pcp reads a text file created with iostat(1) (infile) and translates this into a Performance Co-Pilot (PCP) archive with the
basename outfile. If infile is "-" then iostat2pcp reads for standard input, allowing easy preprocessing of the iostat(1) output with
sed(1) or similar.
The resultant PCP archive may be used with all the PCP client tools to graph subsets of the data using pmchart(1), perform data reduction
and reporting, filter with the PCP inference engine pmie(1), etc.
A series of physical files will be created with the prefix outfile. These are outfile.0 (the performance data), outfile.meta (the metadata
that describes the performance data) and outfile.index (a temporal index to improve efficiency of replay operations for the archive). If
any of these files exists already, then iostat2pcp will not overwrite them and will exit with an error message.
The first output sample from iostat(1) contains a statistical summary since boot time and is ignored by iostat2pcp, so the first real data
set is the second one in the iostat(1) output.
The best results are obtained when iostat(1) was run with its own -t flag, so each output sample is prefixed with a timestamp. Even better
is -t with $S_TIME_FORMAT=ISO set in environment when iostat(1) is run, in which case the timestamp includes the timezone.
Note that if $S_TIME_FORMAT=ISO is not used with the -t option then iostat(1) may produce a timestamp controlled by LC_TIME from the locale
that is in a format iostat2pcp cannot parse. The formats for the timestamp that iostat2pcp accepts are illustrated by these examples:
2013-07-06T21:34:39+1000
(for the $S_TIME_FORMAT=ISO).
2013-07-06 21:34:39
(for some of the European formats, e.g. de_AT, de_BE, de_LU and en_DK.utf8).
06/07/13 21:34:39
(for all of the $LC_TIME settings for English locales outside North America, e.g. en_AU, en_GB, en_IE, en_NZ, en_SG and en_ZA, and all
the Spanish locales, e.g. es_ES, es_MX and es_AR).
In particular, note that some common North American $LC_TIME settings will not work with iostat2pcp (namely, en_US, POSIX and C) because
they use the MM/DD format which may be incorrectly converted with the assumed DD/MM format. This is another reason to recommend setting
$S_TIME_FORMAT=ISO.
If there are no timestamps in the input stream, iostat2pcp will try and deduce the sample interval if basic Disk data (-d option for
iostat(1)) is found. If this fails, then the -t option may be used to specify the sample interval in seconds. This option is ignored if
timestamps are found in the input stream.
The -S option may be used to specify as start time for the first real sample in infile, where start must have the format HH:MM:SS. This
option is ignored if timestamps are found in the input stream.
The -Z option may be used to specify a timezone. It must have the format +HHMM (for hours and minutes East of UTC) or -HHMM (for hours and
minutes West of UTC). Note in particular that neither the zoneinfo (aka Olson) format, e.g. Europe/Paris, nor the Posix TZ format, e.g.
EST+5 is allowed for the -Z option. This option is ignored if ISO timestamps are found in the input stream. If the timezone is not
specified and cannot be deduced, it defaults to "UTC".
Some additional diagnostic output is generated with the -v option.
iostat2pcp is a Perl script that uses the PCP::LogImport Perl wrapper around the PCP libpcp_import library, and as such could be used as an
example to develop new tools to import other types of performance data and create PCP archives.
CAVEAT
iostat2pcp requires infile to have been created by the version of iostat(1) from <http://freshmeat.net/projects/sysstat>.
iostat2pcp handles the -c (CPU), -d (Disk), -x (eXtended Disk) and -p (Partition) report formats (including their -k, -m, -z and ALL
variants), but does not accommodate the -n (Network Filesystem) report format from iostat(1); this is a demand-driven limitation rather
than a technical limitation.
SEE ALSO
Date::Format(3pm), Date::Parse(3pm), iostat(1), LOGIMPORT(3), PCP::LogImport(3pm), pmchart(1), pmie(1), pmlogger(1) and sed(1).
3.8.10 Performance Co-Pilot IOSTAT2PCP(1)