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Full Discussion: iostat output vs TPC output (array layer)
Special Forums Hardware Filesystems, Disks and Memory iostat output vs TPC output (array layer) Post 302517231 by arizah on Tuesday 26th of April 2011 08:35:38 AM
Old 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 ULTRIX

iostat

iostat(1)						      General Commands Manual							 iostat(1)

Name
       iostat - report I/O statistics

Syntax
       iostat [ -c ] [ -t ] [ disknames ] [ interval ] [ count ]

Description
       The  command  reports  I/O  statistics for terminals, disks and cpus.  For terminals the number of input and output characters are counted.
       For disks the number of 512 byte blocks per second and number of transfers per second are displayed.  For cpus, it provides the	percentage
       of  time  the system has spent in user mode, in user mode running low priority (niced) processes, in system mode, and idling.  On multipro-
       cessor systems these cpu statistics represent a cumulative summary of all the cpus.

       The optional disknames argument causes disk statistics to be displayed for the specified disks.	If this argument  is  not  specified  then
       disk statistics will be displayed for the first 3 disks only.

       The  optional interval argument causes to report once each interval seconds.  The first report is for all time since a reboot and each sub-
       sequent report is for the last interval only.

       The optional count argument restricts the number of reports.

Options
       -c   Displays the percentage of time each cpu spent in user mode, running low priority (nice'd) processes, in system mode, and idling.

       -t   Displays the number of characters read from and written to terminals.

Examples
       This example will cause cpu and disk statistics for the 5 disks ra0, ra1, ra2, ra3, and ra4.
	    iostat ra0 ra1 ra2 ra3 ra4
       This example will cause cpu, terminal, and disk statistics for ra0 to be displayed and updated every 2 seconds.
	    iostat -t ra0 2

Files
See Also
       vmstat(1), cpustat(1)

																	 iostat(1)
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