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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 302517362 by DGPickett on Tuesday 26th of April 2011 02:59:55 PM
Old 04-26-2011
Well, it is a complex world, with security and speed in opposition. One oddity of expanding sidk sizes is that one new big disk may be overwhelmed with the level of I/O that used to be handled by 8 disks, so size attracting query and churn is a negative! Striping allows the bandwidth of many drives to be applied to the combined storage, with supports more buffering with faster buffer fills, if things are sequential often enough. If everything was sequential and failure was no worry, you could stipe all together for max bandwidth, but you might do better with 2 or more virtual volumes so copying, database joining and such can be sequential on each virtual device. So, there are sometimes ways to force smart parallelism, the ability to join huge sets without seeks. However, RAM and 64 bit VM have made buffering so ample that it may dilute that sort of approach. RAID has not entirely freed us from failure worry, since with all the layers of software and hardware and vendors, it seems RAID errors often never get heard until they are 2 devices down. Rebuild time is not inconsequential, either. So, your approach should go beyond hot spots to maximizing the bandwidth of a managable number of virtual volumes. Along the way, look at the pathways and how they figure into the redundancy and striping. If a controller handles both sides of a mirror, and goes wonky . . . . If striping runs across all controllers, scsi cables, then any controller or cable bottleneck is diluted. Intellegent use of simple mirror for high churn and RAID-N for low churn is nice, too! Sometimes, this discussion can be extended down into the app, as DB2 append tables with insert never update or delete are churn free except at the end. Disk is cheap and 100% history is wise. Churn-free data might even migrate to some hierarchical read-only store like DVD arrays. Assuming control of chaos is someone else's job can be a luxury.

But, yeah, it seems like it is still good, but might not be sufficient, and an approach with sufficiency might not make it necessary.
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LEARN ABOUT NETBSD

iostat

IOSTAT(8)						    BSD System Manager's Manual 						 IOSTAT(8)

NAME

     iostat -- report I/O statistics

SYNOPSIS

     iostat [-CdDITx] [-c count] [-M core] [-N system] [-w wait] [drives]

DESCRIPTION

     iostat displays kernel I/O statistics on terminal, disk and CPU operations.  By default, iostat displays one line of statistics averaged over
     the machine's run time.  The use of -c presents successive lines averaged over the wait period.  The -I option causes iostat to print raw,
     unaveraged values.

     Only the last disk option specified (-d, -D, or -x) is used.

     The options are as follows:

     -c count	 Repeat the display count times.  Unless the -I flag is in effect, the first display is for the time since a reboot and each sub-
		 sequent report is for the time period since the last display.	If no wait interval is specified, the default is 1 second.

     -C 	 Show CPU statistics.  This is enabled by default unless the -d, -D, -T, or -x flags are used.

     -d 	 Show disk statistics.	This is the default.  Displays kilobytes per transfer, number of transfers, and megabytes transferred.
		 Use of this flag disables display of CPU and tty statistics.

     -D 	 Show alternative disk statistics.  Displays kilobytes transferred, number of transfers, and time spent in transfers.  Use of this
		 flag disables the default display.

     -I 	 Show the running total values, rather than an average.

     -M core	 Extract values associated with the name list from the specified core instead of the default ``/dev/mem''.

     -N system	 Extract the name list from the specified system instead of the default ``/netbsd''.

     -T 	 Show tty statistics.  This is enabled by default unless the -C, -d, or -D flags are used.

     -w wait	 Pause wait seconds between each display.  If no repeat count is specified, the default is infinity.

     -x 	 Show extended disk statistics.  Each disk is displayed on a line of its own with all available statistics.  This option overrides
		 all other display options, and all disks are displayed unless specific disks are provided as arguments.  Additionally, separate
		 read and write statistics are displayed.

     iostat displays its information in the following format:

     tty
	   tin	   characters read from terminals
	   tout    characters written to terminals

     disks
	   Disk operations.  The header of the field is the disk name and unit number.	If more than four disk drives are configured in the sys-
	   tem, iostat displays only the first four drives.  To force iostat to display specific drives, their names may be supplied on the com-
	   mand line.

	   KB/t    Kilobytes transferred per disk transfer
	   t/s	   transfers per second
	   MB/s    Megabytes transferred per second

	   The alternative display format, (selected with -D), presents the following values.
	   KB	   Kilobytes transferred
	   xfr	   Disk transfers
	   time    Seconds spent in disk activity

     cpu
	   us	   % of CPU time in user mode
	   ni	   % of CPU time in user mode running niced processes
	   sy	   % of CPU time in system mode
	   id	   % of CPU time in idle mode

FILES

     /netbsd   Default kernel namelist.
     /dev/mem  Default memory file.

SEE ALSO

     fstat(1), netstat(1), nfsstat(1), ps(1), systat(1), vmstat(1), pstat(8)

     The sections starting with ``Interpreting system activity'' in Installing and Operating 4.3BSD.

HISTORY

     iostat appeared in Version 6 AT&T UNIX.  The -x option was added in NetBSD 1.4.

BSD
								   March 1, 2003							       BSD
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