Input Output statistics ( iostat )
iostat reports terminal and disk I/O activity and CPU utilization. The first line of output is for the time period since boot & each subsequent line is for the prior interval . Kernel maintains a number of counters to keep track of the values.
iostat’s activity class options default to tdc (terminal, disk, and CPU). If any other option/s are specified, this default is completely overridden i.e. iostat -d will report only statistics about the disks.
iostat <options> interval count
option – let you specify the device for which information is needed like disk , cpu or terminal. (-d , -c , -t or -tdc ) . x options gives the extended statistics .
interval - is time period in seconds between two samples . iostat 4 will give data at each 4 seconds interval.
count – is the number of times the data is needed . iostat 4 5 will give data at 4 seconds interval 5 times
$ iostat -xtc 5 2
extended disk statistics tty cpu
disk r/s w/s Kr/s Kw/s wait actv svc_t %w %b tin tout us sy wt id
sd0 2.6 3.0 20.7 22.7 0.1 0.2 59.2 6 19 0 84 3 85 11 0
sd1 4.2 1.0 33.5 8.0 0.0 0.2 47.2 2 23
sd2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd3 10.2 1.6 51.4 12.8 0.1 0.3 31.2 3 31
[oracle@]$ iostat -dn 5 | grep data
Device: rBlk_nor/s wBlk_nor/s rBlk_dir/s wBlk_dir/s rBlk_svr/s wBlk_svr/s
netapp:/vol/test_data 0.02 0.15 0.00 0.00 5985.39 1694.18
netapp:/vol/test_c_data 0.00 0.00 0.00 0.00 3975.35 2160.74
netapp:/vol/streams_data 0.05 0.43 0.00 0.00 230.63 45.43
netapp:/vol/test_data 0.00 0.00 0.00 0.00 70004.41 59.32
netapp:/vol/test_c_data 0.00 0.00 0.00 0.00 160.32 102.61
netapp:/vol/streams_data 0.00 0.00 0.00 0.00 12710.22 20754.31
The fields have the following meanings:
disk name of the disk
r/s reads per second
w/s writes per second
Kr/s kilobytes read per second
Kw/s kilobytes written per second
wait average number of transactions waiting for service (Q length)
actv average number of transactions actively being serviced (removed from the queue but not yet
completed)
%w percent of time there are transactions waiting for service (queue non-empty)
%b percent of time the disk is busy (transactions in progress)
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