iostat

The iostat tool gives statistics on the disk I/O subsystem. The iostat command has many options. More information can be found in the man pages. The following typical options provide information on locating I/O bottlenecks.

Output

#iostat -xn 10
                  extended device statistics
    r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b device
    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0 fd0
    2.7   58.2   14.6 2507.0  0.0  1.4    0.0   23.0   0  52 d0
   47.3    0.0 2465.6    0.0  0.0  0.4    0.0    8.8   0  30 d1

What to Look For

• %b - Percentage of time the disk is busy (transactions in progress). Average %b values over 25 could be a bottleneck.

• %w - Percentage of time transactions are waiting for service (queue non-empty).

• asvc_t - Reports on average response time of active transactions, in milliseconds. This option is mislabeled asvc_t; it indicates the time between a user process issuing a read and the read completing. Consistent values over 30ms could indicate a bottleneck.

Considerations

Add more disks to the file system. When using a single disk file system, consider, upgrading to a hardware or software RAID is the next logical step. Hardware RAID is significantly faster than software RAID and is highly recommended. A software RAID solution would add additional CPU load to the system.

Depending on storage hardware and application behavior, there may be a better block size to use besides the ufs default of 8192k. For more information, consult the Solaris System Administration Guide.