iostat
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
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| extended device | statistics |
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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
•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. Please consult Solaris System Administration Guide.
