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iostat
146 Portal Server 6 2005Q1 • Deployment Planning Guide
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. Please consult Solaris System
Administration Guide.