VERITAS Storage Foundation 4.1 Oracle Administrator's Guide
Tuning VxFS Prerelease 8 September 2005, 8:55am
412 VERITAS Storage Foundation for Oracle Administrator’s Guide
â—† Average time spent on read and write operations
The following is an example of odmstat output:
# /opt/VRTS/bin/odmstat -i 5 /mnt/odmfile*
OPERATIONS FILE BLOCKS AVG TIME(ms)
FILE NAME READ WRITE READ WRITE READ WRITE
Mon May 11 16:21:10 2015
/db/cust.dbf 0 0 0 0 0.0 0.0
/db/system.dbf 0 0 0 0 0.0 0.0
Mon May 11 16:21:15 2015
/db/cust.dbf 371 0 371 0 0.2 0.0
/db/system.dbf 0 371 0 371 0.0 5.7
Mon May 11 16:21:20 2015
/db/cust.dbf 813 0 813 0 0.3 0.0
/db/system.dbf 0 813 0 813 0.0 5.5
Mon May 11 16:21:25 2015
/db/cust.dbf 816 0 816 0 0.3 0.0
/db/system.dbf 0 816 0 816 0.0 5.3
Mon May 11 16:21:30 2015
/db/cust.dbf 0 0 0 0 0.0 0.0
/db/system.dbf 0 0 0 0 0.0 0.0
Interpreting I/O Statistics
When running your database through the file system, the read-write lock on each file allows only
one active write per file. When you look at the disk statistics using iostat, the disk reports
queueing time and service time. The service time is the time that I/O spends on the disk, and the
queueing time is how long it waits for all of the other I/Os ahead of it. At the volume level or the
file system level, there is no queueing, so vxstat and qiostat do not show queueing time.
For example, if you send 100 I/Os at the same time and each takes 10 milliseconds, the disk reports
an average of 10 milliseconds of service and 490 milliseconds of queueing time. The vxstat,
odmstat, and qiostat report an average of 500 milliseconds service time.