VERITAS Storage Foundation 4.1 Oracle Administrator's Guide

Tuning VxFS Prerelease 8 September 2005, 8:55am
410 VERITAS Storage Foundation for Oracle Administrator’s Guide
If an application is doing sequential I/O to large files, it should issue requests larger than the
discovered_direct_iosz. This causes the I/O requests to be performed as discovered direct
I/O requests, which are unbuffered like direct I/O but do not require synchronous inode updates
when extending the file. If the file is too large to fit in the cache, then using unbuffered I/O avoids
throwing useful data out of the cache and lessons CPU overhead.
Obtaining File I/O Statistics using the Quick I/O Interface
The qiostat command provides access to activity information on Quick I/O files on VxFS file
systems. The command reports statistics on the activity levels of files from the time the files are
first opened using their Quick I/O interface. The accumulated qiostat statistics are reset once
the last open reference to the Quick I/O file is closed.
The qiostat command displays the following I/O statistics:
◆ Number of read and write operations
◆ Number of data blocks (sectors) transferred
◆ Average time spent on read and write operations
When Cached Quick I/O is used, qiostat also displays the caching statistics when the -l (the
long format) option is selected.
The following is an example of qiostat output:
OPERATIONS FILE BLOCKS AVG TIME(ms)
FILENAME READ WRITE READ WRITE READ WRITE
/db01/file1 0 0 0 0 0.0 0.0
/db01/file2 0 0 0 0 0.0 0.0
/db01/file3 73017 181735 718528 1114227 26.8 27.9
/db01/file4 13197 20252 105569 162009 25.8 397.0
/db01/file5 0 0 0 0 0.0 0.0
For detailed information on available options, see the qiostat(1M) manual page.
Using I/O Statistics Data
Once you gather the file I/O performance data, you can use it to adjust the system configuration to
make the most efficient use of system resources. There are three primary statistics to consider:
◆ file I/O activity
◆ volume I/O activity
◆ raw disk I/O activity