Database Reference
In-Depth Information
There is high contention on the storage subsystem due to unproportional access paths.
There is a faulty or congested I/O channel due to unproportional access paths.
There are high queue lengths due to one or more of the issues previously discussed.
To overcome any I/O-related issues, the following components would need to be examined:
Host server (number of servers)
Volume manager or storage subsystem configuration
Servers and storage subsystems should be tuned for the type of workload that would be accessing the data from
these disks.
Disk Drive Performance
Figure 12-1 illustrates the seek time vs. disk access speed. It is based on the head movement from the outside of the
disk to the inside of the disk. This shows that the speed to get a data block would be quicker from the outside than
from reading the data from the inside sectors of the disk platter. Performance of the disk drives is dictated by the
following factors:
Rotation (spindle) speed - the speed at which the disk or platters rotate, allowing the read/write
heads to retrieve or store the data. This is measured in revolutions per minute (RPM).
Seek time - the average time it takes to find the data on the platters; does not include the read time.
Speed and size of the disk buffer memory.
Seek
Figure 12-1. Seek time and seek speed 2 , 3
The access time can be illustrated as:
Access Time = Command Overhead Time + Seek Time + Settle Time + Rotational Latency
2 Oracle 10g RAC - Grid, Services, and Clustering , Murali Vallath, Digital Press, 2007.
3 Oracle Automatic Storage Management - Under-the-Hood & Practical Deployment Guide, Nitin Vengurlekar, Murali Vallath,
Rich Long, Oracle Press, 2008.
 
 
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