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Oracle Performance Tuning and Optimization
Disk Arrays The layout for the DSS system on a disk array is much simpler than it is on traditional disk drives. The minimal configuration for a DSS system on a disk array should look something like this:
Both the data files and the indexes should be striped over as many disk drives as necessary to achieve optimal I/O rates on those disks. From Chapter 14, Advanced Disk I/O Concepts, remember that you can only push a disk drive to a maximum random I/O rate. Unlike traditional disk drives, when you use a disk array, the data is automatically striped across all the disk drives; therefore, it is necessary to create only one tablespace and table for all your data. You do not even have to put indexes into another tablespacealthough I recommend doing so for other reasons (such as monitoring and maintenance). With traditional disk partitioning, it is difficult to manage hundreds of data files and disks; with a disk array, you can manage hundreds of disks with just a few data files. Of course, Oracle has a 2-gigabyte limitation on the size of a data file, but this is easily resolved by creating a data file for every 2 gigabytes of space you need. The data files can all reside on the same disk array volume. By splitting tablespaces into several data files with tables striped across them, all residing on the same logical volume, you can take better advantage of the Parallel Query option. If you use a disk array, many of the management tasks and load balancing tasks are greatly simplified. With the disk array, you also have the option of using fault tolerance without affecting system performance. Of course, using fault tolerance requires significantly more disks. I recommend that you use a disk array if possible. Software striping is fine, but if your system is under heavy loads (as it is with a typical DSS system), you can achieve better performance by offloading the striping overhead to a hardware RAID controller. Hardware ConsiderationsWhen choosing hardware to use with a DSS system, consider these factors:
If you can take advantage of the Oracle Parallel Query option, many different processes will use the machine at once; an SMP or MPP machine should scale very well. Because an SMP architecture uses CPUs based on the processes that are available to be run, if you always have a runnable process available for each CPU, you should see good scaling by adding additional processors. With an MPP machine, you see a similar effect but on a much larger scale. Because there is much random access to the disks, you can benefit from a disk array. I prefer hardware striping to OS striping because hardware striping does not incur any additional overhead for the operating system and does not take up valuable CPU cycles. If hardware striping is not available, OS striping is a good alternative. Because network traffic is probably not very high, you really dont have to worry too much about segmenting the network. If you are constantly updating the DSS system from the OLTP system, however, network traffic may be more of an issue.
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