HP ProLiant 3000 DSS Sizing and Tuning of Oracle8 for Windows NT on Compaq Ser - Page 19

DSS Sizing and Tuning of Oracle8 for Windows NT on CompaqServers Page 17 The degree of parallelism may vary between objects. The degree of parallelism for each table should be a factor of the number of partitions in the table. Optimizing TPC-D benchmarks on Compaq ProLiant machines has shown that the average degree of parallelism per object should be 2-3 times the number of CPUs. For small objects or objects that are not accessed with an index or partitioned scans, the degree of parallelism can be set to one. Memory Memory available for parallel server processes comes from the process memory, which in turn comes from virtual memory. You will need to make sure that you have enough memory for all of your processes. The PROCESSES parameter specifies the maximum number of operating system user processes that connect to the Oracle instance and should be large enough to contain the user processes, background processes and PARALLEL_MAX_SERVERS. Your SGA should be much less than your physical memory to maximize PGA memory. You will also want to make sure that your HASH_AREA_SIZE * PARALLEL_MAX_SERVERS is much less than your available real memory (physical memory minus SGA). Availability vs. Performance Once disk space for your DSS system has been calculated, it important to determine the level of protection for your drives. Database availability, performance and cost are considerations in determining the Compaq SMART Array Controller RAID level that is used. This RAID level will directly impact the physical disk space required for your DSS system. Compaq SMART Array Controller RAID levels 0, 1 and 5 are discussed from a performance aspect in this paper. Please refer to the Compaq Database Engineering White Paper Configuring Compaq RAID Technology for Database Servers for more information regarding the Compaq SMART Array Controller RAID selection and implementation RAID-0 offers no fault tolerance for your drives. It has a 1:1 write ratio (1 physical write:1logical write) and a 1:1 read ratio (1 physical read:1 logical read). All RAID-0 data is stored in one physical location. It is the lowest cost option, as your total drives is equal to the number of logical drives required. RAID-1 offers fault tolerance via data mirroring. It has a 2:1 write ratio (2 physical writes:1logical write) and a 1:1 read ratio. Due to mirroring, all RAID-1 data is stored in two physical locations, which provides the benefit of split reads. Split reads offers a performance boost, especially when there are not many writes, because the database may read from either copy of the data. RAID-1 is the highest cost, as twice the storage is required, but also the most fault tolerant. RAID-5 offers fault tolerance via distributed data guarding. It has a 4:1 write ratio (2 physical reads + 2 physical writes: 1 logical write) and a 1:1 read ratio. All RAID-5 data is stored in one physical location, so there is no benefit from split reads. The amount of storage required is one drive (parity) for every x drives (data). Under RAID-5, there is a substantial performance penalty during writes of 20-35%, depending upon your application. Compaq SMART Array Controllers have the flexibility to use either one or a combination of the above RAID levels. Depending upon your database availability, performance and cost requirements, it may be beneficial to use RAID-1 on critical drives and RAID-0 or RAID-5 on © 1998 Compaq Computer Corporation, All Rights Reserved Doc No ECG156/0398