Striping evenly distributes all new and modified pages across all the dbextents in a storage pool. We suggest that you use striping, even if you are not using Data Spaces Support.
For information on how to use striping, refer to Turning Striping On and Off.
You may choose not to use striping for a particular storage pool if it has only one dbextent, because in that case the database manager cannot distribute your data across several dbextents in the storage pool.
However, even with only one dbextent you may find a small performance improvement. The database manager still allocates space on the disk in blocks of 16 4KB-pages. By doing this it improves the probability that the pages you need are close together.
For the storage pools that will use striping, it is recommended that you assign each dbextent in the pool to a separate physical storage device. While the database manager distributes pages across dbextents, it does not recognize whether those dbextents are on the same physical device or several different ones. If you assign two dbextents to one physical storage device, performance will be degraded, because the database manager cannot retrieve pages from both dbextents in parallel.
If you plan to use striping, you should define several dbextents of the same size in each storage pool. If you have large and small dbextents mixed in the same pool, you may find that the database manager does not distribute pages evenly across them. Rather, it distributes pages across all the dbextents until the smallest one is full. It then continues to fill the larger dbextents.
For best performance, use at least four dbextents per storage pool. CP will only prefetch pages from four dbextents in a storage pool simultaneously. Any less than four means that CP does not have as many devices as possible to prefetch from in parallel. (Refer to Blocking and Prefetching for more information on prefetching.)
Striping only evenly distributes new or modified pages. It does not reallocate existing pages. To ensure that striping works with all your pages, unload all the dbspaces in your database, and reload them with striping turned on. This makes all the pages "new pages".
Logical mapping is the default and recommended type of mapping for most applications. However, applications that perform mostly updates may perform better with physical mapping.
Because you can only change the mapping parameter at startup time, you should always use logical mapping for your production applications, and consider physical for single-user-mode dataloads.
For each data space which is larger than 1024 megabytes, CP must keep two contiguous real storage pages until the database is shut down. These two pages are required for CP segment tables and must remain in real storage at all times. If you are using VMDSS with many databases or with a very large database, and have a constrained real storage environment, this will further reduce any real storage availability and increase system paging.
The only way to increase real storage availability in these situations is to reduce the number of databases using data spaces, or reduce the number of storage pools which are mapped to data spaces, or both.
For each data space which is less than or equal to 1024 megabytes, CP must keep one real storage page until the database is shut down.