## Planning the Database Instance

Plan the configuration before you create a database instance. Answer especially the following questions:

● How much application data do you expect (database size)?

● What hardware is suitable for your database instance?

● Do you require Unicode support?

You can change most settings that you select when you create the database instance at a later date.

#### General Notes

● If you are operating several database instances, then create each database instance on a separate computer.

#### Database Size and Configuration of Volumes

When you create a database instance, you create data volumes where the database system stores the application data. The size of the database instance is mainly determined by the size of the data area (set of all data volumes), see Data Storage.

You can add or delete volumes later.

The speed with which the database system can read data from the volumes and write data to the volumes has a significant influence over the performance of the database instance. To achieve good I/O performance when you later operate the database instance, use the following recommendations when you create and configure a new database instance.

● Note the rules on size and amount of volumes, see Technical Restrictions.

● For SAP systems we recommend configuring file type data volumes according to the following calculation formula: calculate the square root of the size available for data volumes in GB, and round up to a whole number.

SAP customers can find more information under SAP Note 820824.

Up to 50 GB are available for data volumes.

√50=7,07, which means that 8 data volumes are recommended.

● Use different disks for data volumes and for log volumes. As the database system logs all data changes in the log volumes, the log volumes are the areas of the database instance with the highest write activity.

● For swap and paging areas, use different disks than for the log volumes.

● Mirror the log area and the data area using hardware-based means, for example by using RAID-5 or RAID-1 systems. When you select the RAID system, note that the RAID Controller has a good write performance and that caches can still be saved to disk even when there is a power outage.

● Even if you are using RAID-5 systems, create several data volumes for the database instance. Because some of the database system’s parallelization techniques depend on the number of data volumes, you can improve performance if you use several data volumes instead of one data volume.

● If you are using several disks for the volumes, use disks with standardized performance data, in particular standardized access speeds. This is the only way to ensure that the disks are filled evenly.

● If you are using fault-tolerant hardware, then expand the capacity only using the same type of hardware. For example, expand RAID-5 systems with RAID-5 systems only.

● Do not create log volumes on RAID-5 systems, but only on dedicated disks or on RAID-1 systems.

● On UNIX systems, use raw devices for data and log volumes. In general the database can access raw devices quicker than files. The operating system can also start raw devices more quickly because it does not need to check the consistency of the file system.

Consider the following notes:

○ Do not configure raw device type data volumes larger than the actual size of the raw device.

○ If your operating system supports the switching off of its own buffer cache, configure the support database parameter USE_OPEN_DIRECT accordingly. See Support Database Parameter

○ Make sure only one database instance accesses one raw device.

● Only for UNIX/Linux: do not use hard disks with a journal file system for the volumes. Journal file systems perform their own logging of data changes, which is unnecessary for the database system and leads to performance reduction.

● Choose suitable settings for logging transactions, see Log Settings.

○ If hardware-based mirroring of the log area is not possible, then configure the log mode so that the database system mirrors the log area.

○ Switch off the overwrite mode for the log area.

○ Always leave the redo log management switched on.

#### Unicode Support

You can use Unicode for the database catalog and for application data in a MaxDB database instance. See Glossary, Unicode.

You cannot change the Unicode support of the database catalog later on.

See also:

Creating and Configuring a Database Instance

Database Design

Administration