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Planning DatabasesLocate this document in the navigation structure

Context

Plan the most important database properties before you create a database. The following questions are particularly significant:

  • How much application data are you expecting (database size)?

  • How much database activity are you expecting (working memory size)?

  • What are your security requirements (hardware selection, system landscape)?

Procedure

  • Estimating the Database Size

    When creating a database, you create data volumes for storing the application data and log volumes for storing the transaction log entries. The database size mainly depends on the size of the data area (set of all data volumes).

    More information: Concepts of the Database Systems, How Databases Store Data and Log Entries

    Note

    You can add or delete volumes later.

    The maximum number of data volumes is determined by the MaxDataVolumes general database parameter. More information: General Database Parameters

    The larger you choose the value for the ConverterVolumeIdLayout special database parameter, the more data volumes you can use. Note that the maximum permitted size of the individual data volumes is reduced accordingly. More information: Special Database Parameters

    Description

    Calculation Formula

    Minimum Value

    Maximum Value

    Number of data volumes

    2^(ConverterVolumeIdLayout)-1

    1

    4095

    Note

    The default value of ConverterVolumeIdLayout is 8.

    With this default value, the maximum number of data volumes is 255.

    Size of a data volume

    <page_size> x(2^(32-ConverterVolumeIdLayout)-1)

    Page size = 8 KB

    1000 pages or 8000 KB

    512 GB

    Note

    The default value of ConverterVolumeIdLayout is 8.

    With this default value, the maximum size of a data volume is 128 GB.

    Size of the data area (sum of all data volumes)

    -

    1000 pages or 8000 KB

    32 TB

    Number of log volumes

    -

    1

    10,000

    Size of a log volume

    -

    -

    32 TB

    Size of the log area (sum of all log volumes)

    -

    -

    32 TB
    Recommendation

    If you create data volumes of the FILE type in SAP systems, use the following formula: Calculate the square root of the total amount of space in GB that is available for the data volumes and round up to the nearest integer.

    Example: Up to 50 GB of space is available for the data volumes. Square root (50) = 7.07, which means that 8 data volumes are recommended.

  • Choosing and Configuring Disks for the Volumes

    The speed with which the database system can read data from the volumes and write data to the volumes has a significant influence on the performance of the database.

    Since the database system logs all data changes in the log volumes, the log volumes are the areas of the database with the highest write activity.

    Recommendations:

    • Use different hard disks for the data volumes and the log volumes.

      More information: SAP Note 869267 Information published on SAP site (FAQ: MaxDB LOG area)

    • For the log volumes, do not use disks that already contain swap or paging areas.

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

    • Unix and Linux only: Do not use hard disks with journal file systems for the volumes. Journal file systems carry out their own logging of data changes, which is unnecessary for the database system and leads to performance reduction.

    • If your operating system supports the switching off of the operating system buffer cache, configure the support database parameters UseFilesystemCachingForVolume and UseFilesystemCachingForBackup accordingly.

      More information: Support Database Parameters

  • Choosing and Configuring RAID Systems

    RAID systems have several advantages, among others better performance than storage on normal disks and a potentially very large storage capacity.

    Recommendations:

    • Mirror the log area using hardware-based means, for example by using RAID-1, RAID-10, RAID-0+1 or RAID-DP systems. For security and performance reasons, do not use RAID-5 systems.

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

    • Even if you are using RAID systems for your data area, create several data volumes for the database.

      Since 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 fault-tolerant hardware, then extend it only with the same type of hardware.

      For example, extend RAID-5 systems with RAID-5 systems only.

    • When you select your RAID system, make sure that the RAID controller has a good write performance and that caches can still be backed up to disk even when there is a power outage.

  • Configuring Raw Devices

    On Unix, you can 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.

    Recommendations:

    • If you create data volumes on a raw device, do not configure them larger than the actual size of the raw device.

    • Make sure that every raw device is only accessed by one database.

    More information: SAP Note 912905 Information published on SAP site (FAQ: Storage systems used with MaxDB)

  • Choosing a Processor Architecture

    The SAP MaxDB architecture benefits greatly from the advantages of 64 bit platforms (for example, better memory management).

    We recommend that you run SAP MaxDB on a 64-bit platform.

    More information: SAP Note 1013441 Information published on SAP site (Upgrade required: Advantages for MaxDB on 64-bit platforms)

  • Choosing an Adequate Working Memory Size

    The size of the working memory that the database system uses for I/O operations (I/O buffer cache) has a big impact on the performance of your database. The larger the I/O buffer cache, the fewer time-consuming accesses to the hard discs are needed. The optimal size of the I/O buffer cache heavily depends on your application and the activity on your database.

    You configure the size of the I/O buffer cache with the database parameter CacheMemorySize.

Next Steps