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The optimum use of the I/O system is critical for I/O performance. THUS, it becomes beneficial to distribute the volumes evenly across the available I/O channels.

The PARALLELISM of the I/O gets affected by the number of data volumes.

Windows:

The asynchronous I/O of the operating system is used on Windows.

UNIX:

On UNIX the number of configured I/O threads determines the parallelism with which the SAP MaxDB/liveCache database transfers the I/O requests to the operating system.

o SAP MaxDB version lower than Version 7.7

The number of volumes * number of I/O threads for each volume (_IOPROCS_PER_DEV), gives the number of I/O threads.

o SAP MaxDB Version 7.7 or HIGHER

Volumes * (total of low/med/high queues for each volume), gives the number of I/O threads. But it can GET limited by the database parameter MaxIOPoolWorkers.

The number of threads gets increased by a number of threads that was configured too high. This results in reaching the limits of the operating system resources.

It is recommended to use the following formula to determine the size of SAP MaxDB data volumes: 'square root of the system size in GB, rounded up'.

Examples:

10 GB: 4 data volumes
50 GB: 8 data volumes
100 GB: 10 data volumes
200 GB: 15 data volumes
500 GB: 23 data volumes

1 TB: 32 data volumes

It is PREFERRED to have the same size for all the data volumes.

The optimum use of the I/O system is critical for I/O performance. Thus, it becomes beneficial to distribute the volumes evenly across the available I/O channels.

The parallelism of the I/O gets affected by the number of data volumes.

Windows:

The asynchronous I/O of the operating system is used on Windows.

UNIX:

On UNIX the number of configured I/O threads determines the parallelism with which the SAP MaxDB/liveCache database transfers the I/O requests to the operating system.

o SAP MaxDB version lower than Version 7.7

The number of volumes * number of I/O threads for each volume (_IOPROCS_PER_DEV), gives the number of I/O threads.

o SAP MaxDB Version 7.7 or higher

Volumes * (total of low/med/high queues for each volume), gives the number of I/O threads. But it can get limited by the database parameter MaxIOPoolWorkers.

The number of threads gets increased by a number of threads that was configured too high. This results in reaching the limits of the operating system resources.

It is recommended to use the following formula to determine the size of SAP MaxDB data volumes: 'square root of the system size in GB, rounded up'.

Examples:

10 GB: 4 data volumes
50 GB: 8 data volumes
100 GB: 10 data volumes
200 GB: 15 data volumes
500 GB: 23 data volumes

1 TB: 32 data volumes

It is preferred to have the same size for all the data volumes.

The MaxDB administrator is RESPONSIBLE for MONITORING the active DATABASE and also for the following activities:

• Backing up the dataset and the log area
• Executing consistency checks on the dataset to eliminate inconsistencies in the database that are caused by hardware defects.
• Updating the OPTIMIZER statistics (Update Statistics).
• Executing performance analyses.
• Monitoring the FREE memory.

The MaxDB administrator is responsible for monitoring the active database and also for the following activities:

No, there is no limit for the number of simultaneous sessions of an SAP MaxDB database. The database parameter MaxUserTasks is used to configure the number of database sessions that can be logged on SIMULTANEOUSLY to the database.

OLTP:

The number of database USERS in OLTP systems should be configured to at least 2 x <number_SAP processes > + 4.

BW:

The number of database users in OLTP systems should be configured to at least 3 x <number_SAP processes > + 4.

Java applications:

The maximum number of connections to the database in the connection pool is determined for each J2EE instance (NW 7.1 is the default 70). The sum of connections (connection pool) of all J2EE instances + 4 is used to calculate the number of PARALLEL user sessions (MaxDB parameter: MaxUserTasks).

liveCache:

The formula which is used to calculate the value for the database parameter MaxUserTasks for liveCaches in SCM system 4.1 and LOWER is:

2 x <number_SAP processes > + 4

The formula which is applied for liveCaches in SCM system 5.0 and above is:

3 x <number_SAP processes > + 4

One can also refer to 757914.

No, there is no limit for the number of simultaneous sessions of an SAP MaxDB database. The database parameter MaxUserTasks is used to configure the number of database sessions that can be logged on simultaneously to the database.

OLTP:

The number of database users in OLTP systems should be configured to at least 2 x <number_SAP processes > + 4.

BW:

The number of database users in OLTP systems should be configured to at least 3 x <number_SAP processes > + 4.

Java applications:

The maximum number of connections to the database in the connection pool is determined for each J2EE instance (NW 7.1 is the default 70). The sum of connections (connection pool) of all J2EE instances + 4 is used to calculate the number of parallel user sessions (MaxDB parameter: MaxUserTasks).

liveCache:

The formula which is used to calculate the value for the database parameter MaxUserTasks for liveCaches in SCM system 4.1 and lower is:

2 x <number_SAP processes > + 4

The formula which is applied for liveCaches in SCM system 5.0 and above is:

3 x <number_SAP processes > + 4

One can also refer to 757914.

One can configure a maximum of 255 data volumes in the SAP MaxDB STANDARD layout (PARAMETER: VOLUMENO_BIT_COUNT or ConverterVolumeIDLayout= 8). The maximum size of a data volume can be 128 GB. However the maximum total size of the data volumes can be 32 TB. The log area can also use a maximum of 32 TB.

One can configure a maximum of 255 data volumes in the SAP MaxDB standard layout (parameter: VOLUMENO_BIT_COUNT or ConverterVolumeIDLayout= 8). The maximum size of a data volume can be 128 GB. However the maximum total size of the data volumes can be 32 TB. The log area can also use a maximum of 32 TB.