Disk Configuration (SAP Library - SAP/ MS SQL Server DBA in CCMS (BC-DB-MSS-DBA))

Disk Configuration

The following gives recommendations on how to distribute files to disks in an R/3 environment to ensure database security. You should have at least 3 disks.

Locate at least each of the following components of your system on separate disk systems:

R/3 database on a RAID5 system (or RAID0+1)
R/3 transaction logs on a RAID1 system
Other files such as the NT operating system, NT page file, tempdb database and executables on a disk or RAID system

Use hardware RAID systems and not the software mirroring offered by the NT disk manager.

Configure the system with two NT operating systems. The second, auxiliary version is used to perform backup and restore operations with the NT backup program.

Set the option NT option Automatically adjust clock for daylight saving times in the main NT system, but not in the auxiliary system.

If your system has write back caches for hard disks and RAID controllers, switch these off. Otherwise, in the event of a power failure, the data in the cache could be permanently lost resulting in a corrupted database. In systems with a standby battery buffered cache, you may leave write caches on, if the manufacturer explicitly recommends this for databases.

Disk read caches should always be turned on for maximum performance.

The following table shows a minimal disk configuration for the R/3 System running with a SQL Server Database. Note that the letters for the devices have been chosen to indicate their contents, for example, D: for R/3 data.

Optionally, if you have the disk capacity available it would benefit the throughput of your system, if you place one or more of the following system components on separate disks. The distribution of files could then look like this:

P: The NT page file

T: Files for the Tempdb

C: Files for the SQL Server, NT and R/3 executables

Example of Minimal ConfigurationTable

Folder	Disk	Files
C:\WINNT	1	NT Operating System
C:\HELPNT	1	Auxiliary NT version
C:\MSSQL7	1	SQL Server executables
C:\MSSQL7DB	1	msdb and master databases
C:\TEMPDB	1	tempdb
C:\USR\SAP	1	R/3 executables
C:\pagefile.sys	1	NT page file
D:\<SID>DATA	2	R/3 database, data files
L:\<SID>LOG	3	R/3 database log files

For the sake of clarity, this documentation refers to the disks of the example configuration as follows:

Disk 1	Executables disk	RAID1 disk system
Disk 2	R/3 data disk	RAID5 disk system
Disk 3	R/3 log disk	RAID1 disk system

See also:

Distribution of Files to Disk