SAP Note 25592 - SAP DB (ADABAS D) and RAID

Symptom:

None

Cause and prerequisites

None

Solution

Remark: version 3.1.2 is no longer supported.

Striping:

Striping of hard disks or partitions has no advantages for SAP DB
(Adabas)
Operation of SAP DB with RAID systems:

SAP DB systems can also be operated with RAID architectures without limitations as long as the following statements are taken into consideration:

• The log should be physically separated from the data. That is, it should not depend on the same controller.
  For the log, using a DUAL mode (2 hard disks for Release 6.2, 3 hard disks for Release 6.1) is recommended.

• Mirroring is not absolutely necessary.
  If the log is to be used with RAID, it must be RAID1 (complete mirroring). The logging procedure is a sequentially based action, i.e. the write head(s) normally retain its (their) position until the next request. This advantage is destroyed by Stripe Sets or RAID5.
  As of Release 6.1.1, the DUAL LOG mode has one transaction log (1 hard disk) and one archive log reflected in the database. The NORMAL LOG mode has one transaction log and a non-reflected archive log, that would be mirrored via RAID1.
  If you choose the DUAL mode in 6.1.1, the system goes on running if a log is lost.
  The log mode SINGLE can also be used with RAID1 (3.1.2 and 6.1.1)
  

• Data can be stored in RAID5 disk arrays under observation of a few critical areas (see below) in RAID5 disk arrays. The following should be taken into account:

In Release 3.1.2, all systems up to Windows NT should be used with 2GB raw partitions. As of Release 6.1, larger partitions are possible under AIX 4.x and OSF/1.
When selecting the RAID array, you should make sure that sufficient Caches are available (Minimum 16 MB) and that the entire data IO is not concentrated on one controller. This applies especially to Release 3.1.2, in Release 6.1.1 it is no longer as relevant.
RAID5 is generally slower than other systems, especially when writing. Better values can only really be achieved with a very generous cache and controller rating.
Security aspects must be matched against performance in this case.
Due to these facts, we can only partially recommend the use of RAID5 for hard disks. The new I/O implementation in Release 6.1.1 allows RAID5 to be used ealier, although the writing performance must be observed in the high-end, as it may cause problems.

Additional key words

RAID1, mirroring, striping, among other things