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Procedure documentation Configuring ontape  Locate the document in its SAP Library structure

Prerequisites

You need to configure ontape before you start using it for data recovery (that is, database archive, logical-log backup, and restore) with production data. Configuration information for ontape is held in the ONCONFIG file.

SAP recommends that you have at least two tape devices for use with ontape . Use one tape device for archiving the database and the other for backing up the logical-log. The use of two devices allows you to perform backups of your logical-log files during normal database operations without interfering with the archiving.

See the Informix release notes for details of the currently recommended tape device paths for your setup.

Procedure

  1. Edit the ONCONFIG file as user informix .

    2. The name of the ONCONFIG file is defined by the environment variable, either $ONCONFIG (UNIX) or %ONCONFIG% (NT). In SAP Systems, the file is called by default $INFORMIXDIR/etc/onconfig.<hostname>.<sid> (UNIX) or %INFORMIXDIR%\etc\onconfig.<hostname>.<sid> (NT).

  2. Make sure that the ONCONFIG file has entries for database archive as in the following table:

Example of ONCONFIG File Entries for Archive with UNIX

Description

Typical ONCONFIG entry

Explanation

Tape device path

TAPEDEV /dev/tape1

Use a symbolic link to the tape drive for archives (see note and caution below)

Tape block size (KB)

TAPEBLK 16

Use the maximum block size supported by your archive tape device

Tape data size (KB)

TAPESIZE 1950000

Use the maximum amount of data you want to put on the tape. See table "Tapesize Values" below.

Example

It is a good idea to use symbolic link values for TAPEDEV and LTAPEDEV to allow you to switch between multiple tape devices without changing the path name.

Suppose that /dev/tape1 is a symbolic link to /dev/rmt/0m . If the device /dev/rmt/0m breaks, you can simply attach a new device and link /dev/tape1 to the new device.

Caution

Do not use /dev/null on UNIX or nul on NT for TAPEDEV or LTAPEDEV if you want to perform a restore of your system up to the time of failure.

If you specify a null value for TAPEDEV , database archives are not performed and are therefore not available when a physical restore is required.

If you specify a null value for LTAPEDEV , the logical-log files are marked as backed up once they are full. However, the files are not actually backed up. Therefore, you cannot use transactions recorded in these logs when a logical restore is required.

To set TAPESIZE or LTAPESIZE (see next step) correctly, see the following table:

Tapesize Values

Tape length

No compression

Hardware compression
at ratio 1:1.4

DAT 60 meter

1250000

1750000

DAT 90 meter

1950000

2730000

DAT 120 meter (DDS-2)

3950000

5530000

DLT 15 GB

14950000

20930000

DLT 20 GB

19950000

27930000

The tapesize values in the final column assume a compression ratio of 1:1.4, typical for a mature database.

Recommendation

SAP recommends that you use tape device compression, as follows:
  1. Make sure that the ONCONFIG file has entries for logical-log backup as in the following table:

Example of ONCONFIG File Entries for Logical-Log Backup with UNIX

Description

Typical ONCONFIG entry

Explanation

Tape device path

LTAPEDEV /dev/tape2

Use a symbolic link to the tape drive for backups (see note and caution above)

Tape block size (KB)

LTAPEBLK 16

Use the maximum block size supported by your backup tape device

Tape data size (KB)

LTAPESIZE 1950000

Use the maximum amount of data you want to put on the tape. See table "Tapesize Values" above.

  1. Specify the high water mark for logical-log backup in the ONCONFIG file as follows:

    2. LBU_PRESERVE 1

    Set this parameter to prevent the logical logs from filling. If the logical logs all fill, you have to do an emergency backup, which is lengthy and complicated. The high water mark parameter specifies how many logical-log files the database server always preserves (that is, it avoids writing logging data to these files).

    With this setting, when the second to last logical-log file has filled up, the database server stops processing. This allows you to back up the full logical-log files in the normal way to allow processing to continue. Therefore, no emergency backup is necessary.

    If you have not set this parameter and all the logical-log files are full, see Performing Emergency Logical-Log Backup (ontape).

  2. To activate the parameter changes to the ONCONFIG file, shut down the SAP System and restart the Informix database server.

 

See also:

Approach to Archive (ontape)

Requirements for an Archive (ontape)

Creation of an Archive (ontape)

Approach to Logical-Log Backup (ontape)

Requirements for a Logical-Log Backup (ontape)

Creation of a Logical-Log Backup (ontape)

Full-System Cold Restore (ontape)

Partial-System Warm Restore (ontape)

Configuration of ON-Archive

Configuring ON-Bar