SAP Note 18933 - BRBACKUP, BRARCHIVE: tape management/blocking period

Symptom:

• The backup on tape with BRARCHIVE or BRBACKUP does not start.
  The following message is output:
  
  BR105E: x free backup volume found, x required.
  

• General customer information on the topic:
  Automatic tape management and blocking periods for BRBACKUP und BRARCHIVE
  

Cause and prerequisites

The tape is "logically" or "physically" blocked.

Solution

The automatic tape management (ATM) of BRBACKUP and BRARCHIVE means the automatic cyclical allocation of tapes for a backup run from a number of tapes which is predefined in the profile or by means of a switch, taking the logical blocking period into account.

The "logical blocking period" results from the expiry period (the number of days in the profile parameter 'expir_period') and the start date of the last backup onto tape which is stored in the database table SDBAD.
While BRBACKUP always evaluates table SDBAD, BRARCHIVE does not read this table. Instead it reads the summarized log which is stored as a file
'$ORACLE_HOME/saparch/arch.log'.
This contains the same, or even more up-to-date, information since it is also accessible when the database is closed.

In addition, the observance of the "physical blocking period" is checked (outside the ATM) which also results from the parameter 'expir_period' in connection with the backup date stored in the label of the tape.
Caution: The blocking period (logical and physical) is determined only according to the date (and not according to the time). For example, if a tape for a backup has 'expir_period = 1' (that is, 1 day) and the backup is started at 23:59, the tape is released again 1 minute later (after midnight).

BRBACKUP and BRARCHIVE select tapes in the sequence specified in the profile
$ORACLE_HOME/dbs/init.sap
in the parameters 'volume_backup' or 'volume_archive' or prioritized according to the option '-v' if this is specified in the command line.
Selection from the profile parameter lists takes place cyclically, that is, the tape following the one that was last used is selected.
If option '-v' is used, selection does not take place cyclically but always starts with the first tape in the list.
Tapes for which the blocking period has not yet expired are always omitted.

The cyclical choice of tapes can be deactivated if, for a specific backup, a tape is used which does not belong to the tape pool as defined in the
init.sap
parameters volume_backup and volume_archive. This can occur if BRBACKUP/BRARCHIVE is called with the option
-v or -v SCRATCH
and a "foreign" tape is inserted. In this case the first (not the next) free tape in the pool will be chosen. For this reason, the correct tape must be indicated explicitly. The detailed BRBACK log allows you to determine the tape used last. The entries in the tape pool allow you to dermine the next tape that should be used for the backup. Start the first of the following backups explicitly for these tapes (as determined above):
brbackup/brarchive -v [,,...]
As of SAP release 3.0 the problem no longer appears.

CAUTION: In certain circumstances, differences between the tapes displayed with -q (query) and those actually requested during the later backup. This problem can occur if:

• the backup is started the next day (after midnight) or

• the tape pool was dimensioned too tightly, so that the tape pool has no tapes within the blocking period available for additional backups.

In this case, tapes which would have been selected sa the nest are still blocked duing the -q query and are thus ignored. They are released only after midnight and therefore requested by the next started backup. To avoid these situations, both actions should be started on the same day: shift the backup to before midnight, e.g., at 23:00. At the same time, the tape pool
(init..sap
parameters volume_backup and volume_archive) should be extended, so that the tapes to be used are not released just on the day of the backup.

BRBACKUP/BRARCHIVE prompt the user to insert the proper tape (as determined above) in the device. Afterward, the inserted tape is checked by ID record, name and the physical blocking period.

ATM (including the check of the logical blocking period) can be turned off:
generally with the profile parameter 'volume_backup = SCRATCH' or temporarily with the switch '-v SCRATCH.' Any tape with a physical blocking period that has expired is then accepted, that is the physical blocking period is still checked.
Caution: If 'SCRATCH' is not used on its own but within a list, for example, volume_backup = (C11B01,C11B02,SCRATCH), then it is not interpreted as a keyword for deactivating the ATM but as the name of a tape!
Caution! You should only use 'SCRATCH' in exceptional cases where the ATM is to be switched off due to a number of reasons. This should NOT be used as a permanent status since tapes with the same name (here, 'SCRATCH', the same applies in general for the same tape names) cannot be identified with SAPDBA or BRRRESTORE especially during the restoring process. Restoring would then only be possible manually!

The physical blocking period can be deactivated by setting the profile parameter 'expir_period = 0'. (This also stops the logical blocking period check within the ATM, but the cycle for tape selection according to the profile parameters volume_backup and volume_archive remains.)
Any tape which has the requested name or was initialized with 'SCRATCH' is then accepted without a blocking period check.
For safety reasons this is not recommended!
SAP recommends a minimum blocking period of 14 days!
To be exact, the check for the blocking period is not directly deactivated when you enter 0, but 'expir_period = 0' has the effect that the blocking period is always recognised as expired (except for when the system date is reset.)

If a tape for which the physical blocking period has not yet expired really has to be used, it must be initialized again using 'brbackup -i force -v '.
Since the blocking period is also logically checked (see above) as well as physically checked, even an initialized tape can be logically blocked and for this reason not requested by BRBACKUP/BRARCHIVE (or rejected if it is explicitly specified by '-v ').
If the tape really must be used even in this case, the ATM must be temporarily deactivated using '-v SCRATCH' (see above).

If a tape with the name 'SCRATCH' is initialized, then it is always accepted instead of the requested tape. The physical blocking period is still checked, but in general the tape is empty (exception: see below).
Such a tape does not keep the name 'SCRATCH' in the backup, but it is assigned the name which was requested by the ATM.
Exception: The name 'SCRATCH' is kept if the ATM has been deactivated or if the name 'SCRATCH' was explicitly requested due to its occurrence in a list (see above).