RMAN Restore Performance from Tape is Very Poor (Doc ID 850988.1)
RMAN Restore Performance from Tape is Very Poor (Doc ID 850988.1)
In this Document
Applies to:Oracle Server - Enterprise Edition - Version 10.2.0.4 to 11.1.0.7 [Release 10.2 to 11.1]Information in this document applies to any platform. ***Checked for relevance on 28-Jun-2011*** Symptoms
RMAN restore from sbt backup is very slow compared to backup speed. Cause
RMAN is using a 128Kb buffer size for the datafiles when restoring back to disk. To confirm that you are hitting the same problem, query v$backup_async IO and check buffer_size for the backup eg
SQL>select device_type, type, buffer_size from v$backup_async_io where
open_time > to_date('30-jun-09 15:14:00', 'dd-mon-rr hh24:mi:ss') and close_time < to_date('30-jun-09 16:14:00', 'dd-mon-rr hh24:mi:ss') ;
DEVICE_TYPE TYPE BUFFER_SIZE Buffer size used for read from disk is 1Mb. Then query the restore:
SQL> select device_type, type, buffer_size from v$backup_async_io where
open_time > to_date('30-jun-09 14:50:00', 'dd-mon-rr hh24:mi:ss') and close_time < to_date('30-jun-09 14:52:00', 'dd-mon-rr hh24:mi:ss') ;
Buffer size used for write back to disk is 128Kb SolutionChange the buffer size by setting the following hidden parameter:
SQL>alter system set "_BACKUP_KSFQ_BUFSZ"=1048576;
Users restoring to ASM may want to set this to the ASM stripe size.
Problem can affect any release prior to 11.2. Please note: Setting _BACKUP_KSFQ_BUFSZ=1048576 will benefit restore performance overall where you can see that a buffer size of 128Kb is being used. However, if restore validate is also taking a long time then setting this hidden parameter alone may not be enough, particularly if you have hardware multiplexed the original backup (allocated > 1 channel per physical tape device). If this is the case then refer to Note 740911.1: RMAN Restore Performance.
ReferencesBUG:8369094 - INCORRECT BUFFER SIZE AND ALIGNMENT FOR RMAN BACKUPSNOTE:740911.1 - RMAN Restore Performance |
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