PERFORMANCE OF RMAN INCREMENTAL LEVEL 1 BACKUP IS EXTREMELY SLOW in 12c (Doc ID 2297023.1)

Last updated on AUGUST 14, 2017

Applies to:

Oracle Database - Enterprise Edition - Version 12.1.0.1 to 12.1.0.2 [Release 12.1]
Information in this document applies to any platform.

Symptoms

The performance of RMAN incremental level 1 backup is extremely slow.
BCT has been already enabled but this symptom still appears.

First, customer make a rman incremental level 0 backup into internal ZFS Storage which is included into Supercluster in default.
Below is the information for rman incremental 0 backup

+ INPUT_BYTES_DISPLAY : 176.83T
+ OUTPUT_BYTES_DISPLAY : 176.83T
+ INPUT_BYTES_PER_SEC_DISPLAY : 3.31G
+ OUTPUT_BYTES_PER_SEC_DISPLAY: 3.31G
+ TIME_TAKEN : 15:10:51

However, when customer tried to make rman incremental level 1 backup, the performanc of rman incremental level 1 backup is quite slow like below.

+ INPUT_BYTES_DISPLAY : 113.41G
+ OUTPUT_BYTES_DISPLAY : 58.70G
+ INPUT_BYTES_PER_SEC_DISPLAY : 5.85M
+ OUTPUT_BYTES_PER_SEC_DISPLAY: 3.03M
+ TIME_TAKEN : 05:30:52

First, we suspected the performance of ZFS Storage
so we tried to make a rman rman incremental level 1 backup into REDO asmdisk
group of Exadata Storage server.
However the same symptom happened as well in Exadata Server Storage.
At that time, Disk IO usage of cell storages is 90 % ~ 100%.

So we reduced the number of rman channel from 8 to 4.
Disk IO usage of cell storages lessened to 70% ~ 80%
However, the performance of incremental level 1 backup was not improved.

Changes

 N/A

Cause

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