Difference Between RMAN Incremental and Full Backups - Driving me Nuts!

  • From: "David Barbour" <david.barbour1@xxxxxxxxx>
  • To: oracle-l <oracle-l@xxxxxxxxxxxxx>
  • Date: Thu, 17 Jul 2008 10:20:54 -0400

Well, nuttier anyway.  Oracle 9.2.0.7 on AIX5.3L.  IBM DS4800 SAN with CIO
mounted RAID5 Oracle Datafile filesystems.  init.ora filesystems_io
parameter can be "ASYNCH" or "SETALL" - it doesn't make a difference.
TSM5.5 for tape backup. So here's what happens -

RMAN parameters - maxopenfiles=1, maxsetsize=250G, device type sbt_tape
parallelism=2 (there are 5 drives).

Full backup:  System runs 'normally' (whatever that means), people can work,
jobs complete within expected time limits, etc.  Statspack snapshot covering
period when backup is running shows top 5 timed events as follows:

Top 5 Timed Events
~~~~~~~~~~~~~~~~~~                                                     %
Total
Event                                               Waits    Time (s) Ela
Time
-------------------------------------------- ------------ -----------
--------
sbtwrite2                                      20,616,329      46,382
62.39
CPU time                                                        9,302
12.51
db file sequential read                         1,086,174       9,296
12.51
async disk IO                                  10,541,867       7,678
10.33
db file scattered read                            145,084       1,282
1.72
          -------------------------------------------------------------

Incremental backup (Level 1):  System slows to a crawl.  People complain.
Jobs take hours longer than expected (it's like they don't even start until
the backup completes).  Statspack snapshot covering period when backup is
running shows top 5 timed events as follows:

Top 5 Timed Events
~~~~~~~~~~~~~~~~~~                                                     %
Total
Event                                               Waits    Time (s) Ela
Time
-------------------------------------------- ------------ -----------
--------
async disk IO                                   9,805,203      45,977
59.34
db file sequential read                         2,401,975      23,764
30.67
db file scattered read                            130,897       3,458
4.46
CPU time                                                        2,790
3.60
sbtwrite2                                         314,812         895
1.15
          -------------------------------------------------------------

Didn't have this problem when we were using plain old jfs2 filesystems
mounted without cio.

What is the difference between disk access for the two types of backups?

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