Veritas-bu

Re: [Veritas-bu] RMAN to backup big empty DB

2009-03-11 14:12:11
Subject: Re: [Veritas-bu] RMAN to backup big empty DB
From: Jared Still <jkstill AT gmail DOT com>
To: VERITAS-BU AT mailman.eng.auburn DOT edu
Date: Wed, 11 Mar 2009 10:34:11 -0700
On Fri, Feb 27, 2009 at 3:26 AM, LDi <netbackup-forum AT backupcentral DOT com> wrote:

Hi,

Could someone help us determine what to expect with this situation :

- Backup server : SERVER_A
- DB server : SERVER_B (as StorageNode or MediaServer with 4 SAN Drives attached, see below)
- DB server : PA_RISC HP-UX 11.11 (HP 9000 rp7410)
- Oracle 10g R2 DB : 3,6TB
- Real amount of datas : 50GB
- RMan allocating 3 channels (SBT)
- RMan MAXSETSIZE 128G
- RMan MAXPIECESIZE 128G
- RMan FILESPERSET 32
- Drives : 3 emulated LTO3 (VTL Quantum PVX 2TB/H)

At the moment, the backup process lasts 4.5 hours (only 8 to 10GB/H throughput) !

Is it something normal, do you have any suggestions ?

There are 3 major elements to consider:

* how fast can data be read from the source system?
* how fast can data be written on the target system?
* how fast can data be transferred from source to target?

You can easily run some simple benchmarks to test each of these.

If none of those reveal a bottleneck, you need to consider some
other things obviously. :)

For instance, what is RMAN doing during all this time?

Are you looking at the IO read rate on Oracle?

If it seems very fast, then it seems likely that RMAN is scanning much
more than the 50G of data you have.

Has this source database ever held 3TB of data?

The point of this question is really "Where are the high water marks in the datafiles?"

RMAN will scan to the high water mark - it doesn't matter how much data is
actually in the database.  If the HWM has been set so high in the datafiles
by previous data that the total value of all HWMs in the files is 3TB, then
RMAN will scan 3TB of files.

Following is a script you can run to determine where the HWM is set.

Please post the results of this script back to this thread.


Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist


set linesize 200

col file_name format a50 head 'FILE NAME'
col file_size format 999,999,999,999 head 'FILE SIZE|BYTES'
col shrink_size format 999,999,999,999 head 'SHRINK TO|SIZE BYTES'
col tablespace_name format a15 head 'TABLESPACE'
col bytes_saved format 999,999,999,999 head 'BYTES SAVED'
col max_block_id format 999999999 head 'MAX BLOCK ID'

break on tablespace_name skip 1
break on report
compute sum of bytes_saved on tablespace_name
compute sum of bytes_saved on report
compute sum of file_size on tablespace_name
compute sum of file_size on report
compute sum of shrink_size on tablespace_name
compute sum of shrink_size on report

with maxext as (
   select file_id, max(block_id) max_block_id
   from dba_free_space
   group by file_id
),
shrink as (
   select
   t.tablespace_name
   , f.file_id
   , f.file_name
   , m.max_block_id
   , f.blocks * t.block_size file_size
   , case
      when ((nvl(m.max_block_id,f.blocks+1)-1) * t.block_size) >= (128*1024)
         then(nvl(m.max_block_id,f.blocks+1)-1) * t.block_size
      else
         128*1024
   end shrink_size
from maxext m
   , dba_data_files f
   , dba_tablespaces t
where m.file_id(+) = f.file_id
and t.tablespace_name = f.tablespace_name
and t.contents = 'PERMANENT'
)
select
   s.tablespace_name
   , s.file_id
   , s.max_block_id
   , s.file_name
   , s.file_size
   , s.shrink_size
   , (s.file_size - s.shrink_size) bytes_saved
from shrink s
order by tablespace_name, file_id
/



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