Sizing Exadata - Oracle Exadata Recipes: A Problem-Solution Approach - page 132

5-9. Determining Your Fast Recovery Area and RECO Disk
Group Size Requirements
Problem
You wish to properly estimate the size of your Fast Recovery Area (FRA) for your Oracle 11gR2 databases, or perhaps
more specifically the selection you choose for “Backup method” in your Exadata configuration worksheet.

Solution
In this recipe, you will learn how to size your Fast Recovery and RECO disk storage on Exadata. Your first choice is
to determine whether you will be storing RMAN backups inside your Fast Recovery Area. Doing so will allow for the
fastest recovery duration, at the expense of reduced usable disk capacity for your data files inside your storage grid. If
you choose to store RMAN backups inside your FRA/RECO disk group, you should select “Backups internal to Oracle
Exadata Database Machine” as your backup method in your configuration spreadsheet. Doing so will allocate 60% of
your usable capacity for the RECO disk groups.
This choice is customizable; if, for example, you're moving one production database and multiple nonproduction
databases to Exadata that each run in NOARCHIVELOG mode, you can size your RECO disk group smaller than 60% of
usable capacity. We recommend sizing this portion to be 100% the size of each database running in ARCHIVELOG mode
that you wish to store RMAN backups inside your FRA.
Other database entities that you need to account for include archived red logs, flashback logs, online redo log
files, and control files. Your control files will be small in size, so we will ignore this in the calculations below. This
leaves you with the task of calculating the size required for archived redo logs, flash back logs, and redo log files.
The following script can be used to display, for a single database, the estimated size required for your FRA and RECO
structures. The script prompts for the following information and returns a percentage required; this percentage
should be used to decide what your ratio should be between DATA and RECO storage:

&backups_to_exa : Enter “Y” or “N” to decide between backing up your database to Exadata vs.
backing up externally.

•

&num_days : Enter an integer representing the number of days you wish to retain archived logs
on disk. This is decided in accordance with your organization's database backup and recovery
strategy.

•

&use_flashlog : Enter “Y” or “N” to indicate whether you plan to use flashback logging. If you
choose “Y,” the script will use the volume of archive log generation to represent the rate of
change (that is, DML volume) per interval.

•

Log in to your current database as SYSDBA and execute the script in Listing 5-21:

Listing 5-21. lst05-21-db-reco-fra.sql

SYS @ PROD> select dbgb, redogb, ArchMaxReq,
rmangb,flgb,
100*((dbgb+redogb)/(dbgb+redogb+ArchMaxReq+rmangb+flgb)) pct_for_data,
100*((ArchMaxReq+redogb+rmangb+flgb)/(dbgb+redogb+ArchMaxReq+rmangb+flgb)) pct_for_reco
from
( select db.dbgb, redo.redogb,
(arch.gbpd * &&num_days) ArchMaxReq,
(case
when upper('&&backups_to_exa') like 'Y%' then (db.dbgb + arch.gbpd)
else 0
end) rmangb,