Tuning Recovery - Expert Oracle RAC Performance Diagnostics and Tuning - page 329

Performance tuning strategies that apply to taking data of disk (backup) to a backup media would also apply to
taking data from backup media and reapplying it back to the disk (restore). Tuning backup would require looking at
various layers of the hardware stack. Some of the key tuning principles include the following:

1. Determine throughput: It's important to determine the maximum input disk, output media,

and network throughput. Throughput of the various devices should be determined to
understand how fast I/O could be done. For example, to test the maximum throughput of the
disk I/O subsystem, tools such as ORION can help. Network throughput will depend on the
type of configuration; for example, in a RAC environment, multiple instances could be used
to perform backup in parallel, which means interconnect would be used to some extent. If
the backup sets are being written to external media, it may be good idea to have dedicated
backup networks and when tuning the network, checking the network buffer sizes, media
management client/server buffer size, client/socket timeout parameter settings, and so forth.

2. Configure disk for optimal performance: Using ASM for storage of archive logs and backup

sets would help improve overall performance and would also improve recovery time.

3. Optimize throughput to the backup destination: To get maximum potential of the bandwidth

between the backup process and the I/O subsystem (disk or tape), utilize asynchronous I/O.

• For disk backup: On systems where native asynchronous I/O is not supported,

set DBWR_IO_SLAVES parameter to a 4 per session.
For tape backup: Set BACKUP_TAPE_IO_SLAVES parameter to 1 per channel process. •

4. Optimize Backup methods: Utilizing tools such as RMAN to backup data and restore data

would help maintain a balanced backup strategy. When using RMAN backup, optimize the
various RMAN parameters:

• Number of channels

• Parallelism

FILESPERSET parameter • Number of backup sets defined by

• Maximum size of backup set

5. Tuning RMAN: Apart from configuration parameters we discussed in the previous step,

there are a few other parameters that may help to tune the backup and restore operations:
• _BACKUP_FILE_BUFCNT
Defaults to 16, normally matches the number of disks •

• Number of input buffers per channel allocated: When the number of disks is large and

a higher number of channels need to be allocated, then this value can be increased to
improve overall performance.
Achieve balance between memory usage and I/O •

• _BACKUP_FILE_BUFSZ
Defaults to 1048576 and normally matches the stripe size of the I/O subsystem.

•

When larger stripe sizes are used when configuring ASM diskgroups, the value of this
parameter needs to be adjusted or sized to match the stripe size.