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DBA - Backup: Strategies

Integrated disk-to-disk backup and recovery:
- Low-cost disks used for fast recovery area
Fast incremental backups:
- Back up only changed blocks
Nightly incremental backup rolls forward recovery area backup:
- No need to do full backups

diagram_suggested_backup_strategy

tiered storage configuration:(as shown in the slide)
- used by RMAN to fully automates disk-based backup and recovery
- You can use different types of storage for the database files and the fast recovery area (FRA).
Oracle-suggested backup strategy:
- perform a full backup of your database (an image copy of each data file).
- set up automated nightly incremental backups, stored in the FRA.
  - Only changed data blocks are backed up, which save considerable storage space.
  - You can implement block change tracking to track the changed blocks more efficiently.
  - The nightly incremental backups can be used to roll forward the database backup (by applying an incremental level 1 backup) and automatically create a full backup.
    - This procedure enables faster backups by propagating changes to the FRA.
    - In addition, restores are faster because backup files are copied from the FRA or a copy of the file in the FRA. (If recovery is needed, then only the daily archived redo logs need to be applied to yesterday’s full backup.) 可以提高恢复效率,因为只适用前一日的 redo log

diagram_suggested_backup_strategy

Oracle-suggested backup strategy with Enterprise Manager
- By default, there is a 24-hour recovery window from disk.
- uses the incremental backup and incrementally updated backup features, providing faster recoverability than is possible when applying database changes from the archived log files. 比使用 archive log 的恢复快.
Enterprise Manager’s Schedule Backup function:
- The Oracle-suggested strategy takes a full database copy as the first backup.第一次备份=full&whole
  - Because it is a whole database backup, you might want to consider taking this at a period of least activity.
- An incremental backup to disk is taken every day.
- Optionally, a weekly tape backup can be made, which backs up all recovery-related files.

backup_strategies

Well suited for:
- Databases that can tolerate hours/days RTO 日级恢复时间
- Environments where disk is premium 磁盘不足
- Low-medium change frequency between backups (<20%) 备份间变化不大
Backup strategy:
- Weekly level 0 and daily differential incremental backup sets to tape,
- optional backup compression
- Enable block change tracking so that only changed block chunks are read and written during incremental backup.
- Back up archived logs and retain on-disk, as needed.

strategy_full_incremental

take advantage of RMAN support for binary compression of backup sets. 可以利用压缩,除非以下情况
- if your tape device performs its own compression, you should not use both RMAN backup set compression and the media manager vendor’s compression.
- In most cases, the media manager compression provides better results.
When you enable block change tracking, RMAN uses a block change tracking file to identify modified block chunks, and backs up only those blocks.
- Instead of scanning every block in the data file that is being backed up, RMAN reads the small bitmap file to determine which blocks have changed.

Well suited for:
- Databases that can tolerate no more than a few hours RTO 小时级恢复时间
- Environments where disk can be allocated for 1x size of database or most critical tablespaces 磁碟可用
Backup strategy:
- Initial image copy to FRA, daily incremental backups
- New on-disk copy by using incrementals to roll forward copy 磁碟拷贝
- Full backup archived to tape as needed
- Archived logs backed up and retained on-disk as needed
- Fast recovery from disk or SWITCH to use image copies

strategy_incrementally_updated_disk

Create an image copy of each data file and then apply daily level 1 incremental backups to roll forward the image copy.
- avoid the overhead of creating multiple full image copies of your data files,
- can take advantage of using image copies during a recovery operation to minimize recovery time.

Well suited for:
- Databases that require no more than several minutes of recovery time in the event of any failure 分钟级恢复时间
- Environments that can preferably allocate symmetric hardware and storage for physical standby database 镜像备用实例
- Environments with tape infrastructure that can be shared between primary and standby database sites 共享磁盘
Backup strategy:
- Full and incremental backups offloaded to physical standby database
- Fast incremental backup on standby with Active Data Guard
- Backups restored to primary or standby database
- Backups taken at each database for optimal local protection

In a Data Guard environment, you can offload incremental backups to a physical standby database.
- Incremental backups of a standby and primary database are interchangeable.
- You can apply an incremental backup of a standby database to a primary database or apply an incremental backup of a primary database to a standby database. 备份可以互换
Note: The Oracle Active Data Guard option is required for the use of block change tracking on the physical standby database. 需要使用到 ADG

Backup optimization causes RMAN to back up read-only tablespaces only when no backup exists that satisfies the retention policy.
- Because read-only tablespaces are not being written to, there is no need to continually back them up as you do read/write tablespaces.
- If you change the tablespace to read/write, back it up immediately.
You can use the SKIP READONLY option of the RMAN BACKUP command to skip read-only tablespaces or data files.
备份可以略过只读.一旦变为可读写, 则需立即备份

Exploit partitioning and read-only tablespaces:
- Older partitions that contain data that is no longer changing can be moved to read-only tablespaces.
- Back up read-only tablespaces once and then periodically depending on tape retention policy.
Divide full backup workload across multiple days. 全备份需数日
Leverage database and backup compression.压缩
Save time with tablespace-level backups.
- Back up index tablespaces less frequently than data tablespaces.
- Back up scarcely used tablespaces less frequently.
- Reduce restore time for most critical tablespaces, by grouping them together in separate backup sets.
Take incremental backup when NOLOGGING operations finish to ensure recoverability.

BACKUP DATABASE NOT BACKED UP SINCE 'SYSDATE-3' DURATION 06:00 PARTIAL
MINIMIZE TIME;

When you execute the command on the first day, a full backup begins.
- It executes for six hours.
On the next day when the command executes again, the backup starts with the last file not backed up and resumes the full backup, again in a six-hour backup window.
Over the course of a few days, the entire database will be backed up.