Incremental differential vs. incremental cumulative backups

Original article address:Incremental differential vs. incremental cumulative backups

 

Problem:What is RMAN differential backups? What is the difference between it and RMAN cumulative backups? Are they the same as RMAN Incremental backup?
Answer:Differential and cumulative are two types of RMAN incremental backups. Sometimes, RMAN differential backups is called RMAN cumulative backups
However, RMAN incremental backups is sometimes called RMAN differential backups. These situations are confusing.

● Differential backup (for level 1 parents only)

Differential backup is the default backup type. The principle is to find the latest level 1 or level 0, and capture the changed data blocks from this time.
Differential backups is faster, because only a small number of changed blocks are stored, but it takes a longer time to restore

● Cumulative backup (for level 0 or Level 1 parents)

For cumulative backup and rman, all changed data blocks after the last level 0 are backed up.
Compared with differential backup and cumulative backup, the main advantage is that the recovery time is short, and the disadvantage is that the backup time is long and the disk overhead is large.

A simple comparison between the two is as follows:

● Recovery speed

Cumulative backups can overwrite the file back (Restore) Faster, because you only need to apply the log (recover) on a small number of overwritten files)

● Backup speed

Differential backups can take less time because it does not involve previous backups. However, it takes a longer time to recover

● Disk space

Cumulative backups requires more disk space because it will repeat and back up the previous backup.

In essence, selecting d or C is essentially a trade-off between disk overhead and recovery speed. Other conditions are equal, and the restoration speed has the highest priority.
This will minimize unplanned downtime. If you have enough disk and night backup time, you can choose C
However, if the disk space is insufficient and there is not enough time for backup, you can choose differential backups. Remember, this requires long-term recovery.


① Differential Incremental Backup (for level 1 parents only)

When differential backups and RMAN are used to find blocks with changes after the last level 1, if Level 1 is not found, all blocks with changes since the last level 0 are captured.

 

 

② Cumulative incremental backup (for level 0 or Level 1 parent backups)

For cumulative backups and rman, all changed blocks after level 0 or Level 1 are backed up.
Like differential backups, cumulative backups only backs up changed blocks. These blocks are all changed blocks since the last backup.

If the last backup is also a cumulative backups, the current cumulative backups only records "Change changes" and generates smaller Data Change sets.
Therefore, the recovery time is shorter than that of differential backups.