This section describes what In-file delta technology is and how it can be used to reduce size of backup
Enable delta merging
[Delta Merging (Enable delta merging)] defines whether to enable the delta merge feature for the corresponding backup set.
To enable the delta merging feature, select the [In-File Delta] tab in the [Backup Setting] menu, and select the checkbox beside [Enable delta merging].
The delta merge feature combines the full and delta files (differential or incremental) into a single full file.
The advantage of using delta merge is it will speed up the restore of files. As a single 'merged' file can be restored faster than a file consisting of full plus related incremental files, which may require a lengthy merging process after restoring to a client machine.
Delta merge can be applied to full and differential or incremental delta files which reside in the data area. The criteria for file merging are governed by the retention policy setting for the backup set.
The following is some simple examples to demonstrate the functionality of the delta merge feature:
Example 1:
The example below shows how delta files are merged into full file using a retention policy (delta merge policy) setting defined as 4 jobs for this backup set.
A full backup file is stored into data area (F) uploaded by Job 1, followed by incremental delta files I1, I2, I3, and I4.
On the completion Job 5 (I4), the backup application will trigger a delta merge background job to execute the file merging.
When the OBS delta merge job runs F + I1 will be merged to become a merged full file.
The data area now contains 4 snapshots including merged full file after file merging.
Retention Policy = 4 Jobs (Delta Merge Policy)
Job 1 = F
Job 2 = I1
Job 3 = I2
Job 4 = I3
Job 5 = I4 (delta merge initiated)
After job 5 the backup application will initiate a delta merge for Job 1 & Job 2 files.
F (F + I1) merged full file
I2
I3
I4
Example 2:
The example below shows how delta files are merged into full file using a retention policy (delta merge policy) setting defined as 7 days for this backup set.
A full backup file is stored into data area (F) uploaded on Day 1, followed by incremental delta files I1, I2, I3, I4, I5, I6, I7, and I8.
On the completion of the backup job on Day 9 (I8), the backup application will trigger a delta merge background job to execute the file merging.
When the offsite storage server delta merge job runs F + I1 will be merged to become a merged full file.
The data area now contains 8 snapshots including merged full file after file merging.
Retention Policy = 7 Days (Delta Merge Policy):
Day 1 = F
Day 2 = I1
Day 3 = I2
Day 4 = I3
Day 5 = I4
Day 6 = I5
Day 7 = I6
Day 8 = I7
Day 9 = I8 (delta merge initiated)
After job on day 9 the backup application will initiate a delta merge for Day 1 & Day 2 files.
As the incremental file I1 has exceeded the 7 day retention policy setting.
F (F + I1) merged full file
I2
I3
I4
I5
I6
I7
I8
Example 3:
This example below shows what happens when there are multiple backup jobs occurring which generates incremental delta files within a 24 hour period.
A full backup file is stored into data area (F) uploaded by Job 1, followed by incremental delta files I1, I2, I3, and I4.
On the completion Job 5 (I4), the backup application will trigger a delta merge background job to execute the file merging.
When the OBS delta merge job runs F + I1 will be merged to become a merged full file.
Retention Policy = 4 Jobs (Delta Merge Policy)
Job 1 = F
Job 2 = I1
Job 3 = I2
Job 4 = I3
Job 5 = I4 (delta merge initiated)
Job 6 = I5
Job 7 = I6
After job 5 the backup application will initiate a delta merge for Job 1 & Job 2 files.
If after the delta merge there are further incremental uploads, e.g. Job 6 and Job 7.
These increment files will not be merged by the offsite storage server as a delta merge jobs has already taken place within the last 24 hours.
The data area now contains 6 jobs, which exceeds the delta merge policy of 4 jobs
F (F + I1) merged full file
I2
I3
I4
I5
I6
The offsite storage server will merge the extra incremental files, when the next backup job completes 24 hours after the last delta merge.
The offsite storage server will merge all the delta files which have exceeded the backup set delta merge policy.
Example 4:
The example below shows how differential and incremental delta files are merged into full file using a retention policy (delta merge policy)
setting defined as 4 jobs for this backup set.
A full backup file is stored into data area (F) uploaded by Job 1, followed by incremental and differential delta files I1, I, I3 and D1.
Retention Policy = 4 Jobs (Delta Merge Policy)
Job 1 = F
Job 2 = I1
Job 3 = I2
Job 4 = I3
Job 5 = D1 (delta merge initiated)
After Job 5 the backup application will initiate a delta merge for Job 1 & Job 2.
Unfortunately, differential delta D1 is found in delta chain, this creates delta merge stoppage, the files in Job 1 and Job 2 will not be merged.
The backup job continues with subsequent incremental backups (I4, I5 and I6).
Job 1 = F
Job 2 = I1
Job 3 = I2
Job 4 = I3
Job 5 = D1 (delta merge is initiated and stopped)
Job 6 = I4 (delta merge is initiated and stopped)
Job 7 = I5 (delta merge is initiated and stopped)
Job 8 = I6 (delta merge is initiated)
After Job 8 the backup application will initiate a delta merge, the offsite storage server will merge the full file (F) uploaded in Job 1 with the differential delta D1 uploaded in Job 5 to form the new full file (As the D1 differential includes changes in I1 + I2 + I3).
The incremental files I1 + I2 + I3 will be moved to the retention area, as they have already exceeded the retention policy of 4 jobs.
These files will be purged on the next retention policy job.
After the delta merge has completed the follow files will be available for restore.
F (F + D1)
I4
I5
I6
Example 5:
The example below shows how delta merge handles multiple differential delta files using a retention policy (delta merge policy) setting defined as 4 jobs for this backup set.
A full backup file is stored into data area (F) uploaded by Job 1, followed by incremental and differential delta files I1, I2, I3 and D1.
Retention Policy = 4 Jobs (Delta Merge Policy)
Job 1 = F
Job 2 = I1
Job 3 = I2
Job 4 = I3
Job 5 = D1 (delta merge initiated)
After Job 5 the backup application will initiate a delta merge for Job 1 & Job 2.
Unfortunately, differential delta D1 is found in delta chain, this creates delta merge stoppage, the files in Job 1 and Job 2 will not be merged.
The backup job continues with subsequent differential delta backups (D2 and D3) and incremental delta backups (I4, I5, and I6).
Job 1 = F
Job 2 = I1
Job 3 = I2
Job 4 = I3
Job 5 = D1 (delta merge is initiated and stopped)
Job 6 = D2 (delta merge is initiated and stopped)
Job 7 = D3 (delta merge is initiated and stopped)
Job 8 = I4 (delta merge is initiated and stopped)
Job 9 = I5 (delta merge is initiated and stopped)
Job 10 = I6 (delta merge is initiated)
After Job 10 the backup application will initiate a delta merge, the offsite storage server will merge the full file (F) uploaded in Job 1 with the latest differential delta D3 uploaded in
Job 7 to form the new full file (As the D3 differential includes changes in I1 + I2 + I3 + D1 + D2).
The files I1 + I2 + I3 + D1 + D2 will be moved to the retention area, as they have already exceeded the retention policy of 4 jobs.
These files will be purged on the next retention policy job.
After the delta merge has completed the follow files will be available for restore.
F (F + D3)
I4
I5
I6
Example 6:
The example below shows how delta merge handles multiple differential delta files with different compression type.
A full backup file is stored into data area (F) uploaded by Job 1, followed by incremental and differential delta files I1 and I2.
Retention Policy = 3 Jobs (Delta Merge Policy)
Job 1 = F (Fast Compression)
Job 2 = I1 (Normal Compression)
Job 3 = I2 (No Compression)
Job 4 = I3 (Fast Compression, delta merge initiated)
After Job 4 the backup application will initiate a delta merge for Job 1 & Job 2.
When F merged with I1 , the new merged file F+ I1 will be using Normal Compression.
On the next backup, a new delta file is uploaded and delta merge initiated for Job 2 & Job 3.
Job 2 = (F + I1) (Normal Compression)
Job 3 = I2 (No Compression)
Job 4 = I3 (Fast Compression)
Job 5 = I4 (Normal Compression, delta merge initiated)
The new merged file F+ I1 + I2 will not use any compression. In conclusion, the compression type will be updated to the last incremental file in the merge list.
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