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With
In-File Delta technology, it is now possible to backup
very large files daily. There are two different modes of
operation available (“Differential” and “Incremental”)
for In-File Delta backups. Both modes will use
approximately the same amount of disk space storage on
the server.
“Differential Delta” will facilitate ease of restore.
The delta is generated by comparing with the latest
uploaded “Full” file so the delta file can grow daily
and uses more bandwidth during backup. For restoration,
the full file and a single delta file is required to
restore the file to a specific point-in-time.
“Incremental Delta” will facilitate ease of backup. The
delta is generated by comparing with the latest uploaded
“Full” or “Delta” file so the delta file is the smallest
possible and uses the least bandwidth during backup. For
restoration, the full file and all delta files up to the
required point-in-time is required to restore the file
to a specific point-in-time.
The
major differences are summarized in the following table:
|
In-File Delta Technology |
Pros |
Cons |
|
Differential
Always use the latest uploaded “Full” file
to generate the delta file. |
For restore, just need the full and a delta
to recover to a specific point-in-time. |
The daily delta file will be larger than
incremental delta and needs more bandwidth
to upload. |
|
Incremental
Always use the latest uploaded file (whether
“Full” or “Delta”) to generate the delta
file. |
Daily delta file only shows the difference
between the current file and previous upload
file. The incremental delta file will be
smaller than the differential delta file and
so should upload faster. |
For restore, need to use the full and all
deltas up to the point-in-time to recover to
a specific point-in-time. If any delta file
is corrupted, the file can only be recovered
up to the point-in-time before the corrupted
delta. |
The
delta is generated by extracting the differences between
the latest file to backup and the original file stored
on the server. Both files are divided into individual
blocks using the same block size and the blocks compared
to determine whether they’re the same or different. The
differences are extracted into the delta file.
Using a different block size setting can affect the
speed of generation and size of the generated delta.
Generally speaking, the relationship between the block
size setting and the delta generated is as follows:
-
The smaller the block size, the delta file generated
will be smaller but takes longer to process.
-
The larger the block size, the delta file generated
will be larger but is faster to process.
The
block size setting available are Auto, 1K, 2K, 4K, 8K,
16K, 32K, 64K, 128K, 256K, 512K and 1M. With “Auto”, the
block size used will be initially set using the backup
file size according to the table below:
|
Initial Full File Size |
Auto Block Size Used |
|
>
15G |
64K |
|
>
8G
£
15G |
32K |
|
>
2G
£
8G |
16K |
|
>
500M
£
2G |
8K |
|
£
500M |
4K |
Assume the initial full file is 100MB and grows
daily by 10MB.
The files uploaded to the server and the approximate
storage space required is as follows:
|
# |
File
Size |
Daily Upload to Server |
Storage Space Required (MB) |
|
Differential |
Incremental |
Differential |
Incremental |
|
1 |
100MB |
 Full
File = 100MB |
 Full
File = 100MB |
(Full) 100
Total = 100 |
(Full) 100
Total = 100 |
|
2 |
110MB |
 Delta
= 10MB |
 Delta1
= 10MB |
(Full) 100
+ (Delta) 10
Total = 110 |
(Full) 100
+ (Delta1) 10
Total = 110 |
|
3 |
120MB |
 Delta
= 20MB |
 Delta2
= 10MB |
(Full) 100
+ (Delta) 20
Total = 120 |
(Full) 100
+ (Delta1) 10
+ (Delta2) 10
Total = 120 |
|
4 |
130MB |
 Delta
= 30MB |
 Delta3
= 10MB |
(Full) 100
+ (Delta) 30
Total = 130 |
(Full) 100
+ (Delta1) 10
+ (Delta2) 10
+ (Delta3) 10
Total = 130 |
* Storage space is approximate
Assume restoring the various files backed up above.
|
# |
Files Downloaded from OBS to Restore |
|
Differential |
Incremental |
|
1 |
 |
|
|
2 |
 |
 |
|
3 |
 |
 |
|
4 |
 |
 |
|
