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Table 3 1 TB File Server Backup
1st daily full backup
1st daily incremental backup
2nd daily incremental backup
3rd daily incremental backup
4th daily incremental backup
5th daily incremental backup
2nd weekly full backup
3rd weekly full backup
...
25th weekly full backup
Total
Approximately 1 1:1 reduction in data stored
Table 4 (page 16)
using deduplication. As shown, deduplication ratios depend on the backup policy and on the
percentage of change between backups.
Table 4 Deduplication Ratio Impact
Daily change
rate
0.5%
1.0%
2.0%
*4 months = 5 daily + 17 weekly backups
See
"Performance" (page 94)
performance.
Target-based Deduplication
VLS and D2D deduplication is target-based; the process is running transparently inside the hardware.
This means that when the data is read (by copying to physical tape, restoring a backup, etc.), the
device rebuilds the data. The data that is read is identical to the data that was originally written
(like tape drive compression); there are no pointers in the read data.
Tape Oversubscription
Deduplication requires more virtual tape capacity than physical disk; this is sometimes called tape
oversubscription. The purpose of deduplication is to reduce the amount of disk required to store
multiple generations of backups. Be sure to create enough virtual tape capacity to contain your
entire retention policy, and the amount of physical disk will be much less capacity due to
deduplication.
For example, if you are backing up 50 TB per week and retaining four weeks, you need to create
enough virtual tape capacity (after compression) to store 200 TB of backups. If you have 2:1
16
Concepts
Data stored normally
500 GB
50 GB
50 GB
50 GB
50 GB
50 GB
500 GB
500 GB
500 GB
12,750 GB
is an example that may not reflect the savings that all environments achieve
Daily full and weekly full
4 months*
6 months
15:1
19:1
12:1
13:1
8:1
9:1
for additional information on optimizing your deduplication
Data stored with deduplication
500 GB
5 GB
5 GB
5 GB
5 GB
5 GB
25 GB
25 GB
25 GB
1,125 GB
Backup policy
Daily incremental (10%) and weekly full
1 year
4 months*
25:1
12:1
16:1
10:1
9:1
7:1
6 months
1 year
16:1
23:1
1 1:1
15:1
7:1
9:1
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