<s>
A	O
differential	B-General_Concept
backup	I-General_Concept
is	O
a	O
type	O
of	O
data	B-Protocol
backup	I-Protocol
that	O
preserves	O
data	O
,	O
saving	O
only	O
the	O
difference	O
in	O
the	O
data	O
since	O
the	O
last	O
full	B-Protocol
backup	I-Protocol
.	O
</s>
<s>
The	O
rationale	O
in	O
this	O
is	O
that	O
,	O
since	O
changes	O
to	O
data	O
are	O
generally	O
few	O
compared	O
to	O
the	O
entire	O
amount	O
of	O
data	O
in	O
the	O
data	O
repository	O
,	O
the	O
amount	O
of	O
time	O
required	O
to	O
complete	O
the	O
backup	B-Protocol
will	O
be	O
smaller	O
than	O
if	O
a	O
full	B-Protocol
backup	I-Protocol
was	O
performed	O
every	O
time	O
that	O
the	O
organization	O
or	O
data	O
owner	O
wishes	O
to	O
back	B-Protocol
up	I-Protocol
changes	O
since	O
the	O
last	O
full	B-Protocol
backup	I-Protocol
.	O
</s>
<s>
Another	O
advantage	O
,	O
at	O
least	O
as	O
compared	O
to	O
the	O
incremental	B-General_Concept
backup	I-General_Concept
method	O
of	O
data	B-Protocol
backup	I-Protocol
,	O
is	O
that	O
at	O
data	O
restoration	O
time	O
,	O
at	O
most	O
two	O
backup	B-Protocol
media	O
are	O
ever	O
needed	O
to	O
restore	O
all	O
the	O
data	O
.	O
</s>
<s>
A	O
differential	B-General_Concept
backup	I-General_Concept
is	O
a	O
cumulative	O
backup	B-Protocol
of	O
all	O
changes	O
made	O
since	O
the	O
last	O
full	B-Protocol
backup	I-Protocol
,	O
i.e.	O
,	O
the	O
differences	O
since	O
the	O
last	O
full	B-Protocol
backup	I-Protocol
.	O
</s>
<s>
The	O
advantage	O
to	O
this	O
is	O
the	O
quicker	O
recovery	O
time	O
,	O
requiring	O
only	O
a	O
full	B-Protocol
backup	I-Protocol
and	O
the	O
last	O
differential	B-General_Concept
backup	I-General_Concept
to	O
restore	O
the	O
entire	O
data	O
repository	O
.	O
</s>
<s>
The	O
disadvantage	O
is	O
that	O
for	O
each	O
day	O
elapsed	O
since	O
the	O
last	O
full	B-Protocol
backup	I-Protocol
,	O
more	O
data	O
needs	O
to	O
be	O
backed	O
up	O
,	O
especially	O
if	O
a	O
significant	O
proportion	O
of	O
the	O
data	O
has	O
changed	O
,	O
thus	O
increasing	O
backup	B-Protocol
time	O
as	O
compared	O
to	O
the	O
incremental	B-General_Concept
backup	I-General_Concept
method	O
.	O
</s>
<s>
It	O
is	O
important	O
to	O
use	O
the	O
terms	O
"	O
differential	B-General_Concept
backup	I-General_Concept
"	O
and	O
"	O
incremental	B-General_Concept
backup	I-General_Concept
"	O
correctly	O
.	O
</s>
<s>
A	O
differential	B-General_Concept
backup	I-General_Concept
refers	O
to	O
a	O
backup	B-Protocol
made	O
to	O
include	O
the	O
differences	O
since	O
the	O
last	O
full	B-Protocol
backup	I-Protocol
,	O
while	O
an	O
incremental	B-General_Concept
backup	I-General_Concept
contains	O
only	O
the	O
changes	O
since	O
the	O
last	O
incremental	B-General_Concept
backup	I-General_Concept
.	O
</s>
<s>
(	O
Or	O
,	O
of	O
course	O
,	O
since	O
the	O
last	O
full	B-Protocol
backup	I-Protocol
if	O
the	O
incremental	B-General_Concept
backup	I-General_Concept
in	O
questions	O
is	O
the	O
first	O
incremental	B-General_Concept
backup	I-General_Concept
immediately	O
after	O
the	O
last	O
full	B-Protocol
backup	I-Protocol
.	O
)	O
</s>
<s>
All	O
the	O
major	O
data	B-Protocol
backup	I-Protocol
vendors	O
have	O
standardized	O
on	O
these	O
definitions	O
.	O
</s>
<s>
The	O
difference	O
between	O
incremental	O
and	O
differential	B-General_Concept
backups	I-General_Concept
can	O
be	O
illustrated	O
as	O
follows	O
:	O
</s>
<s>
Incremental	B-General_Concept
backups	I-General_Concept
:	O
</s>
<s>
The	O
above	O
assumes	O
that	O
backups	B-Protocol
are	O
done	O
daily	O
.	O
</s>
<s>
Otherwise	O
,	O
the	O
“	O
Changes	O
since	O
”	O
entry	O
must	O
be	O
modified	O
to	O
refer	O
to	O
the	O
last	O
backup	B-Protocol
(	O
whether	O
such	O
last	O
backup	B-Protocol
was	O
full	O
or	O
incremental	O
)	O
.	O
</s>
<s>
It	O
also	O
assumes	O
a	O
weekly	O
rotation	B-Device
.	O
</s>
<s>
Differential	B-General_Concept
backups	I-General_Concept
:	O
</s>
<s>
For	O
example	O
,	O
Oracle	B-Application
Corporation	I-Application
uses	O
a	O
backward	O
description	O
of	O
differential	B-General_Concept
backups	I-General_Concept
in	O
their	O
DB	O
product	O
as	O
of	O
May	O
14	O
,	O
2015	O
:	O
</s>
<s>
"	O
Differential	O
incremental	B-General_Concept
backups	I-General_Concept
-	O
In	O
a	O
differential	O
level	O
1	O
backup	B-Protocol
,	O
RMAN	O
backs	O
up	O
all	O
blocks	O
that	O
have	O
changed	O
since	O
the	O
most	O
recent	O
cumulative	O
or	O
differential	O
incremental	B-General_Concept
backup	I-General_Concept
,	O
whether	O
at	O
level	O
1	O
or	O
level	O
0	O
.	O
</s>
<s>
RMAN	O
determines	O
which	O
level	O
1	O
backup	B-Protocol
occurred	O
most	O
recently	O
and	O
backs	O
up	O
all	O
blocks	O
modified	O
after	O
that	O
backup	B-Protocol
.	O
</s>
<s>
If	O
no	O
level	O
1	O
is	O
available	O
,	O
RMAN	O
copies	O
all	O
blocks	O
changed	O
since	O
the	O
level	O
0	O
backup.	O
"	O
</s>
