<s>
Continuous	B-General_Concept
data	I-General_Concept
protection	I-General_Concept
(	O
CDP	O
)	O
,	O
also	O
called	O
continuous	O
backup	B-Protocol
or	O
real-time	O
backup	B-Protocol
,	O
refers	O
to	O
backup	B-Protocol
of	O
computer	B-General_Concept
data	I-General_Concept
by	O
automatically	O
saving	O
a	O
copy	O
of	O
every	O
change	O
made	O
to	O
that	O
data	O
,	O
essentially	O
capturing	O
every	O
version	O
of	O
the	O
data	O
that	O
the	O
user	O
saves	O
.	O
</s>
<s>
The	O
technique	O
was	O
patented	O
by	O
British	O
entrepreneur	O
Pete	O
Malcolm	O
in	O
1989	O
as	O
"	O
a	O
backup	B-Protocol
system	O
in	O
which	O
a	O
copy	O
[	O
editor	O
's	O
emphasis ]	O
of	O
every	O
change	O
made	O
to	O
a	O
storage	O
medium	O
is	O
recorded	O
as	O
the	O
change	O
occurs	O
[	O
editor	O
's	O
emphasis ]	O
.	O
"	O
</s>
<s>
In	O
an	O
ideal	O
case	O
of	O
continuous	B-General_Concept
data	I-General_Concept
protection	I-General_Concept
,	O
the	O
recovery	O
point	O
objective	O
—	O
"	O
the	O
maximum	O
targeted	O
period	O
in	O
which	O
data	O
(	O
transactions	O
)	O
might	O
be	O
lost	O
from	O
an	O
IT	O
service	O
due	O
to	O
a	O
major	O
incident	O
"	O
—	O
is	O
zero	O
,	O
even	O
though	O
the	O
recovery	O
time	O
objective	O
—	O
"	O
the	O
targeted	O
duration	O
of	O
time	O
and	O
a	O
service	O
level	O
within	O
which	O
a	O
business	O
process	O
must	O
be	O
restored	O
after	O
a	O
disaster	O
(	O
or	O
disruption	O
)	O
in	O
order	O
to	O
avoid	O
unacceptable	O
consequences	O
associated	O
with	O
a	O
break	O
in	O
business	O
continuity	O
"	O
—	O
is	O
not	O
zero	O
.	O
</s>
<s>
True	O
CDP-based	O
solutions	O
can	O
provide	O
fine	O
granularities	B-Operating_System
of	O
restorable	O
objects	O
ranging	O
from	O
crash-consistent	O
images	O
to	O
logical	O
objects	O
such	O
as	O
files	O
,	O
mail	O
boxes	O
,	O
messages	O
,	O
and	O
database	O
files	O
and	O
logs	O
.	O
</s>
<s>
True	O
continuous	B-General_Concept
data	I-General_Concept
protection	I-General_Concept
is	O
different	O
from	O
traditional	O
backup	B-Protocol
in	O
that	O
it	O
is	O
not	O
necessary	O
to	O
specify	O
the	O
point	O
in	O
time	O
to	O
recover	O
from	O
until	O
ready	O
to	O
restore	O
.	O
</s>
<s>
Traditional	O
backups	B-Protocol
only	O
restore	O
data	O
from	O
the	O
time	O
the	O
backup	B-Protocol
was	O
made	O
.	O
</s>
<s>
True	O
continuous	B-General_Concept
data	I-General_Concept
protection	I-General_Concept
,	O
in	O
contrast	O
to	O
"	B-Application
snapshots	I-Application
"	I-Application
,	O
has	O
no	O
backup	B-Protocol
schedules	O
.	O
</s>
<s>
This	O
introduces	O
some	O
overhead	O
to	O
disk-write	O
operations	O
but	O
eliminates	O
the	O
need	O
for	O
scheduled	O
backups	B-Protocol
.	O
</s>
<s>
For	O
example	O
,	O
snapshots	B-Application
[	O
"	O
near-CDP	O
"	O
clarification	O
in	O
the	O
section	O
below ]	O
can	O
provide	O
a	O
reasonable	O
near-CDP-level	O
of	O
protection	O
for	O
file	O
shares	O
,	O
letting	O
users	O
directly	O
access	O
data	O
on	O
the	O
file	O
share	O
at	O
regular	O
intervals	O
—	O
say	O
,	O
every	O
half	O
hour	O
or	O
15	O
minutes	O
.	O
</s>
<s>
That	O
's	O
certainly	O
a	O
higher	O
level	O
of	O
protection	O
than	O
tape-based	O
or	O
disk-based	O
nightly	O
backups	B-Protocol
and	O
may	O
be	O
all	O
you	O
need.	O
"	O
</s>
<s>
Because	O
"	O
near-CDP	O
does	O
this	O
 [ copying ] 	O
at	O
pre-set	O
time	O
intervals	O
"	O
,	O
it	O
is	O
essentially	O
incremental	O
backup	B-Protocol
initiated	O
—	O
separately	O
for	O
each	O
source	O
machine	O
—	O
by	O
timer	O
instead	O
of	O
script	O
.	O
</s>
<s>
Since	O
true	O
CDP	O
"	O
backup	B-Protocol
write	O
operations	O
are	O
executed	O
at	O
the	O
level	O
of	O
the	O
basic	O
input/output	O
system	O
(	O
BIOS	O
)	O
of	O
the	O
microcomputer	O
in	O
such	O
a	O
manner	O
that	O
normal	O
use	O
of	O
the	O
computer	O
is	O
unaffected	O
"	O
,	O
true	O
CDP	O
backup	B-Protocol
must	O
in	O
practice	O
be	O
run	O
in	O
conjunction	O
with	O
a	O
virtual	B-Architecture
machine	I-Architecture
or	O
equivalent	O
—	O
ruling	O
it	O
out	O
for	O
ordinary	O
personal	O
backup	B-Protocol
applications	O
.	O
</s>
<s>
It	O
is	O
therefore	O
discussed	O
in	O
the	O
"	O
Enterprise	B-Protocol
client-server	I-Protocol
backup	I-Protocol
"	O
article	O
,	O
rather	O
than	O
in	O
the	O
"	O
Backup	B-Protocol
"	O
article	O
.	O
</s>
<s>
Some	O
solutions	O
marketed	O
as	O
continuous	B-General_Concept
data	I-General_Concept
protection	I-General_Concept
may	O
only	O
allow	O
restores	O
at	O
fixed	O
intervals	O
such	O
as	O
15	O
minutes	O
or	O
one	O
hour	O
or	O
24	O
hours	O
,	O
because	O
they	O
automatically	O
take	O
incremental	O
backups	B-Protocol
at	O
those	O
intervals	O
.	O
</s>
<s>
Such	O
"	O
near-CDP	O
"	O
—	O
short	O
for	O
near-continuous	O
data	O
protection	O
—	O
schemes	O
are	O
not	O
universally	O
recognized	O
as	O
true	O
continuous	B-General_Concept
data	I-General_Concept
protection	I-General_Concept
,	O
as	O
they	O
do	O
not	O
provide	O
the	O
ability	O
to	O
restore	O
to	O
any	O
point	O
in	O
time	O
.	O
</s>
<s>
When	O
the	O
interval	O
is	O
shorter	O
than	O
one	O
hour	O
,	O
"	O
near-CDP	O
"	O
solutions	O
—	O
for	O
example	O
Arq	O
Backup	B-Protocol
—	O
are	O
typically	O
based	O
on	O
periodic	O
"	B-Application
snapshots	I-Application
"	I-Application
;	O
"	O
to	O
avoid	O
downtime	O
,	O
high-availability	O
systems	O
may	O
instead	O
perform	O
the	O
backup	B-Protocol
on	O
...	O
a	O
read-only	O
copy	O
of	O
the	O
data	O
set	O
frozen	O
at	O
a	O
point	O
in	O
time	O
—	O
and	O
allow	O
applications	O
to	O
continue	O
writing	O
to	O
their	O
data	O
"	O
.	O
</s>
<s>
There	O
is	O
debate	O
in	O
the	O
industry	O
as	O
to	O
whether	O
the	O
granularity	B-Operating_System
of	O
backup	B-Protocol
must	O
be	O
"	O
every	O
write	O
"	O
to	O
be	O
CDP	O
,	O
or	O
whether	O
a	O
"	O
near-CDP	O
"	O
solution	O
that	O
captures	O
the	O
data	O
every	O
few	O
minutes	O
is	O
good	O
enough	O
.	O
</s>
<s>
The	O
latter	O
is	O
sometimes	O
called	O
near	O
continuous	O
backup	B-Protocol
.	O
</s>
<s>
The	O
debate	O
hinges	O
on	O
the	O
use	O
of	O
the	O
term	O
continuous	O
:	O
whether	O
only	O
the	O
backup	B-Protocol
process	O
must	O
be	O
continuously	O
automatically	O
scheduled	O
,	O
which	O
is	O
often	O
sufficient	O
to	O
achieve	O
the	O
benefits	O
cited	O
above	O
,	O
or	O
whether	O
the	O
ability	O
to	O
restore	O
from	O
the	O
backup	B-Protocol
also	O
must	O
be	O
continuous	O
.	O
</s>
<s>
There	O
is	O
a	O
briefer	O
sub-sub-section	O
in	O
the	O
"	O
Backup	B-Protocol
"	O
article	O
about	O
this	O
,	O
now	O
renamed	O
to	O
"	O
Near-CDP	O
"	O
to	O
avoid	O
confusion	O
.	O
</s>
<s>
Continuous	B-General_Concept
data	I-General_Concept
protection	I-General_Concept
differs	O
from	O
RAID	B-Architecture
,	O
replication	B-Architecture
,	O
or	O
mirroring	B-General_Concept
in	O
that	O
these	O
technologies	O
only	O
protect	O
one	O
copy	O
of	O
the	O
data	O
(	O
the	O
most	O
recent	O
)	O
.	O
</s>
<s>
Continuous	B-General_Concept
data	I-General_Concept
protection	I-General_Concept
protects	O
against	O
some	O
effects	O
of	O
data	O
corruption	O
by	O
allowing	O
restoration	O
of	O
a	O
previous	O
,	O
uncorrupted	O
version	O
of	O
the	O
data	O
.	O
</s>
<s>
They	O
could	O
be	O
recovered	O
through	O
other	O
means	O
,	O
such	O
as	O
journaling	B-Application
.	O
</s>
<s>
In	O
some	O
situations	O
,	O
continuous	B-General_Concept
data	I-General_Concept
protection	I-General_Concept
requires	O
less	O
space	O
on	O
backup	B-Protocol
media	O
(	O
usually	O
disk	O
)	O
than	O
traditional	O
backup	B-Protocol
.	O
</s>
<s>
Most	O
continuous	B-General_Concept
data	I-General_Concept
protection	I-General_Concept
solutions	O
save	O
byte	B-Application
or	O
block-level	O
differences	O
rather	O
than	O
file-level	O
differences	O
.	O
</s>
<s>
This	O
means	O
that	O
if	O
one	O
byte	B-Application
of	O
a	O
100	O
GB	O
file	O
is	O
modified	O
,	O
only	O
the	O
changed	O
byte	B-Application
or	O
block	O
is	O
backed	O
up	O
.	O
</s>
<s>
Traditional	O
incremental	O
and	O
differential	O
backups	B-Protocol
make	O
copies	O
of	O
entire	O
files	O
;	O
however	O
starting	O
around	O
2013	O
enterprise	B-Protocol
client-server	I-Protocol
backup	I-Protocol
applications	O
have	O
implemented	O
a	O
capability	O
for	O
block-level	O
incremental	O
backup	B-Protocol
,	O
designed	O
for	O
large	O
files	O
such	O
as	O
databases	O
.	O
</s>
<s>
When	O
real-time	O
edits	O
—	O
especially	O
in	O
multimedia	O
and	O
CAD	B-Application
design	I-Application
environments	O
—	O
are	O
backed	O
up	O
offsite	O
over	O
the	O
upstream	O
channel	O
of	O
the	O
installation	O
's	O
broadband	O
network	O
,	O
network	O
bandwidth	O
throttling	O
may	O
be	O
needed	O
to	O
reduce	O
the	O
impact	O
of	O
true	O
CDP	O
.	O
</s>
<s>
An	O
alternative	O
approach	O
is	O
to	O
back	B-Protocol
up	I-Protocol
to	O
a	O
separate	O
Fibre-Channel-connected	O
SAN	O
appliance	O
.	O
</s>
