<s>
In	O
computer	O
main	O
memory	O
,	O
auxiliary	O
storage	B-General_Concept
and	O
computer	B-General_Concept
buses	I-General_Concept
,	O
data	B-Application
redundancy	I-Application
is	O
the	O
existence	O
of	O
data	O
that	O
is	O
additional	O
to	O
the	O
actual	O
data	O
and	O
permits	O
correction	O
of	O
errors	O
in	O
stored	O
or	O
transmitted	O
data	O
.	O
</s>
<s>
The	O
additional	O
data	O
can	O
simply	O
be	O
a	O
complete	O
copy	O
of	O
the	O
actual	O
data	O
(	O
a	O
type	O
of	O
repetition	B-Error_Name
code	I-Error_Name
)	O
,	O
or	O
only	O
select	O
pieces	O
of	O
data	O
that	O
allow	O
detection	B-Error_Name
of	I-Error_Name
errors	I-Error_Name
and	I-Error_Name
reconstruction	I-Error_Name
of	O
lost	O
or	O
damaged	O
data	O
up	O
to	O
a	O
certain	O
level	O
.	O
</s>
<s>
For	O
example	O
,	O
by	O
including	O
computed	O
check	O
bits	O
,	O
ECC	B-General_Concept
memory	I-General_Concept
is	O
capable	O
of	O
detecting	O
and	O
correcting	O
single-bit	O
errors	O
within	O
each	O
memory	O
word	O
,	O
while	O
RAID	O
1	O
combines	O
two	O
hard	B-Device
disk	I-Device
drives	I-Device
(	O
HDDs	O
)	O
into	O
a	O
logical	O
storage	B-General_Concept
unit	O
that	O
allows	O
stored	O
data	O
to	O
survive	O
a	O
complete	O
failure	O
of	O
one	O
drive	O
.	O
</s>
<s>
Data	B-Application
redundancy	I-Application
can	O
also	O
be	O
used	O
as	O
a	O
measure	O
against	O
silent	O
data	O
corruption	O
;	O
for	O
example	O
,	O
file	B-Application
systems	I-Application
such	O
as	O
Btrfs	B-Operating_System
and	O
ZFS	B-Application
use	O
data	O
and	O
metadata	O
checksumming	O
in	O
combination	O
with	O
copies	O
of	O
stored	O
data	O
to	O
detect	O
silent	O
data	O
corruption	O
and	O
repair	O
its	O
effects	O
.	O
</s>
<s>
While	O
different	O
in	O
nature	O
,	O
data	B-Application
redundancy	I-Application
also	O
occurs	O
in	O
database	B-Application
systems	I-Application
that	O
have	O
values	O
repeated	O
unnecessarily	O
in	O
one	O
or	O
more	O
records	O
or	O
fields	B-Application
,	O
within	O
a	O
table	B-Application
,	O
or	O
where	O
the	O
field	O
is	O
replicated/repeated	O
in	O
two	O
or	O
more	O
tables	O
.	O
</s>
<s>
Often	O
this	O
is	O
found	O
in	O
unnormalized	B-Application
database	O
designs	O
and	O
results	O
in	O
the	O
complication	O
of	O
database	O
management	O
,	O
introducing	O
the	O
risk	O
of	O
corrupting	O
the	O
data	O
,	O
and	O
increasing	O
the	O
required	O
amount	O
of	O
storage	B-General_Concept
.	O
</s>
<s>
For	O
instance	O
,	O
when	O
customer	O
data	O
are	O
duplicated	O
and	O
attached	O
with	O
each	O
product	O
bought	O
,	O
then	O
redundancy	B-General_Concept
of	O
data	O
is	O
a	O
known	O
source	O
of	O
inconsistency	B-General_Concept
since	O
a	O
given	O
customer	O
might	O
appear	O
with	O
different	O
values	O
for	O
one	O
or	O
more	O
of	O
their	O
attributes	O
.	O
</s>
<s>
Data	B-Application
redundancy	I-Application
leads	O
to	O
data	B-Application
anomalies	I-Application
and	O
corruption	O
and	O
generally	O
should	O
be	O
avoided	O
by	O
design	O
;	O
applying	O
database	B-Application
normalization	I-Application
prevents	O
redundancy	B-General_Concept
and	O
makes	O
the	O
best	O
possible	O
usage	O
of	O
storage	B-General_Concept
.	O
</s>
