<s>
Data	B-Error_Name
scrubbing	I-Error_Name
is	O
an	O
error	B-Error_Name
correction	I-Error_Name
technique	O
that	O
uses	O
a	O
background	O
task	O
to	O
periodically	O
inspect	O
main	O
memory	O
or	O
storage	B-General_Concept
for	O
errors	O
,	O
then	O
corrects	O
detected	O
errors	O
using	O
redundant	B-Application
data	I-Application
in	O
the	O
form	O
of	O
different	O
checksums	B-Algorithm
or	O
copies	O
of	O
data	O
.	O
</s>
<s>
Data	B-Error_Name
scrubbing	I-Error_Name
reduces	O
the	O
likelihood	O
that	O
single	O
correctable	O
errors	O
will	O
accumulate	O
,	O
leading	O
to	O
reduced	O
risks	O
of	O
uncorrectable	O
errors	O
.	O
</s>
<s>
Data	O
integrity	O
is	O
a	O
high-priority	O
concern	O
in	O
writing	O
,	O
reading	O
,	O
storage	B-General_Concept
,	O
transmission	O
,	O
or	O
processing	O
of	O
the	O
computer	B-General_Concept
data	I-General_Concept
in	O
computer	B-General_Concept
operating	I-General_Concept
systems	I-General_Concept
and	O
in	O
computer	B-General_Concept
storage	I-General_Concept
and	O
data	O
transmission	O
systems	O
.	O
</s>
<s>
However	O
,	O
only	O
a	O
few	O
of	O
the	O
currently	O
existing	O
and	O
used	O
file	B-Application
systems	I-Application
provide	O
sufficient	O
protection	O
against	O
data	O
corruption	O
.	O
</s>
<s>
To	O
address	O
this	O
issue	O
,	O
data	B-Error_Name
scrubbing	I-Error_Name
provides	O
routine	O
checks	O
of	O
all	O
inconsistencies	O
in	O
data	O
and	O
,	O
in	O
general	O
,	O
prevention	O
of	O
hardware	O
or	O
software	O
failure	O
.	O
</s>
<s>
This	O
"	O
scrubbing	O
"	O
feature	O
occurs	O
commonly	O
in	O
memory	O
,	O
disk	O
arrays	O
,	O
file	B-Application
systems	I-Application
,	O
or	O
FPGAs	B-Architecture
as	O
a	O
mechanism	O
of	O
error	B-Error_Name
detection	I-Error_Name
and	I-Error_Name
correction	I-Error_Name
.	O
</s>
<s>
With	O
data	B-Error_Name
scrubbing	I-Error_Name
,	O
a	O
RAID	B-Device
controller	I-Device
may	O
periodically	O
read	O
all	O
hard	B-Device
disk	I-Device
drives	I-Device
in	O
a	O
RAID	O
array	O
and	O
check	O
for	O
defective	O
blocks	O
before	O
applications	O
might	O
actually	O
access	O
them	O
.	O
</s>
<s>
In	O
Dell	B-Device
PowerEdge	I-Device
RAID	O
environments	O
,	O
a	O
feature	O
called	O
"	O
patrol	O
read	O
"	O
can	O
perform	O
data	B-Error_Name
scrubbing	I-Error_Name
and	O
preventive	O
maintenance	O
.	O
</s>
<s>
In	O
OpenBSD	B-Operating_System
,	O
the	O
bioctl(8 )	O
utility	O
allows	O
the	O
system	B-Application
administrator	I-Application
to	O
control	O
these	O
patrol	O
reads	O
through	O
the	O
BIOCPATROL	O
ioctl	B-Operating_System
on	O
the	O
/dev/bio	B-Application
pseudo-device	B-Application
;	O
as	O
of	O
2019	O
,	O
this	O
functionality	O
is	O
supported	O
in	O
some	O
device	O
drivers	O
for	O
LSI	O
Logic	O
and	O
Dell	O
controllers	O
—	O
this	O
includes	O
mfi(4 )	O
since	O
OpenBSD	B-Operating_System
5.8	O
(	O
2015	O
)	O
and	O
mfii(4 )	O
since	O
OpenBSD	B-Operating_System
6.4	O
(	O
2018	O
)	O
.	O
</s>
<s>
In	O
FreeBSD	B-Operating_System
and	O
DragonFly	B-Application
BSD	I-Application
,	O
patrol	O
can	O
be	O
controlled	O
through	O
a	O
RAID	O
controller-specific	O
utility	O
mfiutil(8 )	O
since	O
FreeBSD	B-Operating_System
8.0	O
(	O
2009	O
)	O
and	O
7.3	O
(	O
2010	O
)	O
.	O
</s>
<s>
The	O
implementation	O
from	O
FreeBSD	B-Operating_System
was	O
used	O
by	O
the	O
OpenBSD	B-Operating_System
developers	O
for	O
adding	O
patrol	O
support	O
to	O
their	O
generic	O
bio(4 )	O
framework	O
and	O
the	O
bioctl	B-Device
utility	O
,	O
without	O
a	O
need	O
for	O
a	O
separate	O
controller-specific	O
utility	O
.	O
</s>
<s>
In	O
NetBSD	B-Device
in	O
2008	O
,	O
the	O
bio(4 )	O
framework	O
from	O
OpenBSD	B-Operating_System
was	O
extended	O
to	O
feature	O
support	O
for	O
consistency	O
checks	O
,	O
which	O
was	O
implemented	O
for	O
/dev/bio	B-Application
pseudo-device	B-Application
under	O
BIOCSETSTATE	O
ioctl	B-Operating_System
command	O
,	O
with	O
the	O
options	O
being	O
start	O
and	O
stop	O
(	O
BIOC_SSCHECKSTART_VOL	O
and	O
BIOC_SSCHECKSTOP_VOL	O
,	O
respectively	O
)	O
;	O
this	O
is	O
supported	O
only	O
by	O
a	O
single	O
driver	O
as	O
of	O
2019	O
—	O
arcmsr(4 )	O
.	O
</s>
<s>
Linux	B-Application
MD	I-Application
RAID	I-Application
,	O
as	O
a	O
software	O
RAID	O
implementation	O
,	O
makes	O
data	O
consistency	O
checks	O
available	O
and	O
provides	O
automated	O
repairing	O
of	O
detected	O
data	O
inconsistencies	O
.	O
</s>
<s>
Such	O
procedures	O
are	O
usually	O
performed	O
by	O
setting	O
up	O
a	O
weekly	O
cron	B-General_Concept
job	I-General_Concept
.	O
</s>
<s>
As	O
a	O
copy-on-write	B-Language
(	O
CoW	O
)	O
file	B-Application
system	I-Application
for	O
Linux	B-Application
,	O
Btrfs	B-Operating_System
provides	O
fault	O
isolation	O
,	O
corruption	O
detection	O
and	O
correction	O
,	O
and	O
file-system	B-Application
scrubbing	O
.	O
</s>
<s>
If	O
the	O
file	B-Application
system	I-Application
detects	O
a	O
checksum	B-Algorithm
mismatch	O
while	O
reading	O
a	O
block	O
,	O
it	O
first	O
tries	O
to	O
obtain	O
(	O
or	O
create	O
)	O
a	O
good	O
copy	O
of	O
this	O
block	O
from	O
another	O
device	O
if	O
its	O
internal	O
mirroring	O
or	O
RAID	O
techniques	O
are	O
in	O
use	O
.	O
</s>
<s>
Btrfs	B-Operating_System
can	O
initiate	O
an	O
online	O
check	O
of	O
the	O
entire	O
file	B-Application
system	I-Application
by	O
triggering	O
a	O
file	B-Application
system	I-Application
scrub	O
job	O
that	O
is	O
performed	O
in	O
the	O
background	O
.	O
</s>
<s>
The	O
scrub	O
job	O
scans	O
the	O
entire	O
file	B-Application
system	I-Application
for	O
integrity	O
and	O
automatically	O
attempts	O
to	O
report	O
and	O
repair	O
any	O
bad	O
blocks	O
it	O
finds	O
along	O
the	O
way	O
.	O
</s>
<s>
The	O
features	O
of	O
ZFS	O
,	O
which	O
is	O
a	O
combined	O
file	B-Application
system	I-Application
and	O
logical	B-Application
volume	I-Application
manager	I-Application
,	O
include	O
the	O
verification	O
against	O
data	O
corruption	O
modes	O
,	O
continuous	O
integrity	O
checking	O
,	O
and	O
automatic	O
repair	O
.	O
</s>
<s>
This	O
can	O
be	O
a	O
problem	O
for	O
DRAM	O
-	O
and	O
SRAM-based	O
memories	O
.	O
</s>
<s>
Memory	O
scrubbing	O
does	O
error-detection	O
and	O
correction	O
of	O
bit	O
errors	O
in	O
computer	O
RAM	B-Architecture
by	O
using	O
ECC	B-General_Concept
memory	I-General_Concept
,	O
other	O
copies	O
of	O
the	O
data	O
,	O
or	O
other	O
error-correction	B-Error_Name
codes	O
.	O
</s>
<s>
Scrubbing	O
is	O
a	O
technique	O
used	O
to	O
reprogram	O
an	O
FPGA	B-Architecture
.	O
</s>
<s>
Numerous	O
approaches	O
can	O
be	O
taken	O
with	O
respect	O
to	O
scrubbing	O
,	O
from	O
simply	O
reprogramming	O
the	O
FPGA	B-Architecture
to	O
partial	O
reconfiguration	O
.	O
</s>
<s>
The	O
simplest	O
method	O
of	O
scrubbing	O
is	O
to	O
completely	O
reprogram	O
the	O
FPGA	B-Architecture
at	O
some	O
periodic	O
rate	O
(	O
typically	O
1/10	O
the	O
calculated	O
upset	O
rate	O
)	O
.	O
</s>
<s>
However	O
,	O
the	O
FPGA	B-Architecture
is	O
not	O
operational	O
during	O
that	O
reprogram	O
time	O
,	O
on	O
the	O
order	O
of	O
micro	O
to	O
milliseconds	O
.	O
</s>
<s>
This	O
technique	O
allows	O
the	O
FPGA	B-Architecture
to	O
be	O
reprogrammed	O
while	O
still	O
operational	O
.	O
</s>
