<s>
In	O
digital	B-General_Concept
storage	I-General_Concept
,	O
a	O
Medium	B-Device
Error	I-Device
is	O
a	O
class	O
of	O
errors	B-Error_Name
that	O
a	O
storage	O
device	O
can	O
experience	O
,	O
which	O
imply	O
that	O
a	O
physical	O
problem	O
was	O
encountered	O
when	O
trying	O
to	O
access	O
the	O
device	O
.	O
</s>
<s>
The	O
word	O
"	O
medium	O
"	O
refers	O
to	O
the	O
physical	O
storage	O
layer	O
,	O
the	O
medium	O
on	O
which	O
the	O
data	O
is	O
stored	O
;	O
as	O
opposed	O
to	O
errors	B-Error_Name
related	O
to	O
e.g.	O
</s>
<s>
Medium	B-Device
errors	I-Device
are	O
most	O
commonly	O
detected	O
by	O
checking	O
the	O
read	O
data	O
against	O
a	O
checksum	B-Algorithm
–	O
itself	O
being	O
most	O
commonly	O
also	O
stored	O
on	O
the	O
same	O
device	O
.	O
</s>
<s>
The	O
mismatch	O
of	O
data	O
to	O
its	O
supposed	O
checksum	B-Algorithm
is	O
assumed	O
to	O
be	O
caused	O
by	O
the	O
data	O
being	O
corrupted	O
.	O
</s>
<s>
Locations	O
of	O
medium	B-Device
errors	I-Device
can	O
be	O
either	O
temporary	O
(	O
as	O
in	O
the	O
case	O
of	O
bit	O
rot	O
–	O
there	O
is	O
no	O
damage	O
to	O
the	O
medium	O
,	O
the	O
data	O
was	O
simply	O
lost	O
)	O
,	O
or	O
permanent	O
(	O
as	O
in	O
the	O
case	O
of	O
scratching	O
–	O
the	O
physical	O
location	O
is	O
unusable	O
from	O
that	O
point	O
onwards	O
)	O
.	O
</s>
<s>
Devices	O
can	O
sometimes	O
recover	O
from	O
medium	B-Device
errors	I-Device
,	O
either	O
by	O
retrying	O
or	O
by	O
managing	O
to	O
reconcile	O
the	O
data	O
with	O
the	O
checksum	B-Algorithm
.	O
</s>
<s>
Medium	B-Device
errors	I-Device
are	O
often	O
associated	O
with	O
long	O
latency	O
for	O
the	O
IOs	O
.	O
</s>
