<s>
A	O
hard	B-Device
disk	I-Device
drive	I-Device
failure	I-Device
occurs	O
when	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
malfunctions	O
and	O
the	O
stored	O
information	O
cannot	O
be	O
accessed	O
with	O
a	O
properly	O
configured	O
computer	O
.	O
</s>
<s>
A	O
hard	B-Device
disk	I-Device
failure	I-Device
may	O
occur	O
in	O
the	O
course	O
of	O
normal	O
operation	O
,	O
or	O
due	O
to	O
an	O
external	O
factor	O
such	O
as	O
exposure	O
to	O
fire	O
or	O
water	O
or	O
high	O
magnetic	O
fields	O
,	O
or	O
suffering	O
a	O
sharp	O
impact	O
or	O
environmental	O
contamination	O
,	O
which	O
can	O
lead	O
to	O
a	O
head	O
crash	O
.	O
</s>
<s>
The	O
stored	O
information	O
on	O
a	O
hard	B-Device
drive	I-Device
may	O
also	O
be	O
rendered	O
inaccessible	O
as	O
a	O
result	O
of	O
data	O
corruption	O
,	O
disruption	O
or	O
destruction	O
of	O
the	O
hard	B-Device
drive	I-Device
's	O
master	B-Device
boot	I-Device
record	I-Device
,	O
or	O
by	O
malware	O
deliberately	O
destroying	O
the	O
disk	O
's	O
contents	O
.	O
</s>
<s>
There	O
are	O
a	O
number	O
of	O
causes	O
for	O
hard	B-Device
drives	I-Device
to	O
fail	O
including	O
:	O
human	O
error	O
,	O
hardware	O
failure	O
,	O
firmware	O
corruption	O
,	O
media	O
damage	O
,	O
heat	O
,	O
water	O
damage	O
,	O
power	O
issues	O
and	O
mishaps	O
.	O
</s>
<s>
Hard	B-Device
disk	I-Device
drive	I-Device
failures	I-Device
tend	O
to	O
follow	O
the	O
concept	O
of	O
the	O
bathtub	O
curve	O
.	O
</s>
<s>
The	O
most	O
notorious	O
cause	O
of	O
drive	O
failure	O
is	O
a	O
head	O
crash	O
,	O
where	O
the	O
internal	O
read-and-write	B-Device
head	I-Device
of	O
the	O
device	O
,	O
usually	O
just	O
hovering	O
above	O
the	O
surface	O
,	O
touches	O
a	O
platter	B-Device
,	O
or	O
scratches	O
the	O
magnetic	O
data-storage	B-General_Concept
surface	O
.	O
</s>
<s>
A	O
head	O
crash	O
usually	O
incurs	O
severe	O
data	B-General_Concept
loss	I-General_Concept
,	O
and	O
data	B-Application
recovery	I-Application
attempts	O
may	O
cause	O
further	O
damage	O
if	O
not	O
done	O
by	O
a	O
specialist	O
with	O
proper	O
equipment	O
.	O
</s>
<s>
Drive	B-Device
platters	I-Device
are	O
coated	O
with	O
an	O
extremely	O
thin	O
layer	O
of	O
non-electrostatic	O
lubricant	O
,	O
so	O
that	O
the	O
read-and-write	B-Device
head	I-Device
will	O
likely	O
simply	O
glance	O
off	O
the	O
surface	O
of	O
the	O
platter	B-Device
should	O
a	O
collision	O
occur	O
.	O
</s>
<s>
However	O
,	O
this	O
head	O
hovers	O
mere	O
nanometers	O
from	O
the	O
platter	B-Device
's	O
surface	O
which	O
makes	O
a	O
collision	O
an	O
acknowledged	O
risk	O
.	O
</s>
<s>
If	O
the	O
filter	O
fails	O
to	O
capture	O
a	O
dust	O
particle	O
,	O
the	O
particle	O
can	O
land	O
on	O
the	O
platter	B-Device
,	O
causing	O
a	O
head	O
crash	O
if	O
the	O
head	O
happens	O
to	O
sweep	O
over	O
it	O
.	O
</s>
<s>
After	O
a	O
head	O
crash	O
,	O
particles	O
from	O
the	O
damaged	O
platter	B-Device
and	O
head	O
media	O
can	O
cause	O
one	O
or	O
more	O
bad	B-Device
sectors	I-Device
.	O
</s>
<s>
These	O
,	O
in	O
addition	O
to	O
platter	B-Device
damage	O
,	O
will	O
quickly	O
render	O
a	O
drive	O
useless	O
.	O
</s>
<s>
In	O
the	O
late	O
1990s	O
,	O
Iomega	O
's	O
100-megabyte	O
Zip	B-Operating_System
disks	I-Operating_System
used	O
in	O
Zip	B-Operating_System
drives	I-Operating_System
were	O
affected	O
by	O
the	O
click	B-Error_Name
of	I-Error_Name
death	I-Error_Name
,	O
called	O
so	O
because	O
the	O
drives	O
endlessly	O
clicked	O
when	O
accessed	O
,	O
indicating	O
the	O
impending	O
failure	O
.	O
</s>
<s>
3.5-inch	O
floppy	B-Device
disks	I-Device
can	O
also	O
fall	O
victim	O
to	O
disk	O
failure	O
.	O
</s>
<s>
Failure	O
of	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
can	O
be	O
catastrophic	O
or	O
gradual	O
.	O
</s>
<s>
The	O
former	O
typically	O
presents	O
as	O
a	O
drive	O
that	O
can	O
no	O
longer	O
be	O
detected	O
by	O
CMOS	B-Device
setup	I-Device
,	O
or	O
that	O
fails	O
to	O
pass	O
BIOS	B-Device
POST	I-Device
so	O
that	O
the	O
operating	O
system	O
never	O
sees	O
it	O
.	O
</s>
<s>
Gradual	O
hard-drive	B-Device
failure	O
can	O
be	O
harder	O
to	O
diagnose	O
,	O
because	O
its	O
symptoms	O
,	O
such	O
as	O
corrupted	O
data	O
and	O
slowing	O
down	O
of	O
the	O
PC	O
(	O
caused	O
by	O
gradually	O
failing	O
areas	O
of	O
the	O
hard	B-Device
drive	I-Device
requiring	O
repeated	O
read	O
attempts	O
before	O
successful	O
access	O
)	O
,	O
can	O
be	O
caused	O
by	O
many	O
other	O
computer	O
issues	O
,	O
such	O
as	O
malware	O
.	O
</s>
<s>
A	O
rising	O
number	O
of	O
bad	B-Device
sectors	I-Device
can	O
be	O
a	O
sign	O
of	O
a	O
failing	B-Device
hard	I-Device
drive	I-Device
,	O
but	O
because	O
the	O
hard	B-Device
drive	I-Device
automatically	O
adds	O
them	O
to	O
its	O
own	O
growth	O
defect	O
table	O
,	O
they	O
may	O
not	O
become	O
evident	O
to	O
utilities	O
such	O
as	O
ScanDisk	O
unless	O
the	O
utility	O
can	O
catch	O
them	O
before	O
the	O
hard	B-Device
drive	I-Device
's	O
defect	O
management	O
system	O
does	O
,	O
or	O
the	O
backup	B-Protocol
sectors	O
held	O
in	O
reserve	O
by	O
the	O
internal	B-Device
hard-drive	I-Device
defect	I-Device
management	I-Device
system	O
run	O
out	O
(	O
by	O
which	O
point	O
the	O
drive	O
is	O
on	O
the	O
point	O
of	O
failing	O
outright	O
)	O
.	O
</s>
<s>
A	O
cyclical	O
repetitive	O
pattern	O
of	O
seek	O
activity	O
such	O
as	O
rapid	O
or	O
slower	O
seek-to-end	O
noises	O
(	O
click	B-Error_Name
of	I-Error_Name
death	I-Error_Name
)	O
can	O
be	O
indicative	O
of	O
hard	B-Device
drive	I-Device
problems	O
.	O
</s>
<s>
Modern	O
HDDs	O
prevent	O
power	O
interruptions	O
or	O
other	O
malfunctions	O
from	O
landing	O
its	O
heads	O
in	O
the	O
data	O
zone	O
by	O
either	O
physically	O
moving	O
(	O
parking	O
)	O
the	O
heads	O
to	O
a	O
special	O
landing	O
zone	O
on	O
the	O
platters	O
that	O
is	O
not	O
used	O
for	O
data	B-General_Concept
storage	I-General_Concept
,	O
or	O
by	O
physically	O
locking	O
the	O
heads	O
in	O
a	O
suspended	O
(	O
unloaded	O
)	O
position	O
raised	O
off	O
the	O
platters	O
.	O
</s>
<s>
A	O
landing	O
zone	O
is	O
an	O
area	O
of	O
the	O
platter	B-Device
usually	O
near	O
its	O
inner	O
diameter	O
(	O
ID	O
)	O
,	O
where	O
no	O
data	O
is	O
stored	O
.	O
</s>
<s>
Spring	O
tension	O
from	O
the	O
head	O
mounting	O
constantly	O
pushes	O
the	O
heads	O
towards	O
the	O
platter	B-Device
.	O
</s>
<s>
For	O
example	O
,	O
the	O
Seagate	O
Barracuda	O
7200.10	O
series	O
of	O
desktop	O
hard	B-Device
disk	I-Device
drives	I-Device
are	O
rated	O
to	O
50,000	O
startstop	O
cycles	O
;	O
in	O
other	O
words	O
,	O
no	O
failures	O
attributed	O
to	O
the	O
headplatter	O
interface	O
were	O
seen	O
before	O
at	O
least	O
50,000	O
startstop	O
cycles	O
during	O
testing	O
.	O
</s>
<s>
In	O
general	O
,	O
CSS	O
technology	O
can	O
be	O
prone	O
to	O
increased	O
stiction	O
(	O
the	O
tendency	O
for	O
the	O
heads	O
to	O
stick	O
to	O
the	O
platter	B-Device
surface	O
)	O
,	O
e.g.	O
</s>
<s>
Excessive	O
stiction	O
can	O
cause	O
physical	O
damage	O
to	O
the	O
platter	B-Device
and	O
slider	O
or	O
spindle	O
motor	O
.	O
</s>
<s>
The	O
first	O
HDD	O
RAMAC	B-Device
and	O
most	O
early	O
disk	B-General_Concept
drives	I-General_Concept
used	O
complex	O
mechanisms	O
to	O
load	O
and	O
unload	O
the	O
heads	O
.	O
</s>
<s>
Addressing	O
shock	O
robustness	O
,	O
IBM	O
also	O
created	O
a	O
technology	O
for	O
their	O
ThinkPad	B-Operating_System
line	O
of	O
laptop	O
computers	O
called	O
the	O
Active	O
Protection	O
System	O
.	O
</s>
<s>
When	O
a	O
sudden	O
,	O
sharp	O
movement	O
is	O
detected	O
by	O
the	O
built-in	O
accelerometer	O
in	O
the	O
ThinkPad	B-Operating_System
,	O
internal	O
hard	B-Device
disk	I-Device
heads	I-Device
automatically	O
unload	O
themselves	O
to	O
reduce	O
the	O
risk	O
of	O
any	O
potential	O
data	B-General_Concept
loss	I-General_Concept
or	O
scratch	O
defects	O
.	O
</s>
<s>
Apple	O
later	O
also	O
utilized	O
this	O
technology	O
in	O
their	O
PowerBook	B-Device
,	O
iBook	B-Device
,	O
MacBook	B-Device
Pro	I-Device
,	O
and	O
MacBook	B-Device
line	O
,	O
known	O
as	O
the	O
Sudden	B-Device
Motion	I-Device
Sensor	I-Device
.	O
</s>
<s>
Hard	B-Device
drives	I-Device
may	O
fail	O
in	O
a	O
number	O
of	O
ways	O
.	O
</s>
<s>
Earlier	O
drives	O
had	O
a	O
tendency	O
toward	O
developing	O
bad	B-Device
sectors	I-Device
with	O
use	O
and	O
wear	O
;	O
these	O
bad	B-Device
sectors	I-Device
could	O
be	O
"	O
mapped	O
out	O
"	O
so	O
they	O
were	O
not	O
used	O
and	O
did	O
not	O
affect	O
operation	O
of	O
a	O
drive	O
,	O
and	O
this	O
was	O
considered	O
normal	O
unless	O
many	O
bad	B-Device
sectors	I-Device
developed	O
in	O
a	O
short	O
period	O
of	O
time	O
.	O
</s>
<s>
Some	O
early	O
drives	O
even	O
had	O
a	O
table	O
attached	O
to	O
a	O
drive	O
's	O
case	O
on	O
which	O
bad	B-Device
sectors	I-Device
were	O
to	O
be	O
listed	O
as	O
they	O
appeared	O
.	O
</s>
<s>
Later	O
drives	O
map	O
out	O
bad	B-Device
sectors	I-Device
automatically	O
,	O
in	O
a	O
way	O
invisible	O
to	O
the	O
user	O
;	O
a	O
drive	O
with	O
remapped	O
sectors	O
may	O
continue	O
to	O
be	O
used	O
,	O
though	O
performance	O
may	O
decrease	O
as	O
the	O
drive	O
must	O
physically	O
move	O
the	O
heads	O
to	O
the	O
remapped	O
sector	O
.	O
</s>
<s>
In	O
modern	O
HDDs	O
,	O
each	O
drive	O
ships	O
with	O
zero	O
user-visible	O
bad	B-Device
sectors	I-Device
,	O
and	O
any	O
bad/reallocated	O
sectors	O
may	O
predict	O
the	O
impending	O
failure	O
of	O
a	O
drive	O
.	O
</s>
<s>
Head	O
crash	O
:	O
a	O
head	O
may	O
contact	O
the	O
rotating	O
platter	B-Device
due	O
to	O
mechanical	O
shock	O
or	O
other	O
reason	O
.	O
</s>
<s>
At	O
best	O
this	O
will	O
cause	O
irreversible	O
damage	O
and	O
data	B-General_Concept
loss	I-General_Concept
where	O
contact	O
was	O
made	O
.	O
</s>
<s>
Bad	B-Device
sectors	I-Device
:	O
some	O
magnetic	O
sectors	O
may	O
become	O
faulty	O
without	O
rendering	O
the	O
whole	O
drive	O
unusable	O
.	O
</s>
<s>
Stiction	O
:	O
after	O
a	O
time	O
the	O
head	O
may	O
not	O
"	O
take	O
off	O
"	O
when	O
started	O
up	O
as	O
it	O
tends	O
to	O
stick	O
to	O
the	O
platter	B-Device
,	O
a	O
phenomenon	O
known	O
as	O
stiction	O
.	O
</s>
<s>
This	O
is	O
usually	O
due	O
to	O
unsuitable	O
lubrication	O
properties	O
of	O
the	O
platter	B-Device
surface	O
,	O
a	O
design	O
or	O
manufacturing	O
defect	O
rather	O
than	O
wear	O
.	O
</s>
<s>
Since	O
modern	O
drives	O
use	O
fluid	O
dynamic	O
bearings	O
,	O
this	O
is	O
a	O
relatively	O
uncommon	O
reason	O
for	O
modern	O
hard	B-Device
drive	I-Device
failure	I-Device
.	O
</s>
<s>
Most	O
major	O
hard	B-Device
disk	I-Device
and	O
motherboard	O
vendors	O
support	O
S.M.A.R.T	O
,	O
which	O
measures	O
drive	O
characteristics	O
such	O
as	O
operating	O
temperature	O
,	O
spin-up	O
time	O
,	O
data	O
error	O
rates	O
,	O
etc	O
.	O
</s>
<s>
Certain	O
trends	O
and	O
sudden	O
changes	O
in	O
these	O
parameters	O
are	O
thought	O
to	O
be	O
associated	O
with	O
increased	O
likelihood	O
of	O
drive	O
failure	O
and	O
data	B-General_Concept
loss	I-General_Concept
.	O
</s>
<s>
A	O
2007	O
study	O
published	O
by	O
Google	B-Application
suggested	O
very	O
little	O
correlation	O
between	O
failure	O
rates	O
and	O
either	O
high	O
temperature	O
or	O
activity	O
level	O
.	O
</s>
<s>
Indeed	O
,	O
the	B-Application
Google	I-Application
study	O
indicated	O
that	O
"	O
one	O
of	O
our	O
key	O
findings	O
has	O
been	O
the	O
lack	O
of	O
a	O
consistent	O
pattern	O
of	O
higher	O
failure	O
rates	O
for	O
higher	O
temperature	O
drives	O
or	O
for	O
those	O
drives	O
at	O
higher	O
utilization	O
levels.	O
"	O
.	O
</s>
<s>
Hard	B-Device
drives	I-Device
with	O
S.M.A.R.T.-reported	O
average	O
temperatures	O
below	O
had	O
higher	O
failure	O
rates	O
than	O
hard	B-Device
drives	I-Device
with	O
the	O
highest	O
reported	O
average	O
temperature	O
of	O
,	O
failure	O
rates	O
at	O
least	O
twice	O
as	O
high	O
as	O
the	O
optimum	O
S.M.A.R.T.-reported	O
temperature	O
range	O
of	O
to	O
.	O
</s>
<s>
Statistics	O
in	O
this	O
matter	O
are	O
kept	O
highly	O
secret	O
by	O
most	O
entities	O
;	O
Google	B-Application
did	O
not	O
relate	O
manufacturers	O
 '	O
names	O
with	O
failure	O
rates	O
,	O
though	O
it	O
has	O
been	O
revealed	O
that	O
Google	B-Application
uses	O
Hitachi	O
Deskstar	O
drives	O
in	O
some	O
of	O
its	O
servers	O
.	O
</s>
<s>
Google	B-Application
's	I-Application
2007	O
study	O
found	O
,	O
based	O
on	O
a	O
large	O
field	O
sample	O
of	O
drives	O
,	O
that	O
actual	O
annualized	O
failure	O
rates	O
(	O
AFRs	O
)	O
for	O
individual	O
drives	O
ranged	O
from	O
1.7	O
%	O
for	O
first	O
year	O
drives	O
to	O
over	O
8.6	O
%	O
for	O
three-year-old	O
drives	O
.	O
</s>
<s>
A	O
similar	O
2007	O
study	O
at	O
CMU	O
on	O
enterprise	O
drives	O
showed	O
that	O
measured	O
MTBF	O
was	O
3	O
–	O
4	O
times	O
lower	O
than	O
the	O
manufacturer	O
's	O
specification	O
,	O
with	O
an	O
estimated	O
3%	O
mean	O
AFR	O
over	O
1	O
–	O
5	O
years	O
based	O
on	O
replacement	O
logs	O
for	O
a	O
large	O
sample	O
of	O
drives	O
,	O
and	O
that	O
hard	B-Device
drive	I-Device
failures	I-Device
were	O
highly	O
correlated	O
in	O
time	O
.	O
</s>
<s>
Background	O
scrubbing	B-Error_Name
was	O
found	O
to	O
be	O
effective	O
in	O
correcting	O
these	O
errors	O
.	O
</s>
<s>
SCSI	B-Architecture
,	O
SAS	O
,	O
and	O
FC	B-Architecture
drives	O
are	O
more	O
expensive	O
than	O
consumer-grade	O
SATA	O
drives	O
,	O
and	O
usually	O
used	O
in	O
servers	O
and	O
disk	B-General_Concept
arrays	I-General_Concept
,	O
where	O
SATA	O
drives	O
were	O
sold	O
to	O
the	O
home	O
computer	O
and	O
desktop	O
and	O
near-line	O
storage	O
market	O
and	O
were	O
perceived	O
to	O
be	O
less	O
reliable	O
.	O
</s>
<s>
The	O
mean	O
time	O
between	O
failures	O
(	O
MTBF	O
)	O
of	O
SATA	O
drives	O
is	O
usually	O
specified	O
to	O
be	O
about	O
1million	O
hours	O
(	O
some	O
drives	O
such	O
as	O
Western	B-Device
Digital	I-Device
Raptor	I-Device
have	O
rated	O
1.4million	O
hours	O
MTBF	O
)	O
,	O
while	O
SAS/FC	O
drives	O
are	O
rated	O
for	O
upwards	O
of	O
1.6million	O
hours	O
.	O
</s>
<s>
Both	O
AFR	O
and	O
MTBF	O
tend	O
to	O
measure	O
reliability	O
only	O
in	O
the	O
initial	O
part	O
of	O
the	O
life	O
of	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
thereby	O
understating	O
the	O
real	O
probability	O
of	O
failure	O
of	O
a	O
used	O
drive	O
.	O
</s>
<s>
The	O
cloud	O
storage	O
company	O
Backblaze	B-General_Concept
produces	O
an	O
annual	O
report	O
into	O
hard	B-Device
drive	I-Device
reliability	O
.	O
</s>
<s>
Consumer	O
drives	O
are	O
also	O
not	O
tested	O
to	O
work	O
with	O
enterprise	O
RAID	B-Architecture
cards	O
of	O
the	O
kind	O
used	O
in	O
a	O
datacenter	O
,	O
and	O
may	O
not	O
respond	O
in	O
the	O
time	O
a	O
RAID	B-Architecture
controller	O
expects	O
;	O
such	O
cards	O
will	O
be	O
identified	O
as	O
having	O
failed	O
when	O
they	O
have	O
not	O
.	O
</s>
<s>
Seagate	B-Device
ST3000DM001	I-Device
,	O
2012	O
ca	O
.	O
</s>
<s>
Data	O
from	O
a	O
failed	O
drive	O
can	O
sometimes	O
be	O
partially	O
or	O
totally	O
recovered	B-Application
if	O
the	O
platters	O
 '	O
magnetic	O
coating	O
is	O
not	O
totally	O
destroyed	O
.	O
</s>
<s>
Specialized	O
companies	O
carry	O
out	O
data	B-Application
recovery	I-Application
,	O
at	O
significant	O
cost	O
.	O
</s>
<s>
If	O
a	O
drive	O
is	O
started	O
up	O
once	O
it	O
may	O
continue	O
to	O
run	O
for	O
a	O
shorter	O
or	O
longer	O
time	O
but	O
never	O
start	O
again	O
,	O
so	O
as	O
much	O
data	O
as	O
possible	O
is	O
recovered	B-Application
as	O
soon	O
as	O
the	O
drive	O
starts	O
.	O
</s>
