<s>
Nearline	B-General_Concept
storage	I-General_Concept
(	O
a	O
portmanteau	O
of	O
"	O
near	O
"	O
and	O
"	O
online	B-General_Concept
storage	I-General_Concept
"	O
)	O
is	O
a	O
term	O
used	O
in	O
computer	O
science	O
to	O
describe	O
an	O
intermediate	O
type	O
of	O
data	O
storage	O
that	O
represents	O
a	O
compromise	O
between	O
online	B-General_Concept
storage	I-General_Concept
(	O
supporting	O
frequent	O
,	O
very	O
rapid	O
access	O
to	O
data	O
)	O
and	O
offline	O
storage/archiving	O
(	O
used	O
for	O
backups	O
or	O
long-term	O
storage	O
,	O
with	O
infrequent	O
access	O
to	O
data	O
)	O
.	O
</s>
<s>
Nearline	B-General_Concept
storage	I-General_Concept
dates	O
back	O
to	O
the	O
IBM	O
3850	O
Mass	O
Storage	B-General_Concept
System	I-General_Concept
(	O
MSS	O
)	O
tape	B-Device
library	I-Device
,	O
which	O
was	O
announced	O
in	O
1974	O
.	O
</s>
<s>
The	O
formal	O
distinction	O
between	O
online	O
,	O
nearline	B-General_Concept
,	O
and	O
offline	O
storage	O
is	O
:	O
</s>
<s>
Online	B-General_Concept
storage	I-General_Concept
is	O
immediately	O
available	O
for	O
input/output	O
(	O
I/O	O
)	O
.	O
</s>
<s>
Nearline	B-General_Concept
storage	I-General_Concept
is	O
not	O
immediately	O
available	O
,	O
but	O
can	O
be	O
made	O
online	O
quickly	O
without	O
human	O
intervention	O
.	O
</s>
<s>
For	O
example	O
,	O
always-on	O
spinning	O
hard	B-Device
disk	I-Device
drives	I-Device
are	O
online	B-General_Concept
storage	I-General_Concept
,	O
while	O
spinning	O
drives	O
that	O
spin	O
down	O
automatically	O
,	O
such	O
as	O
in	O
massive	O
arrays	O
of	O
idle	O
disks	O
(	O
MAID	O
)	O
,	O
are	O
nearline	B-General_Concept
storage	I-General_Concept
.	O
</s>
<s>
Removable	O
media	O
such	O
as	O
tape	O
cartridges	O
that	O
can	O
be	O
automatically	O
loaded	O
,	O
as	O
in	O
tape	B-Device
libraries	I-Device
,	O
are	O
nearline	B-General_Concept
storage	I-General_Concept
,	O
while	O
tape	O
cartridges	O
that	O
must	O
be	O
manually	O
loaded	O
are	O
offline	O
storage	O
.	O
</s>
<s>
The	O
nearline	B-General_Concept
storage	I-General_Concept
system	O
knows	O
on	O
which	O
volume	O
(	O
cartridge	O
)	O
the	O
data	O
resides	O
,	O
and	O
usually	O
asks	O
a	O
robot	O
to	O
retrieve	O
it	O
from	O
this	O
physical	O
location	O
(	O
usually	O
:	O
a	O
tape	B-Device
library	I-Device
or	O
optical	B-Device
jukebox	I-Device
)	O
and	O
put	O
it	O
into	O
a	O
tape	O
drive	O
or	O
optical	O
disc	O
drive	O
to	O
enable	O
access	O
by	O
bringing	O
the	O
data	O
it	O
contains	O
online	O
.	O
</s>
<s>
Nearline	B-General_Concept
tape	O
and	O
optical	O
storage	O
has	O
the	O
advantage	O
of	O
relatively	O
longer	O
lifespans	O
compared	O
to	O
spinning	O
hard	B-Device
drives	I-Device
,	O
simply	O
due	O
to	O
the	O
storage	O
media	O
being	O
idle	O
and	O
usually	O
stored	O
in	O
protected	O
dust-free	O
enclosures	O
when	O
not	O
in	O
use	O
.	O
</s>
<s>
MAID	O
(	O
massive	O
array	O
of	O
idle	O
drives	O
)	O
systems	O
archive	O
data	O
in	O
an	O
array	O
of	O
hard	B-Device
disk	I-Device
drives	I-Device
,	O
with	O
most	O
drives	O
in	O
a	O
MAID	O
usually	O
stopped	O
.	O
</s>
<s>
For	O
a	O
given	O
amount	O
of	O
storage	B-General_Concept
capacity	I-General_Concept
,	O
MAID	O
systems	O
have	O
higher	O
densities	O
and	O
lower	O
power	O
and	O
cooling	O
requirements	O
than	O
"	O
hot	O
"	O
storage	B-General_Concept
systems	I-General_Concept
that	O
keep	O
all	O
the	O
disks	O
spinning	O
at	O
full	O
speed	O
at	O
all	O
times	O
.	O
</s>
<s>
Some	O
hard	B-Device
drive	I-Device
and	O
storage	B-General_Concept
systems	I-General_Concept
vendors	O
and	O
suppliers	O
use	O
the	O
term	O
in	O
reference	O
to	O
low-rotational	O
speed	O
hard	B-Device
drives	I-Device
that	O
are	O
built	O
to	O
be	O
more	O
reliable	O
than	O
generic	O
desktop	O
and	O
laptop	O
computer	O
hard	B-Device
drives	I-Device
.	O
</s>
<s>
Nearline	B-General_Concept
hard	B-Device
drives	I-Device
may	O
be	O
used	O
in	O
personal	O
or	O
small	O
business	O
network-attached	B-Application
storage	I-Application
(	O
NAS	B-Application
)	O
systems	O
,	O
or	O
as	O
non-critical	O
moderate-performance	O
data	O
storage	O
on	O
servers	O
,	O
where	O
greater	O
durability	O
is	O
required	O
for	O
the	O
drive	O
to	O
operate	O
continuously	O
.	O
</s>
<s>
By	O
comparison	O
,	O
standard	O
hard	B-Device
drives	I-Device
are	O
assumed	O
to	O
only	O
be	O
in	O
operation	O
for	O
a	O
few	O
hours	O
each	O
day	O
,	O
and	O
are	O
not	O
spinning	O
when	O
the	O
computer	O
is	O
either	O
turned	O
off	O
or	O
in	O
sleep	O
mode	O
.	O
</s>
<s>
Standard	O
hard	B-Device
drives	I-Device
may	O
also	O
use	O
data	O
caching	O
methods	O
that	O
can	O
improve	O
single-drive	O
performance	O
,	O
but	O
would	O
interfere	O
with	O
the	O
operation	O
of	O
multi-drive	O
RAID	B-Architecture
storage	I-Architecture
systems	O
,	O
potentially	O
causing	O
data	O
loss	O
or	O
corruption	O
.	O
</s>
<s>
Specifically	O
the	O
term	O
nearline	B-General_Concept
hard	B-Device
drive	I-Device
is	O
being	O
used	O
to	O
refer	O
to	O
high-capacity	O
Serial	O
ATA	O
drives	O
that	O
work	O
with	O
Serial	O
Attached	O
SCSI	O
storage	O
devices	O
.	O
</s>
