<s>
The	O
most	O
widespread	O
standard	O
for	O
configuring	O
multiple	O
hard	B-Device
disk	I-Device
drives	I-Device
is	O
RAID	B-Architecture
(	O
Redundant	O
Array	O
of	O
Inexpensive/Independent	O
Disks	O
)	O
,	O
which	O
comes	O
in	O
a	O
number	O
of	O
standard	B-General_Concept
configurations	I-General_Concept
and	O
non-standard	B-General_Concept
configurations	I-General_Concept
.	O
</s>
<s>
Non-RAID	B-General_Concept
drive	I-General_Concept
architectures	I-General_Concept
also	O
exist	O
,	O
and	O
are	O
referred	O
to	O
by	O
acronyms	O
with	O
tongue-in-cheek	O
similarity	O
to	O
RAID	B-Architecture
:	O
</s>
<s>
JBOD	O
(	O
derived	O
from	O
"	O
just	O
a	O
bunch	O
of	O
disks	O
"	O
)	O
:	O
described	O
multiple	O
hard	B-Device
disk	I-Device
drives	I-Device
operated	O
as	O
individual	O
independent	O
hard	B-Device
disk	I-Device
drives	I-Device
.	O
</s>
<s>
SPAN	O
or	O
BIG	O
:	O
A	O
method	O
of	O
combining	O
the	O
free	O
space	O
on	O
multiple	O
hard	B-Device
disk	I-Device
drives	I-Device
from	O
"	O
JBoD	O
"	O
to	O
create	O
a	O
spanned	O
volume	O
.	O
</s>
<s>
A	O
SPAN	O
or	O
BIG	O
is	O
generally	O
a	O
spanned	O
volume	O
only	O
,	O
as	O
it	O
often	O
contains	O
mismatched	O
types	O
and	O
sizes	O
of	O
hard	B-Device
disk	I-Device
drives	I-Device
.	O
</s>
<s>
MAID	O
(	O
derived	O
from	O
"	O
massive	O
array	O
of	O
idle	O
drives	O
"	O
)	O
:	O
an	O
architecture	O
using	O
hundreds	O
to	O
thousands	O
of	O
hard	B-Device
disk	I-Device
drives	I-Device
for	O
providing	O
nearline	B-General_Concept
storage	I-General_Concept
of	O
data	O
,	O
primarily	O
designed	O
for	O
"	O
Write	O
Once	O
,	O
Read	O
Occasionally	O
"	O
(	O
WORO	O
)	O
applications	O
,	O
in	O
which	O
increased	O
storage	O
density	O
and	O
decreased	O
cost	O
are	O
traded	O
for	O
increased	O
latency	O
and	O
decreased	O
redundancy	O
.	O
</s>
<s>
JBOD	O
(	O
abbreviated	O
from	O
"	O
Just	O
a	O
Bunch	O
Of	O
Disks	O
"	O
/	O
"	O
Just	O
a	O
Bunch	O
Of	O
Drives	O
"	O
)	O
is	O
an	O
architecture	O
using	O
multiple	O
hard	B-Device
drives	I-Device
exposed	O
as	O
individual	O
devices	O
.	O
</s>
<s>
Hard	B-Device
drives	I-Device
may	O
be	O
treated	O
independently	O
or	O
may	O
be	O
combined	O
into	O
one	O
or	O
more	O
logical	O
volumes	O
using	O
a	O
volume	O
manager	O
like	O
LVM	B-Application
or	O
mdadm	B-Application
,	O
or	O
a	O
device-spanning	O
filesystem	O
like	O
btrfs	B-Operating_System
;	O
such	O
volumes	O
are	O
usually	O
called	O
"	O
spanned	O
"	O
or	O
"	O
linear	O
|	O
SPAN	O
|	O
BIG	O
"	O
.	O
</s>
<s>
A	O
spanned	O
volume	O
provides	O
no	O
redundancy	O
,	O
so	O
failure	O
of	O
a	O
single	O
hard	B-Device
drive	I-Device
amounts	O
to	O
failure	O
of	O
the	O
whole	O
logical	O
volume	O
.	O
</s>
<s>
Concatenation	O
or	O
spanning	O
of	O
drives	O
is	O
not	O
one	O
of	O
the	O
numbered	O
RAID	B-General_Concept
levels	I-General_Concept
,	O
but	O
it	O
is	O
a	O
popular	O
method	O
for	O
combining	O
multiple	O
physical	O
disk	O
drives	O
into	O
a	O
single	O
logical	O
disk	O
.	O
</s>
<s>
If	O
RAID	B-Architecture
0	O
were	O
used	O
,	O
then	O
disk	O
0	O
and	O
disk	O
2	O
would	O
be	O
truncated	O
to	O
28	O
blocks	O
,	O
the	O
size	O
of	O
the	O
smallest	O
disk	O
in	O
the	O
array	O
(	O
disk	O
1	O
)	O
for	O
a	O
total	O
size	O
of	O
84	O
blocks	O
.	O
</s>
<s>
What	O
makes	O
a	O
SPAN	O
or	O
BIG	O
different	O
from	O
RAID	B-Architecture
configurations	O
is	O
the	O
possibility	O
for	O
the	O
selection	O
of	O
drives	O
.	O
</s>
<s>
While	O
RAID	B-Architecture
usually	O
requires	O
all	O
drives	O
to	O
be	O
of	O
similar	O
capacity	O
and	O
it	O
is	O
preferred	O
that	O
the	O
same	O
or	O
similar	O
drive	O
models	O
are	O
used	O
for	O
performance	O
reasons	O
,	O
a	O
spanned	O
volume	O
does	O
not	O
have	O
such	O
requirements	O
.	O
</s>
<s>
The	O
initial	O
release	O
of	O
Microsoft	O
's	O
Windows	B-Application
Home	I-Application
Server	I-Application
employs	O
drive	O
extender	O
technology	O
,	O
whereby	O
an	O
array	O
of	O
independent	O
drives	O
are	O
combined	O
by	O
the	O
OS	O
to	O
form	O
a	O
single	O
pool	O
of	O
available	O
storage	O
.	O
</s>
<s>
This	O
feature	O
was	O
removed	O
from	O
Windows	B-Application
Home	I-Application
Server	I-Application
in	O
its	O
subsequent	O
major	O
release	O
.	O
</s>
<s>
The	O
btrfs	B-Operating_System
filesystem	O
can	O
span	O
multiple	O
devices	O
of	O
different	O
sizes	O
,	O
including	O
RAID	B-Architecture
0/1/10	O
configurations	O
,	O
storing	O
1	O
to	O
4	O
redundant	O
copies	O
of	O
both	O
data	O
and	O
metadata	O
.	O
</s>
<s>
(	O
A	O
flawed	O
RAID	B-Architecture
5/6	O
also	O
exists	O
,	O
but	O
can	O
result	O
in	O
data	O
loss	O
.	O
)	O
</s>
<s>
For	O
RAID	B-Architecture
1	O
,	O
the	O
devices	O
must	O
have	O
complementary	O
sizes	O
.	O
</s>
<s>
The	O
ZFS	B-Application
filesystem	O
can	O
likewise	O
pool	O
multiple	O
devices	O
of	O
different	O
sizes	O
and	O
implement	O
RAID	B-Architecture
,	O
though	O
it	O
is	O
less	O
flexible	O
,	O
requiring	O
the	O
creation	O
of	O
virtual	O
devices	O
of	O
fixed	O
size	O
on	O
each	O
device	O
before	O
pooling	O
.	O
</s>
<s>
MAID	O
(	O
abbreviated	O
from	O
"	O
massive	O
array	O
of	O
idle	O
drives	O
"	O
)	O
is	O
an	O
architecture	O
using	O
hundreds	O
to	O
thousands	O
of	O
hard	B-Device
drives	I-Device
for	O
providing	O
nearline	B-General_Concept
storage	I-General_Concept
of	O
data	O
.	O
</s>
<s>
Compared	O
to	O
RAID	B-Architecture
technology	O
,	O
MAID	O
has	O
increased	O
storage	O
density	O
,	O
and	O
decreased	O
cost	O
,	O
electrical	O
power	O
,	O
and	O
cooling	O
requirements	O
.	O
</s>
<s>
laptop	B-Device
drives	O
)	O
are	O
significantly	O
more	O
expensive	O
.	O
</s>
<s>
MAID	O
can	O
supplement	O
or	O
replace	O
tape	B-Device
libraries	I-Device
in	O
hierarchical	B-Application
storage	I-Application
management	I-Application
.	O
</s>
