<s>
Nested	B-General_Concept
RAID	I-General_Concept
levels	I-General_Concept
,	O
also	O
known	O
as	O
hybrid	B-Architecture
RAID	I-Architecture
,	O
combine	O
two	O
or	O
more	O
of	O
the	O
standard	B-General_Concept
RAID	I-General_Concept
levels	I-General_Concept
(	O
where	O
"	O
RAID	B-Architecture
"	O
stands	O
for	O
"	O
redundant	B-Architecture
array	I-Architecture
of	I-Architecture
independent	I-Architecture
disks	I-Architecture
"	O
)	O
to	O
gain	O
performance	O
,	O
additional	O
redundancy	O
or	O
both	O
,	O
as	O
a	O
result	O
of	O
combining	O
properties	O
of	O
different	O
standard	O
RAID	B-Architecture
layouts	O
.	O
</s>
<s>
Nested	B-General_Concept
RAID	I-General_Concept
levels	I-General_Concept
are	O
usually	O
numbered	O
using	O
a	O
series	O
of	O
numbers	O
,	O
where	O
the	O
most	O
commonly	O
used	O
levels	O
use	O
two	O
numbers	O
.	O
</s>
<s>
The	O
first	O
number	O
in	O
the	O
numeric	O
designation	O
denotes	O
the	O
lowest	O
RAID	B-Architecture
level	O
in	O
the	O
"	O
stack	O
"	O
,	O
while	O
the	O
rightmost	O
one	O
denotes	O
the	O
highest	O
layered	O
RAID	B-Architecture
level	O
;	O
for	O
example	O
,	O
RAID50	O
layers	O
the	O
data	O
striping	O
of	O
RAID	B-Architecture
0	O
on	O
top	O
of	O
the	O
distributed	O
parity	O
of	O
RAID	B-Architecture
5	O
.	O
</s>
<s>
Nested	B-General_Concept
RAID	I-General_Concept
levels	I-General_Concept
include	O
RAID01	O
,	O
RAID10	O
,	O
RAID100	O
,	O
RAID50	O
and	O
RAID60	O
,	O
which	O
all	O
combine	O
data	O
striping	O
with	O
other	O
RAID	B-Architecture
techniques	O
;	O
as	O
a	O
result	O
of	O
the	O
layering	O
scheme	O
,	O
RAID01	O
and	O
RAID10	O
represent	O
significantly	O
different	O
nested	B-General_Concept
RAID	I-General_Concept
levels	I-General_Concept
.	O
</s>
<s>
RAID	B-Architecture
01	O
,	O
also	O
called	O
RAID	B-Architecture
0+1	O
,	O
is	O
a	O
RAID	B-Architecture
level	O
using	O
a	O
mirror	O
of	O
stripes	O
,	O
achieving	O
both	O
replication	O
and	O
sharing	O
of	O
data	O
between	O
disks	O
.	O
</s>
<s>
RAID	B-Architecture
03	O
,	O
also	O
called	O
RAID	B-Architecture
0+3	O
and	O
sometimes	O
RAID	B-Architecture
53	O
,	O
is	O
similar	O
to	O
RAID01	O
with	O
the	O
exception	O
that	O
byte-level	O
striping	O
with	O
dedicated	O
parity	O
is	O
used	O
instead	O
of	O
mirroring	O
.	O
</s>
<s>
RAID	B-Architecture
10	O
,	O
also	O
called	O
RAID	B-Architecture
1+0	O
and	O
sometimes	O
RAID	B-Architecture
1&0	O
,	O
is	O
similar	O
to	O
RAID01	O
with	O
an	O
exception	O
that	O
the	O
two	O
used	O
standard	B-General_Concept
RAID	I-General_Concept
levels	I-General_Concept
are	O
layered	O
in	O
the	O
opposite	O
order	O
;	O
thus	O
,	O
RAID10	O
is	O
a	O
stripe	O
of	O
mirrors	O
.	O
</s>
<s>
RAID10	O
,	O
as	O
recognized	O
by	O
the	O
storage	O
industry	O
association	O
and	O
as	O
generally	O
implemented	O
by	O
RAID	B-Architecture
controllers	O
,	O
is	O
a	O
RAID0	O
array	O
of	O
mirrors	O
,	O
which	O
may	O
be	O
two	O
-	O
or	O
three-way	O
mirrors	O
,	O
and	O
requires	O
a	O
minimum	O
of	O
four	O
drives	O
.	O
</s>
<s>
According	O
to	O
manufacturer	O
specifications	O
and	O
official	O
independent	O
benchmarks	O
,	O
in	O
most	O
cases	O
RAID10	O
provides	O
better	O
throughput	O
and	O
latency	O
than	O
all	O
other	O
RAID	B-General_Concept
levels	I-General_Concept
except	O
RAID0	O
(	O
which	O
wins	O
in	O
throughput	O
)	O
.	O
</s>
<s>
Thus	O
,	O
it	O
is	O
the	O
preferable	O
RAID	B-Architecture
level	O
for	O
I/O	O
-intensive	O
applications	O
such	O
as	O
database	O
,	O
email	O
,	O
and	O
web	O
servers	O
,	O
as	O
well	O
as	O
for	O
any	O
other	O
use	O
requiring	O
high	O
disk	O
performance	O
.	O
</s>
<s>
RAID	B-Architecture
50	O
,	O
also	O
called	O
RAID	B-Architecture
5+0	O
,	O
combines	O
the	O
straight	O
block-level	O
striping	O
of	O
RAID0	O
with	O
the	O
distributed	O
parity	O
of	O
RAID5	O
.	O
</s>
<s>
One	O
drive	O
from	O
each	O
of	O
the	O
RAID5	O
sets	O
could	O
fail	O
without	O
loss	O
of	O
data	O
;	O
for	O
example	O
,	O
a	O
RAID50	O
configuration	O
including	O
three	O
RAID5	O
sets	O
can	O
tolerate	O
three	O
maximum	O
potential	O
simultaneous	O
drive	O
failures	O
(	O
but	O
only	O
one	O
per	O
RAID	B-Architecture
5	O
set	O
)	O
.	O
</s>
<s>
Because	O
the	O
reliability	O
of	O
the	O
system	O
depends	O
on	O
quick	O
replacement	O
of	O
the	O
bad	O
drive	O
so	O
the	O
array	O
can	O
rebuild	O
,	O
it	O
is	O
common	O
to	O
include	O
hot	B-General_Concept
spares	I-General_Concept
that	O
can	O
immediately	O
start	O
rebuilding	O
the	O
array	O
upon	O
failure	O
.	O
</s>
<s>
RAID50	O
improves	O
upon	O
the	O
performance	O
of	O
RAID5	O
particularly	O
during	O
writes	O
,	O
and	O
provides	O
better	O
fault	O
tolerance	O
than	O
a	O
single	O
RAID	B-Architecture
level	O
does	O
.	O
</s>
<s>
As	O
the	O
number	O
of	O
drives	O
in	O
a	O
RAID	B-Architecture
set	O
increases	O
,	O
and	O
the	O
capacity	O
of	O
the	O
drives	O
increase	O
,	O
this	O
impacts	O
the	O
fault-recovery	O
time	O
correspondingly	O
as	O
the	O
interval	O
for	O
rebuilding	O
the	O
RAID	B-Architecture
set	O
increases	O
.	O
</s>
<s>
RAID	B-Architecture
60	O
,	O
also	O
called	O
RAID	B-Architecture
6+0	O
,	O
combines	O
the	O
straight	O
block-level	O
striping	O
of	O
RAID0	O
with	O
the	O
distributed	O
double	O
parity	O
of	O
RAID6	O
,	O
resulting	O
in	O
a	O
RAID0	O
array	O
striped	O
across	O
RAID6	O
elements	O
.	O
</s>
<s>
RAID	B-Architecture
100	O
,	O
sometimes	O
also	O
called	O
RAID	B-Architecture
10+0	O
,	O
is	O
a	O
stripe	O
of	O
RAID10s	O
.	O
</s>
<s>
Being	O
"	O
striped	O
two	O
ways	O
"	O
,	O
RAID100	O
is	O
described	O
as	O
a	O
"	O
plaid	O
RAID	B-Architecture
"	O
.	O
</s>
<s>
The	O
following	O
table	O
provides	O
an	O
overview	O
of	O
some	O
considerations	O
for	O
nested	B-General_Concept
RAID	I-General_Concept
levels	I-General_Concept
.	O
</s>
<s>
It	O
is	O
sometimes	O
necessary	O
to	O
use	O
in	O
place	O
of	O
due	O
to	O
the	O
inherent	O
nature	O
of	O
the	O
configuration	O
(	O
of	O
use	O
in	O
RAID	B-Architecture
10	O
)	O
.	O
</s>
<s>
Fault	O
tolerance	O
uses	O
for	O
representation	O
,	O
in	O
place	O
of	O
,	O
in	O
certain	O
Nested	B-General_Concept
RAID	I-General_Concept
levels	I-General_Concept
(	O
see	O
below	O
for	O
fault	O
tolerance	O
calculation	O
)	O
.	O
</s>
<s>
Fault	O
tolerance	O
is	O
the	O
number	O
of	O
drive	O
failures	O
allowed	O
,	O
where	O
min	O
is	O
the	O
guaranteed	O
number	O
of	O
failures	O
the	O
RAID	B-Architecture
can	O
handle	O
and	O
max	O
is	O
the	O
maximum	O
possible	O
without	O
guaranteed	O
failure	O
.	O
</s>
