<s>
A	O
disk	B-Device
array	I-Device
controller	I-Device
is	O
a	O
device	O
that	O
manages	O
the	O
physical	O
disk	B-Device
drives	I-Device
and	O
presents	O
them	O
to	O
the	O
computer	O
as	O
logical	O
units	O
.	O
</s>
<s>
It	O
almost	O
always	O
implements	O
hardware	O
RAID	B-Architecture
,	O
thus	O
it	O
is	O
sometimes	O
referred	O
to	O
as	O
RAID	B-Device
controller	I-Device
.	O
</s>
<s>
It	O
also	O
often	O
provides	O
additional	O
disk	B-Device
cache	B-General_Concept
.	O
</s>
<s>
Disk	B-Device
array	I-Device
controller	I-Device
is	O
often	O
improperly	O
shortened	O
to	O
disk	B-General_Concept
controller	I-General_Concept
.	O
</s>
<s>
A	O
disk	B-Device
array	I-Device
controller	I-Device
provides	O
front-end	O
interfaces	O
and	O
back-end	O
interfaces	O
.	O
</s>
<s>
Back-end	O
interface	O
communicates	O
with	O
controlled	O
disks	B-Device
.	O
</s>
<s>
Hence	O
protocol	O
is	O
usually	O
ATA	B-Protocol
(	O
a.k.a.	O
</s>
<s>
PATA	B-Protocol
)	O
,	O
SATA	O
,	O
SCSI	B-Architecture
,	O
FC	B-Architecture
or	O
SAS	O
.	O
</s>
<s>
Front-end	O
interface	O
communicates	O
with	O
a	O
computer	O
's	O
host	B-Architecture
adapter	I-Architecture
(	O
HBA	O
,	O
Host	B-Architecture
Bus	I-Architecture
Adapter	I-Architecture
)	O
and	O
uses	O
:	O
</s>
<s>
Many	O
enterprise	O
controllers	O
use	O
FC	B-Architecture
on	O
front-end	O
and	O
SATA	O
on	O
back-end	O
.	O
</s>
<s>
In	O
a	O
modern	O
enterprise	O
architecture	O
disk	B-Device
array	I-Device
controllers	I-Device
(	O
sometimes	O
also	O
called	O
storage	O
processors	O
,	O
or	O
SPs	O
)	O
are	O
parts	O
of	O
physically	O
independent	O
enclosures	O
,	O
such	O
as	O
disk	B-General_Concept
arrays	I-General_Concept
placed	O
in	O
a	O
storage	O
area	O
network	O
(	O
SAN	O
)	O
or	O
network-attached	B-Application
storage	I-Application
(	O
NAS	B-Application
)	O
servers	O
.	O
</s>
<s>
Those	O
external	O
disk	B-General_Concept
arrays	I-General_Concept
are	O
usually	O
purchased	O
as	O
an	O
integrated	O
subsystem	O
of	O
RAID	B-Device
controllers	I-Device
,	O
disk	B-Device
drives	I-Device
,	O
power	O
supplies	O
,	O
and	O
management	O
software	O
.	O
</s>
<s>
Replication	B-General_Concept
with	O
a	O
remote	O
controller	O
....	O
</s>
<s>
A	O
simple	O
disk	B-Device
array	I-Device
controller	I-Device
may	O
fit	O
inside	O
a	O
computer	O
,	O
either	O
as	O
a	O
PCI	B-Protocol
expansion	B-Device
card	I-Device
or	O
just	O
built	O
onto	O
a	O
motherboard	B-Device
.	O
</s>
<s>
Such	O
a	O
controller	O
usually	O
provides	O
host	B-Architecture
bus	I-Architecture
adapter	I-Architecture
(	O
HBA	O
)	O
functionality	O
itself	O
to	O
save	O
physical	O
space	O
.	O
</s>
<s>
Hence	O
it	O
is	O
sometimes	O
called	O
a	O
RAID	B-Architecture
adapter	O
.	O
</s>
<s>
Intel	O
started	O
integrating	O
their	O
own	O
Matrix	B-Application
RAID	I-Application
controller	I-Application
in	O
their	O
more	O
upmarket	O
motherboards	B-Device
,	O
giving	O
control	O
over	O
4	O
devices	O
and	O
an	O
additional	O
2	O
SATA	O
connectors	O
,	O
and	O
totalling	O
6	O
SATA	O
connections	O
(	O
3Gbit/s	O
each	O
)	O
.	O
</s>
<s>
For	O
backward	O
compatibility	O
one	O
IDE	O
connector	O
able	O
to	O
connect	O
2	O
ATA	B-Protocol
devices	O
(	O
100	O
Mbit/s	O
)	O
is	O
also	O
present	O
.	O
</s>
<s>
While	O
hardware	O
RAID	B-Device
controllers	I-Device
were	O
available	O
for	O
a	O
long	O
time	O
,	O
they	O
always	O
required	O
expensive	O
SCSI	B-Architecture
hard	O
drives	O
and	O
aimed	O
at	O
the	O
server	B-Application
and	O
high-end	O
computing	O
market	O
.	O
</s>
<s>
SCSI	B-Architecture
technology	O
advantages	O
include	O
allowing	O
up	O
to	O
15	O
devices	O
on	O
one	O
bus	O
,	O
independent	O
data	O
transfers	O
,	O
hot-swapping	B-Device
,	O
much	O
higher	O
MTBF	O
.	O
</s>
<s>
Around	O
1997	O
,	O
with	O
the	O
introduction	O
of	O
ATAPI-4	O
(	O
and	O
thus	O
the	O
Ultra-DMA-Mode	B-General_Concept
0	I-General_Concept
,	O
which	O
enabled	O
fast	O
data-transfers	O
with	O
less	O
CPU	B-Device
utilization	O
)	O
the	O
first	O
ATA	B-Device
RAID	I-Device
controllers	O
were	O
introduced	O
as	O
PCI	B-Protocol
expansion	B-Device
cards	I-Device
.	O
</s>
<s>
Those	O
RAID	B-Architecture
systems	O
made	O
their	O
way	O
to	O
the	O
consumer	O
market	O
,	O
where	O
the	O
users	O
wanted	O
the	O
fault-tolerance	O
of	O
RAID	B-Architecture
without	O
investing	O
in	O
expensive	O
SCSI	B-Architecture
drives	O
.	O
</s>
<s>
ATA	B-Protocol
drives	I-Protocol
make	O
it	O
possible	O
to	O
build	O
RAID	B-Architecture
systems	O
at	O
lower	O
cost	O
than	O
with	O
SCSI	B-Architecture
,	O
but	O
most	O
ATA	B-Device
RAID	I-Device
controllers	O
lack	O
a	O
dedicated	O
buffer	O
or	O
high-performance	O
XOR	O
hardware	O
for	O
parity	O
calculation	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
ATA	B-Device
RAID	I-Device
performs	O
relatively	O
poorly	O
compared	O
to	O
most	O
SCSI	B-Architecture
RAID	B-Device
controllers	I-Device
.	O
</s>
<s>
Because	O
the	O
hardware	O
RAID	B-Device
controllers	I-Device
present	O
assembled	O
RAID	B-Architecture
volumes	O
,	O
operating	B-General_Concept
systems	I-General_Concept
are	O
n't	O
strictly	O
required	O
to	O
implement	O
the	O
complete	O
configuration	O
and	O
assembly	O
for	O
each	O
controller	O
.	O
</s>
<s>
Very	O
often	O
only	O
the	O
basic	O
features	O
are	O
implemented	O
in	O
the	O
open-source	B-Application
software	I-Application
driver	O
,	O
with	O
extended	O
features	O
being	O
provided	O
through	O
binary	O
blobs	O
directly	O
by	O
the	O
hardware	O
manufacturer	O
.	O
</s>
<s>
Normally	O
,	O
RAID	B-Device
controllers	I-Device
can	O
be	O
fully	O
configured	O
through	O
card	O
BIOS	B-Operating_System
before	O
an	O
operating	B-General_Concept
system	I-General_Concept
is	O
booted	O
,	O
and	O
after	O
the	O
operating	B-General_Concept
system	I-General_Concept
is	O
booted	O
,	O
proprietary	B-Application
configuration	O
utilities	O
are	O
available	O
from	O
the	O
manufacturer	O
of	O
each	O
controller	O
,	O
because	O
the	O
exact	O
feature	O
set	O
of	O
each	O
controller	O
may	O
be	O
specific	O
to	O
each	O
manufacturer	O
and	O
product	O
.	O
</s>
<s>
Unlike	O
the	O
network	B-Protocol
interface	I-Protocol
controllers	I-Protocol
for	O
Ethernet	O
,	O
which	O
can	O
be	O
usually	O
be	O
configured	O
and	O
serviced	O
entirely	O
through	O
the	O
common	O
operating	B-General_Concept
system	I-General_Concept
paradigms	O
like	O
ifconfig	B-Protocol
in	O
Unix	B-Application
,	O
without	O
a	O
need	O
for	O
any	O
third-party	O
tools	O
,	O
each	O
manufacturer	O
of	O
each	O
RAID	B-Device
controller	I-Device
usually	O
provides	O
their	O
own	O
proprietary	B-Application
software	I-Application
tooling	O
for	O
each	O
operating	B-General_Concept
system	I-General_Concept
that	O
they	O
deem	O
to	O
support	O
,	O
ensuring	O
a	O
vendor	O
lock-in	O
,	O
and	O
contributing	O
to	O
reliability	O
issues	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
FreeBSD	B-Operating_System
,	O
in	O
order	O
to	O
access	O
the	O
configuration	O
of	O
Adaptec	O
RAID	B-Device
controllers	I-Device
,	O
users	O
are	O
required	O
to	O
enable	O
Linux	O
compatibility	O
layer	O
,	O
and	O
use	O
the	O
Linux	O
tooling	O
from	O
Adaptec	O
,	O
potentially	O
compromising	O
the	O
stability	O
,	O
reliability	O
and	O
security	O
of	O
their	O
setup	O
,	O
especially	O
when	O
taking	O
the	O
long	O
term	O
view	O
in	O
mind	O
.	O
</s>
<s>
However	O
,	O
this	O
greatly	O
depends	O
on	O
the	O
controller	O
,	O
and	O
whether	O
appropriate	O
hardware	O
documentation	O
is	O
available	O
in	O
order	O
to	O
write	O
a	O
driver	O
,	O
and	O
some	O
controllers	O
do	O
have	O
open-source	B-Application
versions	O
of	O
their	O
configuration	O
utilities	O
,	O
for	O
example	O
,	O
mfiutil	O
and	O
mptutil	O
is	O
available	O
for	O
FreeBSD	B-Operating_System
since	O
FreeBSD	B-Operating_System
8.0	O
(	O
2009	O
)	O
,	O
as	O
well	O
as	O
mpsutil/mprutil	O
since	O
2015	O
,	O
each	O
supporting	O
only	O
their	O
respective	O
device	O
drivers	O
,	O
this	O
latter	O
fact	O
contributing	O
to	O
code	O
bloat	O
.	O
</s>
<s>
Some	O
other	O
operating	B-General_Concept
systems	I-General_Concept
have	O
implemented	O
their	O
own	O
generic	O
frameworks	O
for	O
interfacing	O
with	O
any	O
RAID	B-Device
controller	I-Device
,	O
and	O
provide	O
tools	O
for	O
monitoring	O
RAID	B-Architecture
volume	O
status	O
,	O
as	O
well	O
as	O
facilitation	O
of	O
drive	O
identification	O
through	O
LED	O
blinking	O
,	O
alarm	O
management	O
,	O
hot	B-General_Concept
spare	I-General_Concept
disk	I-General_Concept
designations	O
and	O
from	O
within	O
the	O
operating	B-General_Concept
system	I-General_Concept
without	O
having	O
to	O
reboot	O
into	O
card	O
BIOS	B-Operating_System
.	O
</s>
<s>
For	O
example	O
,	O
this	O
was	O
the	O
approach	O
taken	O
by	O
OpenBSD	B-Operating_System
in	O
2005	O
with	O
its	O
bio(4 )	O
pseudo-device	B-Application
driver	O
and	O
the	O
bioctl	B-Device
utility	O
,	O
which	O
provide	O
volume	O
status	O
,	O
and	O
allow	O
LED/alarm/hotspare	O
control	O
,	O
as	O
well	O
as	O
the	O
sensors	O
(	O
including	O
the	O
drive	O
sensor	O
)	O
for	O
health	O
monitoring	O
;	O
this	O
approach	O
has	O
subsequently	O
been	O
adopted	O
and	O
extended	O
by	O
NetBSD	B-Device
in	O
2007	O
as	O
well	O
.	O
</s>
<s>
With	O
bioctl	B-Device
,	O
the	O
feature	O
set	O
is	O
intentionally	O
kept	O
to	O
a	O
minimum	O
,	O
so	O
that	O
each	O
controller	O
can	O
be	O
supported	O
by	O
the	O
tool	O
in	O
the	O
same	O
way	O
;	O
the	O
initial	O
configuration	O
of	O
the	O
controller	O
is	O
meant	O
to	O
be	O
performed	O
through	O
card	O
BIOS	B-Operating_System
,	O
but	O
after	O
the	O
initial	O
configuration	O
,	O
all	O
day-to-day	O
monitoring	O
and	O
repair	O
should	O
be	O
possible	O
with	O
unified	O
and	O
generic	O
tools	O
,	O
which	O
is	O
what	O
bioctl	B-Device
is	O
set	O
to	O
accomplish	O
.	O
</s>
