<s>
mdadm	B-Application
is	O
a	O
Linux	B-Operating_System
utility	O
used	O
to	O
manage	O
and	O
monitor	O
software	O
RAID	B-Architecture
devices	O
.	O
</s>
<s>
It	O
is	O
used	O
in	O
modern	O
Linux	B-Application
distributions	I-Application
in	O
place	O
of	O
older	O
software	O
RAID	B-Architecture
utilities	O
such	O
as	O
raidtools2	O
or	O
raidtools	O
.	O
</s>
<s>
mdadm	B-Application
is	O
free	B-Application
software	I-Application
originally	O
maintained	O
by	O
,	O
and	O
copyrighted	O
to	O
,	O
Neil	O
Brown	O
of	O
SUSE	O
,	O
and	O
licensed	O
under	O
the	O
terms	O
of	O
version2	O
or	O
later	O
of	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
.	O
</s>
<s>
The	O
name	O
is	O
derived	O
from	O
the	O
md	O
(	O
multiple	O
device	O
)	O
device	O
nodes	O
it	O
administers	O
or	O
manages	O
,	O
and	O
it	O
replaced	O
a	O
previous	O
utility	O
mdctl	B-Application
.	O
</s>
<s>
Linux	B-Application
software	I-Application
RAID	I-Application
configurations	O
can	O
include	O
anything	O
presented	O
to	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
as	O
a	O
block	O
device	O
.	O
</s>
<s>
This	O
includes	O
whole	O
hard	O
drives	O
(	O
for	O
example	O
,	O
)	O
,	O
and	O
their	O
partitions	B-Application
(	O
for	O
example	O
,	O
)	O
.	O
</s>
<s>
RAID	B-Architecture
0	O
Block-level	O
striping	B-General_Concept
.	O
</s>
<s>
RAID	B-Architecture
1	O
Mirror	O
.	O
</s>
<s>
RAID	B-Architecture
4	O
Like	O
RAID0	O
,	O
but	O
with	O
an	O
extra	O
device	O
for	O
the	O
parity	B-Error_Name
.	O
</s>
<s>
RAID	B-Architecture
5	O
Like	O
RAID4	O
,	O
but	O
with	O
the	O
parity	B-Error_Name
distributed	O
across	O
all	O
devices	O
.	O
</s>
<s>
RAID	B-Architecture
6	O
Like	O
RAID5	O
,	O
but	O
with	O
two	O
parity	B-Error_Name
segments	O
per	O
stripe	O
.	O
</s>
<s>
RAID	B-Architecture
10	O
Take	O
a	O
number	O
of	O
RAID1	O
mirrorsets	O
and	O
stripe	O
across	O
them	O
RAID0	O
style	O
.	O
</s>
<s>
RAID	B-Architecture
10	O
is	O
distinct	O
from	O
RAID	B-Architecture
0+1	O
,	O
which	O
consists	O
of	O
a	O
top-level	O
RAID1	O
mirror	O
composed	O
of	O
high-performance	O
RAID0	O
stripes	O
directly	O
across	O
the	O
physical	O
hard	O
disks	O
.	O
</s>
<s>
A	O
single-drive	O
failure	O
in	O
a	O
RAID10	O
configuration	O
results	O
in	O
one	O
of	O
the	O
lower-level	O
mirrors	O
entering	O
degraded	B-General_Concept
mode	I-General_Concept
,	O
but	O
the	O
top-level	O
stripe	O
performing	O
normally	O
(	O
except	O
for	O
the	O
performance	O
hit	O
)	O
.	O
</s>
<s>
A	O
single-drive	O
failure	O
in	O
a	O
RAID0+1	O
configuration	O
results	O
in	O
one	O
of	O
the	O
lower-level	O
stripes	O
completely	O
failing	O
,	O
and	O
the	O
top-level	O
mirror	O
entering	O
degraded	B-General_Concept
mode	I-General_Concept
.	O
</s>
<s>
Container	O
a	O
group	O
of	O
devices	O
managed	O
as	O
a	O
single	O
device	O
,	O
in	O
which	O
one	O
can	O
build	O
RAID	B-Architecture
systems	O
.	O
</s>
<s>
More	O
recent	O
kernels	B-Operating_System
have	O
support	O
for	O
names	O
such	O
as	O
.	O
</s>
<s>
Under	O
2.4.x	O
kernels	B-Operating_System
and	O
earlier	O
these	O
two	O
were	O
the	O
only	O
options	O
.	O
</s>
<s>
Both	O
of	O
them	O
are	O
non-partitionable	O
.	O
</s>
<s>
Since	O
2.6.x	O
kernels	B-Operating_System
,	O
a	O
new	O
type	O
of	O
MD	O
device	O
was	O
introduced	O
,	O
a	O
partitionable	B-Application
array	O
.	O
</s>
<s>
The	O
partitions	B-Application
were	O
identified	O
by	O
adding	O
,	O
where	O
is	O
the	O
partition	B-Application
number	O
;	O
thus	O
for	O
example	O
.	O
</s>
<s>
Since	O
version	O
2.6.28	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
mainline	O
,	O
non-partitionable	O
arrays	O
can	O
be	O
partitioned	O
,	O
the	O
partitions	B-Application
being	O
referred	O
to	O
in	O
the	O
same	O
way	O
as	O
for	O
partitionable	B-Application
arrays	O
for	O
example	O
,	O
.	O
</s>
<s>
Since	O
version	O
3.7	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
mainline	O
,	O
md	O
supports	O
TRIM	O
operations	O
for	O
the	O
underlying	O
solid-state	B-Device
drives	I-Device
(	O
SSDs	B-Device
)	O
,	O
for	O
linear	O
,	O
RAID0	O
,	O
RAID1	O
,	O
RAID5	O
and	O
RAID10	O
layouts	O
.	O
</s>
<s>
Since	O
support	O
for	O
MD	O
is	O
found	O
in	O
the	O
kernel	B-Operating_System
,	O
there	O
is	O
an	O
issue	O
with	O
using	O
it	O
before	O
the	O
kernel	B-Operating_System
is	O
running	O
.	O
</s>
<s>
Specifically	O
it	O
will	O
not	O
be	O
present	O
if	O
the	O
boot	O
loader	O
is	O
either	O
(	O
e	O
)	O
LiLo	B-Application
or	O
GRUB	B-Application
legacy	O
.	O
</s>
<s>
Although	O
normally	O
present	O
,	O
it	O
may	O
not	O
be	O
present	O
for	O
GRUB	B-Application
2	I-Application
.	O
</s>
<s>
With	O
more	O
recent	O
bootloaders	O
it	O
is	O
possible	O
to	O
load	O
the	O
MD	O
support	O
as	O
a	O
kernel	B-Operating_System
module	O
through	O
the	O
initramfs	B-Application
mechanism	O
.	O
</s>
<s>
This	O
approach	O
allows	O
the	O
filesystem	O
to	O
be	O
inside	O
any	O
RAID	B-Architecture
system	O
without	O
the	O
need	O
of	O
a	O
complex	O
manual	O
configuration	O
.	O
</s>
<s>
Besides	O
its	O
own	O
formats	O
for	O
RAID	B-Architecture
volumes	O
metadata	O
,	O
Linux	B-Application
software	I-Application
RAID	I-Application
also	O
supports	O
external	O
metadata	O
formats	O
,	O
since	O
version	O
2.6.27	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
and	O
version	O
3.0	O
of	O
the	O
userspace	O
utility	O
.	O
</s>
<s>
This	O
allows	O
Linux	B-Operating_System
to	O
use	O
various	O
firmware	O
-	O
or	O
driver-based	O
RAID	B-Architecture
volumes	O
,	O
also	O
known	O
as	O
"	O
fake	O
RAID	B-Architecture
"	O
.	O
</s>
<s>
DDF	O
(	O
Disk	B-General_Concept
Data	I-General_Concept
Format	I-General_Concept
)	O
,	O
an	O
industry	O
standard	O
defined	O
by	O
the	O
Storage	O
Networking	O
Industry	O
Association	O
for	O
increased	O
interoperability	O
.	O
</s>
<s>
Volume	O
metadata	O
format	O
used	O
by	O
the	O
Intel	O
Rapid	O
Storage	O
Technology(RST )	O
,	O
former	O
Intel	B-Application
Matrix	I-Application
RAID	I-Application
,	O
implemented	O
on	O
many	O
consumer-level	O
motherboards	O
.	O
</s>
<s>
mdmpd	B-Application
was	O
a	O
daemon	B-Operating_System
used	O
for	O
monitoring	O
MD	O
multipath	O
devices	O
up	O
to	O
Linux	O
kernel	O
2.6.10-rc1	O
,	O
developed	O
by	O
Red	O
Hat	O
as	O
part	O
of	O
the	O
mdadm	B-Application
package	O
.	O
</s>
<s>
The	O
program	O
was	O
used	O
to	O
monitor	O
multipath	O
(	O
RAID	B-Architecture
)	O
devices	O
,	O
and	O
is	O
usually	O
started	O
at	O
boot	O
time	O
as	O
a	O
service	O
,	O
and	O
afterwards	O
running	O
as	O
a	O
daemon	B-Operating_System
.	O
</s>
<s>
The	O
linux	B-Operating_System
kernel	B-Operating_System
implements	O
multipath	O
disk	O
access	O
via	O
the	O
software	O
RAID	B-Architecture
stack	O
known	O
as	O
the	O
md	O
(	O
Multiple	O
Devices	O
)	O
driver	O
.	O
</s>
<s>
The	O
kernel	B-Operating_System
portion	O
of	O
the	O
md	O
multipath	O
driver	O
only	O
handles	O
routing	O
I/O	O
requests	O
to	O
the	O
proper	O
device	O
and	O
handling	O
failures	O
on	O
the	O
active	O
path	O
.	O
</s>
<s>
That	O
's	O
what	O
this	O
daemon	B-Operating_System
does	O
.	O
</s>
<s>
Upon	O
startup	O
,	O
it	O
reads	O
the	O
current	O
state	O
of	O
the	O
md	O
raid	B-Architecture
arrays	O
,	O
saves	O
that	O
state	O
,	O
and	O
then	O
waits	O
for	O
the	O
kernel	B-Operating_System
to	O
tell	O
it	O
something	O
interesting	O
has	O
happened	O
.	O
</s>
<s>
Once	O
it	O
starts	O
working	O
again	O
,	O
the	O
daemon	B-Operating_System
will	O
then	O
add	O
the	O
path	O
back	O
into	O
the	O
multipath	O
md	O
device	O
it	O
was	O
originally	O
part	O
of	O
as	O
a	O
new	O
spare	O
path	O
.	O
</s>
<s>
Mdmpd	B-Application
requires	O
this	O
to	O
find	O
arrays	O
to	O
monitor	O
paths	O
on	O
,	O
to	O
get	O
notification	O
of	O
interesting	O
events	O
and	O
to	O
monitor	O
array	O
reconstruction	O
on	O
Monitor	O
mode	O
.	O
</s>
<s>
The	O
data	O
on	O
a	O
raid	B-Architecture
1	O
Volume	O
will	O
be	O
the	O
same	O
like	O
the	O
data	O
in	O
a	O
normal	O
Partition	B-Application
.	O
</s>
<s>
The	O
RAID	B-Architecture
Information	O
will	O
stored	O
in	O
the	O
last	O
128kB	O
of	O
the	O
Partition	B-Application
.	O
</s>
<s>
This	O
means	O
,	O
to	O
convert	O
a	O
RAID	B-Architecture
1	O
Volume	O
to	O
normal	O
data	O
Partition	B-Application
it	O
is	O
possible	O
to	O
decrease	O
the	O
Partition	B-Application
size	O
by	O
128kB	O
and	O
change	O
the	O
Partition	B-Application
ID	O
from	O
fd	O
to	O
83	O
(	O
for	O
linux	B-Operating_System
)	O
.	O
</s>
