<s>
In	O
computing	O
,	O
a	O
hybrid	B-Device
drive	I-Device
(	O
solid	B-Device
state	I-Device
hybrid	I-Device
drive	I-Device
–	O
SSHD	B-Device
)	O
is	O
a	O
logical	O
or	O
physical	O
storage	B-General_Concept
device	I-General_Concept
that	O
combines	O
a	O
faster	O
storage	B-General_Concept
medium	I-General_Concept
such	O
as	O
solid-state	B-Device
drive	I-Device
(	O
SSD	B-Device
)	O
with	O
a	O
higher-capacity	O
hard	B-Device
disk	I-Device
drive	I-Device
(	O
HDD	O
)	O
.	O
</s>
<s>
The	O
intent	O
is	O
adding	O
some	O
of	O
the	O
speed	O
of	O
SSDs	B-Device
to	O
the	O
cost-effective	O
storage	O
capacity	O
of	O
traditional	O
HDDs	O
.	O
</s>
<s>
The	O
purpose	O
of	O
the	O
SSD	B-Device
in	O
a	O
hybrid	B-Device
drive	I-Device
is	O
to	O
act	O
as	O
a	O
cache	O
for	O
the	O
data	O
stored	O
on	O
the	O
HDD	O
,	O
improving	O
the	O
overall	O
performance	O
by	O
keeping	O
copies	O
of	O
the	O
most	O
frequently	O
used	O
data	O
on	O
the	O
faster	O
SSD	B-Device
drive	I-Device
.	O
</s>
<s>
There	O
are	O
two	O
main	O
configurations	O
for	O
implementing	O
hybrid	B-Device
drives	I-Device
:	O
dual-drive	O
hybrid	O
systems	O
and	O
solid-state	B-Device
hybrid	I-Device
drives	I-Device
.	O
</s>
<s>
In	O
dual-drive	O
hybrid	O
systems	O
,	O
physically	O
separate	O
SSD	B-Device
and	O
HDD	O
devices	O
are	O
installed	O
in	O
the	O
same	O
computer	O
,	O
having	O
the	O
data	O
placement	O
optimization	O
performed	O
either	O
manually	O
by	O
the	O
end	O
user	O
,	O
or	O
automatically	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
through	O
the	O
creation	O
of	O
a	O
"	O
hybrid	O
"	O
logical	O
device	O
.	O
</s>
<s>
In	O
solid-state	B-Device
hybrid	I-Device
drives	I-Device
,	O
SSD	B-Device
and	O
HDD	O
functionalities	O
are	O
built	O
into	O
a	O
single	O
piece	O
of	O
hardware	O
,	O
where	O
data	O
placement	O
optimization	O
is	O
performed	O
either	O
entirely	O
by	O
the	O
device	O
(	O
self-optimized	O
mode	O
)	O
,	O
or	O
through	O
placement	O
"	O
hints	O
"	O
supplied	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
(	O
host-hinted	O
mode	O
)	O
.	O
</s>
<s>
There	O
are	O
two	O
main	O
"	O
hybrid	O
"	O
storage	O
technologies	O
that	O
combine	O
NAND	B-Device
flash	I-Device
memory	I-Device
or	O
SSDs	B-Device
,	O
with	O
the	O
HDD	O
technology	O
:	O
dual-drive	O
hybrid	O
systems	O
and	O
solid-state	B-Device
hybrid	I-Device
drives	I-Device
.	O
</s>
<s>
Dual-drive	O
hybrid	O
systems	O
combine	O
the	O
usage	O
of	O
separate	O
SSD	B-Device
and	O
HDD	O
devices	O
installed	O
in	O
the	O
same	O
computer	O
.	O
</s>
<s>
By	O
the	O
computer	O
's	O
operating	B-General_Concept
system	I-General_Concept
software	O
,	O
which	O
combines	O
SSD	B-Device
and	O
HDD	O
into	O
a	O
single	O
hybrid	O
volume	O
,	O
providing	O
an	O
easier	O
experience	O
to	O
the	O
end-user	O
.	O
</s>
<s>
Examples	O
of	O
hybrid	O
volumes	O
implementations	O
in	O
operating	B-General_Concept
systems	I-General_Concept
are	O
ZFS	O
 '	O
"	O
hybrid	O
storage	O
pools	O
"	O
,	O
bcache	B-Application
and	O
dm-cache	B-Application
on	O
Linux	B-Operating_System
,	O
Intel	O
's	O
Hystor	O
and	O
Apple	O
's	O
Fusion	B-Device
Drive	I-Device
,	O
and	O
other	O
Logical	B-Application
Volume	I-Application
Management	I-Application
based	O
implementations	O
on	O
OS	O
X	O
.	O
</s>
<s>
FCMs	O
combine	O
the	O
use	O
of	O
separate	O
SSD	B-Device
(	O
usually	O
an	O
mSATA	O
SSD	B-Device
module	O
)	O
and	O
HDD	O
components	O
,	O
while	O
managing	O
performance	O
optimizations	O
via	O
host	O
software	O
,	O
device	B-Application
drivers	I-Application
,	O
or	O
a	O
combination	O
of	O
both	O
.	O
</s>
<s>
One	O
example	O
is	O
Intel	B-Device
Smart	I-Device
Response	I-Device
Technology	I-Device
(	O
SRT	O
)	O
,	O
which	O
is	O
implemented	O
through	O
a	O
combination	O
of	O
certain	O
Intel	O
chipsets	O
and	O
Intel	O
storage	O
drivers	O
,	O
is	O
the	O
most	O
common	O
implementation	O
of	O
FCM	O
hybrid	O
systems	O
today	O
.	O
</s>
<s>
What	O
distinguished	O
this	O
dual-drive	O
system	O
from	O
an	O
SSHD	B-Device
system	O
is	O
that	O
each	O
drive	O
maintains	O
its	O
ability	O
to	O
be	O
addressed	O
independently	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
if	O
desired	O
.	O
</s>
<s>
Solid-state	O
hybrid	B-Device
drive	I-Device
(	O
also	O
known	O
by	O
the	O
initialism	O
SSHD	B-Device
)	O
refers	O
to	O
products	O
that	O
incorporate	O
a	O
significant	O
amount	O
of	O
NAND	B-Device
flash	I-Device
memory	I-Device
into	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
(	O
HDD	O
)	O
,	O
resulting	O
in	O
a	O
single	O
,	O
integrated	O
device	O
.	O
</s>
<s>
The	O
term	O
SSHD	B-Device
is	O
a	O
more	O
precise	O
term	O
than	O
the	O
more	O
general	O
hybrid	B-Device
drive	I-Device
,	O
which	O
has	O
previously	O
been	O
used	O
to	O
describe	O
SSHD	B-Device
devices	O
and	O
non-integrated	O
combinations	O
of	O
solid-state	B-Device
drives	I-Device
(	O
SSDs	B-Device
)	O
and	O
hard	B-Device
disk	I-Device
drives	I-Device
.	O
</s>
<s>
The	O
fundamental	O
design	O
principle	O
behind	O
SSHDs	B-Device
is	O
to	O
identify	O
data	O
elements	O
that	O
are	O
most	O
directly	O
associated	O
with	O
performance	O
(	O
frequently	O
accessed	O
data	O
,	O
boot	O
data	O
,	O
etc	O
.	O
)	O
</s>
<s>
and	O
store	O
these	O
data	O
elements	O
in	O
the	O
NAND	B-Device
flash	I-Device
memory	I-Device
.	O
</s>
<s>
An	O
example	O
of	O
an	O
often	O
confused	O
dual-drive	O
system	O
being	O
considered	O
an	O
SSHD	B-Device
is	O
the	O
use	O
of	O
laptops	O
which	O
combine	O
separate	O
SSD	B-Device
and	O
HDD	O
components	O
into	O
the	O
same	O
2.5-inch	O
HDD-size	O
unit	O
,	O
while	O
at	O
the	O
same	O
time	O
(	O
unlike	O
SSHDs	B-Device
)	O
keeping	O
these	O
two	O
components	O
visible	O
and	O
accessible	O
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
as	O
two	O
distinct	O
partitions	O
.	O
</s>
<s>
WD	O
's	O
Black2	O
drive	O
is	O
a	O
typical	O
example	O
;	O
the	O
drive	O
can	O
either	O
be	O
used	O
as	O
a	O
distinct	O
SSD	B-Device
and	O
HDD	O
by	O
partitioning	O
it	O
appropriately	O
,	O
or	O
software	O
can	O
be	O
used	O
to	O
automatically	O
manage	O
the	O
SSD	B-Device
portion	O
and	O
present	O
the	O
drive	O
to	O
the	O
user	O
as	O
a	O
single	O
large	O
volume	O
.	O
</s>
<s>
In	O
the	O
two	O
forms	O
of	O
hybrid	O
storage	O
technologies	O
(	O
dual-drive	O
hybrid	O
systems	O
and	O
SSHDs	B-Device
)	O
,	O
the	O
goal	O
is	O
to	O
combine	O
HDD	O
and	O
a	O
faster	O
technology	O
(	O
often	O
NAND	B-Device
flash	I-Device
memory	I-Device
)	O
to	O
provide	O
a	O
balance	O
of	O
improved	O
performance	O
and	O
high-capacity	O
storage	O
availability	O
.	O
</s>
<s>
Making	O
decisions	O
about	O
which	O
data	O
elements	O
are	O
prioritized	O
for	O
NAND	B-Device
flash	I-Device
memory	I-Device
is	O
at	O
the	O
core	O
of	O
SSHD	B-Device
technology	O
.	O
</s>
<s>
Products	O
offered	O
by	O
various	O
vendors	O
may	O
achieve	O
this	O
with	O
device	O
firmware	B-Application
,	O
device	B-Application
drivers	I-Application
or	O
software	O
modules	O
and	O
device	B-Application
drivers	I-Application
.	O
</s>
<s>
In	O
this	O
mode	O
of	O
operation	O
,	O
the	O
SSHD	B-Device
works	O
independently	O
from	O
the	O
host	O
operating	B-General_Concept
system	I-General_Concept
or	O
host	O
device	O
drives	O
to	O
make	O
all	O
decisions	O
related	O
to	O
identifying	O
data	O
that	O
will	O
be	O
stored	O
in	O
NAND	B-Device
flash	I-Device
memory	I-Device
.	O
</s>
<s>
This	O
mode	O
results	O
in	O
a	O
storage	O
product	O
that	O
appears	O
and	O
operates	O
to	O
a	O
host	O
system	O
exactly	O
as	O
a	O
traditional	O
hard	B-Device
drive	I-Device
would	O
.	O
</s>
<s>
In	O
this	O
mode	O
of	O
operation	O
,	O
the	O
SSHD	B-Device
enables	O
an	O
extended	O
set	O
of	O
SATA	O
commands	O
defined	O
in	O
the	O
so-called	O
Hybrid	O
Information	O
feature	O
,	O
introduced	O
in	O
version	O
3.2	O
of	O
the	O
Serial	O
ATA	O
International	O
Organization	O
(	O
SATA-IO	O
)	O
standards	O
for	O
the	O
SATA	O
interface	O
.	O
</s>
<s>
Using	O
these	O
SATA	O
commands	O
,	O
decisions	O
about	O
which	O
data	O
elements	O
are	O
placed	O
in	O
the	O
NAND	B-Device
flash	I-Device
memory	I-Device
come	O
from	O
the	O
host	O
operating	B-General_Concept
system	I-General_Concept
,	O
device	B-Application
drivers	I-Application
,	O
file	O
systems	O
,	O
or	O
a	O
combination	O
of	O
these	O
host-level	O
components	O
.	O
</s>
<s>
Some	O
of	O
the	O
specific	O
features	O
of	O
SSHD	B-Device
drives	O
,	O
such	O
as	O
the	O
host-hinted	O
mode	O
,	O
require	O
software	O
support	O
from	O
within	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Microsoft	O
added	O
support	O
for	O
the	O
host-hinted	O
operation	O
into	O
Windows	O
8.1	O
,	O
while	O
patches	O
for	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
are	O
available	O
since	O
October	O
2014	O
,	O
pending	O
their	O
inclusion	O
into	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
mainline	O
.	O
</s>
<s>
In	O
2007	O
,	O
Seagate	O
and	O
Samsung	O
introduced	O
the	O
first	O
hybrid	B-Device
drives	I-Device
with	O
the	O
Seagate	O
Momentus	O
PSD	O
and	O
Samsung	O
SpinPoint	O
MH80	O
products	O
.	O
</s>
<s>
Both	O
models	O
were	O
2.5-inch	O
drives	O
,	O
featuring	O
128MB	O
or	O
256MB	O
NAND	B-Device
flash	I-Device
memory	I-Device
options	O
.	O
</s>
<s>
Seagate	O
's	O
Momentus	O
PSD	O
emphasized	O
power	O
efficiency	O
for	O
a	O
better	O
mobile	O
experience	O
and	O
relied	O
on	O
Windows	B-Application
Vista	I-Application
's	O
ReadyDrive	O
.	O
</s>
<s>
In	O
May	O
2010	O
,	O
Seagate	O
introduced	O
a	O
new	O
hybrid	O
product	O
called	O
the	O
Momentus	O
XT	O
and	O
used	O
the	O
term	O
solid-state	O
hybrid	B-Device
drive	I-Device
.	O
</s>
<s>
This	O
product	O
focused	O
on	O
delivering	O
the	O
combined	O
benefits	O
of	O
hard	B-Device
drive	I-Device
capacity	I-Device
points	O
with	O
SSD-like	O
performance	O
.	O
</s>
<s>
It	O
shipped	O
as	O
a	O
500GB	O
HDD	O
with	O
4GB	O
of	O
integrated	O
NAND	B-Device
flash	I-Device
memory	I-Device
.	O
</s>
<s>
In	O
November	O
2011	O
,	O
Seagate	O
introduced	O
what	O
they	O
referred	O
to	O
as	O
their	O
second-generation	O
SSHD	B-Device
,	O
which	O
increased	O
the	O
capacity	O
to	O
750GB	O
and	O
pushed	O
the	O
integrated	O
NAND	B-Device
flash	I-Device
memory	I-Device
to	O
8GB	O
.	O
</s>
<s>
In	O
March	O
2012	O
,	O
Seagate	O
introduced	O
their	O
third-generation	O
laptop	O
SSHDs	B-Device
with	O
two	O
modelsa	O
500GB	O
and	O
1TB	O
,	O
both	O
with	O
8GB	O
of	O
integrated	O
NAND	B-Device
flash	I-Device
memory	I-Device
.	O
</s>
<s>
In	O
September	O
2012	O
,	O
Toshiba	O
announced	O
its	O
first	O
SSHD	B-Device
,	O
delivering	O
SSD-like	O
performance	O
and	O
responsiveness	O
by	O
combining	O
8GB	O
of	O
Toshiba	O
's	O
own	O
SLC	O
NAND	B-Device
flash	I-Device
memory	I-Device
and	O
innovative	O
,	O
self-learning	O
algorithms	O
with	O
up	O
to	O
1TB	O
of	O
storage	O
capacity	O
.	O
</s>
<s>
In	O
September	O
2012	O
,	O
Western	O
Digital	O
(	O
WD	O
)	O
announced	O
a	O
hybrid	O
technology	O
platform	O
pairing	O
cost-effective	O
MLC	O
NAND	B-Device
flash	I-Device
memory	I-Device
with	O
magnetic	O
disks	O
to	O
deliver	O
high-performance	O
,	O
large-capacity	O
integrated	O
storage	O
systems	O
.	O
</s>
<s>
In	O
November	O
2012	O
,	O
Apple	O
Inc	O
.	O
released	O
the	O
factory-configured	O
dual-drive	O
hybrid	O
system	O
named	O
Fusion	B-Device
Drive	I-Device
.	O
</s>
<s>
In	O
October	O
2015	O
,	O
TarDisk	O
introduced	O
the	O
plug-and-play	O
dual-drive	O
hybrid	O
system	O
"	O
TarDisk	O
Pear	O
"	O
,	O
with	O
flash	B-Device
memory	I-Device
size	O
options	O
up	O
to	O
256GB	O
.	O
</s>
<s>
Late	O
2011	O
and	O
early	O
2012	O
benchmarks	O
using	O
an	O
SSHD	B-Device
consisting	O
of	O
a	O
750GB	O
HDD	O
and	O
8GB	O
of	O
NAND	O
cache	O
found	O
that	O
SSHDs	B-Device
did	O
not	O
offer	O
SSD	B-Device
performance	O
on	O
random	O
read/write	O
and	O
sequential	O
read/write	O
,	O
but	O
were	O
faster	O
than	O
HDDs	O
for	O
application	O
startup	O
and	O
shutdown	O
.	O
</s>
<s>
The	O
2011	O
benchmark	O
included	O
loading	O
an	O
image	O
of	O
a	O
system	O
that	O
had	O
been	O
used	O
heavily	O
,	O
running	O
many	O
applications	O
,	O
to	O
bypass	O
the	O
performance	O
advantage	O
of	O
a	O
freshly-installed	O
system	O
;	O
it	O
found	O
in	O
real-world	O
tests	O
that	O
performance	O
was	O
much	O
closer	O
to	O
an	O
SSD	B-Device
than	O
to	O
a	O
mechanical	O
HDD	O
.	O
</s>
<s>
Different	O
benchmark	O
tests	O
found	O
the	O
SSHD	B-Device
to	O
be	O
between	O
an	O
HDD	O
and	O
SSD	B-Device
,	O
but	O
usually	O
significantly	O
slower	O
than	O
an	O
SSD	B-Device
.	O
</s>
<s>
In	O
the	O
case	O
of	O
uncached	O
random	O
access	O
performance	O
(	O
multiple	O
4KB	O
random	O
reads	O
and	O
writes	O
)	O
the	O
SSHD	B-Device
was	O
no	O
faster	O
than	O
a	O
comparable	O
HDD	O
;	O
there	O
is	O
advantage	O
only	O
with	O
data	O
that	O
is	O
cached	O
.	O
</s>
<s>
The	O
author	O
concluded	O
that	O
the	O
SSHD	B-Device
drive	O
was	O
the	O
best	O
non-SSD	O
type	O
of	O
drive	O
by	O
a	O
significant	O
margin	O
,	O
and	O
that	O
the	O
larger	O
the	O
solid-state	O
cache	O
,	O
the	O
better	O
the	O
performance	O
.	O
</s>
