<s>
Write	B-Error_Name
amplification	I-Error_Name
(	O
WA	O
)	O
is	O
an	O
undesirable	O
phenomenon	O
associated	O
with	O
flash	B-Device
memory	I-Device
and	O
solid-state	B-Device
drives	I-Device
(	O
SSDs	B-Device
)	O
where	O
the	O
actual	O
amount	O
of	O
information	O
physically	O
written	O
to	O
the	O
storage	O
media	O
is	O
a	O
multiple	O
of	O
the	O
logical	O
amount	O
intended	O
to	O
be	O
written	O
.	O
</s>
<s>
Because	O
flash	B-Device
memory	I-Device
must	O
be	O
erased	O
before	O
it	O
can	O
be	O
rewritten	O
,	O
with	O
much	O
coarser	O
granularity	O
of	O
the	O
erase	O
operation	O
when	O
compared	O
to	O
the	O
write	O
operation	O
,	O
the	O
process	O
to	O
perform	O
these	O
operations	O
results	O
in	O
moving	O
(	O
or	O
rewriting	O
)	O
user	O
data	O
and	O
metadata	O
more	O
than	O
once	O
.	O
</s>
<s>
This	O
multiplying	O
effect	O
increases	O
the	O
number	O
of	O
writes	O
required	O
over	O
the	O
life	O
of	O
the	O
SSD	B-Device
,	O
which	O
shortens	O
the	O
time	O
it	O
can	O
operate	O
reliably	O
.	O
</s>
<s>
The	O
increased	O
writes	O
also	O
consume	O
bandwidth	O
to	O
the	O
flash	B-Device
memory	I-Device
,	O
which	O
reduces	O
write	O
performance	O
to	O
the	O
SSD	B-Device
.	O
</s>
<s>
Many	O
factors	O
will	O
affect	O
the	O
WA	O
of	O
an	O
SSD	B-Device
;	O
some	O
can	O
be	O
controlled	O
by	O
the	O
user	O
and	O
some	O
are	O
a	O
direct	O
result	O
of	O
the	O
data	O
written	O
to	O
and	O
usage	O
of	O
the	O
SSD	B-Device
.	O
</s>
<s>
Intel	O
and	O
SiliconSystems	O
(	O
acquired	O
by	O
Western	O
Digital	O
in	O
2009	O
)	O
used	O
the	O
term	O
write	B-Error_Name
amplification	I-Error_Name
in	O
their	O
papers	O
and	O
publications	O
in	O
2008	O
.	O
</s>
<s>
WA	O
is	O
typically	O
measured	O
by	O
the	O
ratio	O
of	O
writes	O
committed	O
to	O
the	O
flash	B-Device
memory	I-Device
to	O
the	O
writes	O
coming	O
from	O
the	O
host	O
system	O
.	O
</s>
<s>
Without	O
compression	B-General_Concept
,	O
WA	O
cannot	O
drop	O
below	O
one	O
.	O
</s>
<s>
Using	O
compression	B-General_Concept
,	O
SandForce	O
has	O
claimed	O
to	O
achieve	O
a	O
write	B-Error_Name
amplification	I-Error_Name
of	O
0.5	O
,	O
with	O
best-case	O
values	O
as	O
low	O
as	O
0.14	O
in	O
the	O
SF-2281	O
controller	O
.	O
</s>
<s>
Due	O
to	O
the	O
nature	O
of	O
flash	B-Device
memory	I-Device
's	O
operation	O
,	O
data	O
cannot	O
be	O
directly	O
overwritten	O
as	O
it	O
can	O
in	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
.	O
</s>
<s>
When	O
data	O
is	O
first	O
written	O
to	O
an	O
SSD	B-Device
,	O
the	O
cells	O
all	O
start	O
in	O
an	O
erased	O
state	O
so	O
data	O
can	O
be	O
written	O
directly	O
using	O
pages	O
at	O
a	O
time	O
(	O
in	O
size	O
)	O
.	O
</s>
<s>
The	O
SSD	B-Device
controller	I-Device
on	O
the	O
SSD	B-Device
,	O
which	O
manages	O
the	O
flash	B-Device
memory	I-Device
and	O
interfaces	B-Application
with	O
the	O
host	O
system	O
,	O
uses	O
a	O
logical-to-physical	O
mapping	O
system	O
known	O
as	O
logical	B-Device
block	I-Device
addressing	I-Device
(	O
LBA	O
)	O
that	O
is	O
part	O
of	O
the	O
flash	O
translation	O
layer	O
(	O
FTL	O
)	O
.	O
</s>
<s>
When	O
new	O
data	O
comes	O
in	O
replacing	O
older	O
data	O
already	O
written	O
,	O
the	O
SSD	B-Device
controller	I-Device
will	O
write	O
the	O
new	O
data	O
in	O
a	O
new	O
location	O
and	O
update	O
the	O
logical	O
mapping	O
to	O
point	O
to	O
the	O
new	O
physical	O
location	O
.	O
</s>
<s>
Flash	B-Device
memory	I-Device
can	O
be	O
programmed	O
and	O
erased	O
only	O
a	O
limited	O
number	O
of	O
times	O
.	O
</s>
<s>
This	O
is	O
often	O
referred	O
to	O
as	O
the	O
maximum	O
number	O
of	O
program/erase	O
cycles	O
(	O
P/Ecycles	O
)	O
it	O
can	O
sustain	O
over	O
the	O
life	O
of	O
the	O
flash	B-Device
memory	I-Device
.	O
</s>
<s>
,	O
multi-level	B-Device
cell	I-Device
(	O
MLC	B-Device
)	O
flash	O
is	O
designed	O
for	O
lower	O
cost	O
applications	O
and	O
has	O
a	O
greatly	O
reduced	O
cycle	O
count	O
of	O
typically	O
between	O
3,000	O
and	O
5,000	O
.	O
</s>
<s>
A	O
lower	O
write	B-Error_Name
amplification	I-Error_Name
is	O
more	O
desirable	O
,	O
as	O
it	O
corresponds	O
to	O
a	O
reduced	O
number	O
of	O
P/Ecycles	O
on	O
the	O
flash	B-Device
memory	I-Device
and	O
thereby	O
to	O
an	O
increased	O
SSD	B-Device
life	O
.	O
</s>
<s>
Write	B-Error_Name
amplification	I-Error_Name
was	O
always	O
present	O
in	O
SSDs	B-Device
before	O
the	O
term	O
was	O
defined	O
,	O
but	O
it	O
was	O
in	O
2008	O
that	O
both	O
Intel	O
and	O
SiliconSystems	O
started	O
using	O
the	O
term	O
in	O
their	O
papers	O
and	O
publications	O
.	O
</s>
<s>
All	O
SSDs	B-Device
have	O
a	O
write	B-Error_Name
amplification	I-Error_Name
value	O
and	O
it	O
is	O
based	O
on	O
both	O
what	O
is	O
currently	O
being	O
written	O
and	O
what	O
was	O
previously	O
written	O
to	O
the	O
SSD	B-Device
.	O
</s>
<s>
In	O
order	O
to	O
accurately	O
measure	O
the	O
value	O
for	O
a	O
specific	O
SSD	B-Device
,	O
the	O
selected	O
test	O
should	O
be	O
run	O
for	O
enough	O
time	O
to	O
ensure	O
the	O
drive	O
has	O
reached	O
a	O
steady	O
state	O
condition	O
.	O
</s>
<s>
A	O
simple	O
formula	O
to	O
calculate	O
the	O
write	B-Error_Name
amplification	I-Error_Name
of	O
an	O
SSD	B-Device
is	O
:	O
</s>
<s>
Many	O
factors	O
affect	O
the	O
write	B-Error_Name
amplification	I-Error_Name
of	O
an	O
SSD	B-Device
.	O
</s>
<s>
The	O
table	O
below	O
lists	O
the	O
primary	O
factors	O
and	O
how	O
they	O
affect	O
the	O
write	B-Error_Name
amplification	I-Error_Name
.	O
</s>
<s>
For	O
example	O
,	O
as	O
the	O
amount	O
of	O
over-provisioning	O
increases	O
,	O
the	O
write	B-Error_Name
amplification	I-Error_Name
decreases	O
(	O
inverse	O
relationship	O
)	O
.	O
</s>
<s>
+	O
Write	B-Error_Name
amplification	I-Error_Name
factors	O
Factor	O
Description	O
Type	O
Relationship*	O
Garbage	B-General_Concept
collection	I-General_Concept
The	O
efficiency	O
of	O
the	O
algorithm	O
used	O
to	O
pick	O
the	O
next	O
best	O
block	O
to	O
erase	O
and	O
rewrite	O
Variable	O
Inverse	O
(	O
good	O
)	O
Over-provisioning	O
The	O
percentage	O
of	O
physical	O
capacity	O
which	O
is	O
allocated	O
to	O
the	O
SSD	B-Device
controller	I-Device
Variable	O
Inverse	O
(	O
good	O
)	O
TRIM	O
command	O
for	O
SATA	O
or	O
UNMAP	O
for	O
SCSI	O
These	O
commands	O
must	O
be	O
sent	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
(	O
OS	O
)	O
which	O
tells	O
the	O
storage	O
device	O
which	O
pages	O
contain	O
invalid	O
data	O
.	O
</s>
<s>
SSDs	B-Device
receiving	O
these	O
commands	O
can	O
then	O
reclaim	O
the	O
blocks	O
containing	O
these	O
pages	O
as	O
free	O
space	O
when	O
they	O
are	O
erased	O
instead	O
of	O
copying	O
the	O
invalid	O
data	O
to	O
clean	O
pages	O
.	O
</s>
<s>
Toggle	O
Positive	O
(	O
good	O
)	O
Free	O
user	O
space	O
The	O
percentage	O
of	O
the	O
user	O
capacity	O
free	O
of	O
actual	O
user	O
data	O
;	O
requires	O
TRIM	O
,	O
otherwise	O
the	O
SSD	B-Device
gains	O
no	O
benefit	O
from	O
any	O
free	O
user	O
capacity	O
Variable	O
Inverse	O
(	O
good	O
)	O
Secure	O
erase	O
Erases	O
all	O
user	O
data	O
and	O
related	O
metadata	O
which	O
resets	O
the	O
SSD	B-Device
to	O
the	O
initial	O
out-of-box	O
performance	O
(	O
until	O
garbage	B-General_Concept
collection	I-General_Concept
resumes	O
)	O
Toggle	O
Positive	O
(	O
good	O
)	O
Wear	B-Application
leveling	I-Application
The	O
efficiency	O
of	O
the	O
algorithm	O
that	O
ensures	O
every	O
block	O
is	O
written	O
an	O
equal	O
number	O
of	O
times	O
to	O
all	O
other	O
blocks	O
as	O
evenly	O
as	O
possible	O
Variable	O
Direct	O
(	O
bad	O
)	O
Separating	O
static	O
and	O
dynamic	O
data	O
Grouping	O
data	O
based	O
on	O
how	O
often	O
it	O
tends	O
to	O
change	O
Toggle	O
Positive	O
(	O
good	O
)	O
Sequential	O
writes	O
In	O
theory	O
,	O
sequential	O
writes	O
have	O
less	O
write	B-Error_Name
amplification	I-Error_Name
,	O
but	O
other	O
factors	O
will	O
still	O
affect	O
the	O
real	O
situation	O
Toggle	O
Positive	O
(	O
good	O
)	O
Random	O
writes	O
Writing	O
non-sequential	O
data	O
and	O
smaller	O
data	O
sizes	O
will	O
have	O
greater	O
impact	O
on	O
write	B-Error_Name
amplification	I-Error_Name
Toggle	O
Negative	O
(	O
bad	O
)	O
Data	B-General_Concept
compression	I-General_Concept
which	O
includes	O
data	B-General_Concept
deduplication	I-General_Concept
Write	B-Error_Name
amplification	I-Error_Name
goes	O
down	O
and	O
SSD	B-Device
speed	O
goes	O
up	O
when	O
data	B-General_Concept
compression	I-General_Concept
and	O
deduplication	O
eliminates	O
more	O
redundant	O
data	O
.	O
</s>
<s>
Variable	O
Inverse	O
(	O
good	O
)	O
Using	O
MLC	B-Device
NAND	O
in	O
SLC	O
mode	O
This	O
writes	O
data	O
at	O
a	O
rate	O
of	O
one	O
bit	O
per	O
cell	O
instead	O
of	O
the	O
designed	O
number	O
of	O
bits	O
per	O
cell	O
(	O
normally	O
two	O
bits	O
per	O
cell	O
)	O
to	O
speed	O
up	O
reads	O
and	O
writes	O
.	O
</s>
<s>
If	O
capacity	O
limits	O
of	O
the	O
NAND	O
in	O
SLC	O
mode	O
are	O
approached	O
,	O
the	O
SSD	B-Device
must	O
rewrite	O
the	O
oldest	O
data	O
written	O
in	O
SLC	O
mode	O
into	O
MLC	B-Device
/	O
TLC	O
mode	O
to	O
allow	O
space	O
in	O
the	O
SLC	O
mode	O
NAND	O
to	O
be	O
erased	O
in	O
order	O
to	O
accept	O
more	O
data	O
.	O
</s>
<s>
However	O
,	O
this	O
approach	O
can	O
reduce	O
wear	O
by	O
keeping	O
frequently-changed	O
pages	O
in	O
SLC	O
mode	O
to	O
avoid	O
programming	O
these	O
changes	O
in	O
MLC	B-Device
/	O
TLC	O
mode	O
,	O
because	O
writing	O
in	O
MLC	B-Device
/	O
TLC	O
mode	O
does	O
more	O
damage	O
to	O
the	O
flash	O
than	O
writing	O
in	O
SLC	O
mode	O
.	O
</s>
<s>
Therefore	O
,	O
this	O
approach	O
drives	O
up	O
write	B-Error_Name
amplification	I-Error_Name
but	O
could	O
reduce	O
wear	O
when	O
writing	O
patterns	O
target	O
frequently-written	O
pages	O
.	O
</s>
<s>
However	O
,	O
sequential	O
-	O
and	O
random-write	O
patterns	O
will	O
aggravate	O
the	O
damage	O
because	O
there	O
are	O
no	O
or	O
few	O
frequently-written	O
pages	O
that	O
could	O
be	O
contained	O
in	O
the	O
SLC	O
area	O
,	O
forcing	O
old	O
data	O
to	O
need	O
to	O
be	O
constantly	O
be	O
rewritten	O
to	O
MLC	B-Device
/	O
TLC	O
from	O
the	O
SLC	O
area	O
.	O
</s>
<s>
Data	O
is	O
written	O
to	O
the	O
flash	B-Device
memory	I-Device
in	O
units	O
called	O
pages	O
(	O
made	O
up	O
of	O
multiple	O
cells	O
)	O
.	O
</s>
<s>
This	O
is	O
a	O
process	O
called	O
garbage	B-General_Concept
collection	I-General_Concept
(	O
GC	O
)	O
.	O
</s>
<s>
All	O
SSDs	B-Device
include	O
some	O
level	O
of	O
garbage	B-General_Concept
collection	I-General_Concept
,	O
but	O
they	O
may	O
differ	O
in	O
when	O
and	O
how	O
fast	O
they	O
perform	O
the	O
process	O
.	O
</s>
<s>
Garbage	B-General_Concept
collection	I-General_Concept
is	O
a	O
big	O
part	O
of	O
write	B-Error_Name
amplification	I-Error_Name
on	O
the	O
SSD	B-Device
.	O
</s>
<s>
Reads	O
do	O
not	O
require	O
an	O
erase	O
of	O
the	O
flash	B-Device
memory	I-Device
,	O
so	O
they	O
are	O
not	O
generally	O
associated	O
with	O
write	B-Error_Name
amplification	I-Error_Name
.	O
</s>
<s>
In	O
the	O
limited	O
chance	O
of	O
a	O
read	O
disturb	O
error	O
,	O
the	O
data	O
in	O
that	O
block	O
is	O
read	O
and	O
rewritten	O
,	O
but	O
this	O
would	O
not	O
have	O
any	O
material	O
impact	O
on	O
the	O
write	B-Error_Name
amplification	I-Error_Name
of	O
the	O
drive	O
.	O
</s>
<s>
The	O
process	O
of	O
garbage	B-General_Concept
collection	I-General_Concept
involves	O
reading	O
and	O
rewriting	O
data	O
to	O
the	O
flash	B-Device
memory	I-Device
.	O
</s>
<s>
Many	O
SSD	B-Device
controllers	I-Device
implement	O
background	O
garbage	B-General_Concept
collection	I-General_Concept
(	O
BGC	O
)	O
,	O
sometimes	O
called	O
idle	O
garbage	B-General_Concept
collection	I-General_Concept
or	O
idle-time	O
garbage	B-General_Concept
collection	I-General_Concept
(	O
ITGC	O
)	O
,	O
where	O
the	O
controller	O
uses	O
idle	O
time	O
to	O
consolidate	O
blocks	O
of	O
flash	B-Device
memory	I-Device
before	O
the	O
host	O
needs	O
to	O
write	O
new	O
data	O
.	O
</s>
<s>
The	O
result	O
is	O
that	O
the	O
soon-to-be-deleted	O
data	O
is	O
rewritten	O
to	O
another	O
location	O
in	O
the	O
flash	B-Device
memory	I-Device
,	O
increasing	O
the	O
write	B-Error_Name
amplification	I-Error_Name
.	O
</s>
<s>
In	O
some	O
of	O
the	O
SSDs	B-Device
from	O
OCZ	O
the	O
background	O
garbage	B-General_Concept
collection	I-General_Concept
clears	O
up	O
only	O
a	O
small	O
number	O
of	O
blocks	O
then	O
stops	O
,	O
thereby	O
limiting	O
the	O
amount	O
of	O
excessive	O
writes	O
.	O
</s>
<s>
Another	O
solution	O
is	O
to	O
have	O
an	O
efficient	O
garbage	B-General_Concept
collection	I-General_Concept
system	O
which	O
can	O
perform	O
the	O
necessary	O
moves	O
in	O
parallel	O
with	O
the	O
host	O
writes	O
.	O
</s>
<s>
This	O
solution	O
is	O
more	O
effective	O
in	O
high	O
write	O
environments	O
where	O
the	O
SSD	B-Device
is	O
rarely	O
idle	O
.	O
</s>
<s>
The	O
SandForce	O
SSD	B-Device
controllers	I-Device
and	O
the	O
systems	O
from	O
Violin	O
Memory	O
have	O
this	O
capability	O
.	O
</s>
<s>
In	O
2010	O
,	O
some	O
manufacturers	O
(	O
notably	O
Samsung	O
)	O
introduced	O
SSD	B-Device
controllers	I-Device
that	O
extended	O
the	O
concept	O
of	O
BGC	O
to	O
analyze	O
the	O
file	B-Application
system	I-Application
used	O
on	O
the	O
SSD	B-Device
,	O
to	O
identify	O
recently	O
deleted	O
files	O
and	O
unpartitioned	B-Application
space	I-Application
.	O
</s>
<s>
Samsung	O
claimed	O
that	O
this	O
would	O
ensure	O
that	O
even	O
systems	O
(	O
operating	B-General_Concept
systems	I-General_Concept
and	O
SATA	O
controller	O
hardware	O
)	O
which	O
do	O
not	O
support	O
TRIM	O
could	O
achieve	O
similar	O
performance	O
.	O
</s>
<s>
The	O
operation	O
of	O
the	O
Samsung	O
implementation	O
appeared	O
to	O
assume	O
and	O
require	O
an	O
NTFS	B-Application
file	I-Application
system	I-Application
.	O
</s>
<s>
It	O
is	O
not	O
clear	O
if	O
this	O
feature	O
is	O
still	O
available	O
in	O
currently	O
shipping	O
SSDs	B-Device
from	O
these	O
manufacturers	O
.	O
</s>
<s>
Systemic	O
data	O
corruption	O
has	O
been	O
reported	O
on	O
these	O
drives	O
if	O
they	O
are	O
not	O
formatted	O
properly	O
using	O
MBR	B-Device
and	O
NTFS	B-Application
.	O
</s>
<s>
TRIM	O
is	O
a	O
SATA	O
command	O
that	O
enables	O
the	O
operating	B-General_Concept
system	I-General_Concept
to	O
tell	O
an	O
SSD	B-Device
which	O
blocks	O
of	O
previously	O
saved	O
data	O
are	O
no	O
longer	O
needed	O
as	O
a	O
result	O
of	O
file	O
deletions	O
or	O
volume	O
formatting	O
.	O
</s>
<s>
When	O
an	O
LBA	O
is	O
replaced	O
by	O
the	O
OS	O
,	O
as	O
with	O
an	O
overwrite	O
of	O
a	O
file	O
,	O
the	O
SSD	B-Device
knows	O
that	O
the	O
original	O
LBA	O
can	O
be	O
marked	O
as	O
stale	O
or	O
invalid	O
and	O
it	O
will	O
not	O
save	O
those	O
blocks	O
during	O
garbage	B-General_Concept
collection	I-General_Concept
.	O
</s>
<s>
If	O
the	O
user	O
or	O
operating	B-General_Concept
system	I-General_Concept
erases	O
a	O
file	O
(	O
not	O
just	O
remove	O
parts	O
of	O
it	O
)	O
,	O
the	O
file	O
will	O
typically	O
be	O
marked	O
for	O
deletion	O
,	O
but	O
the	O
actual	O
contents	O
on	O
the	O
disk	O
are	O
never	O
actually	O
erased	O
.	O
</s>
<s>
Because	O
of	O
this	O
,	O
the	O
SSD	B-Device
does	O
not	O
know	O
that	O
it	O
can	O
erase	O
the	O
LBAs	O
previously	O
occupied	O
by	O
the	O
file	O
,	O
so	O
the	O
SSD	B-Device
will	O
keep	O
including	O
such	O
LBAs	O
in	O
the	O
garbage	B-General_Concept
collection	I-General_Concept
.	O
</s>
<s>
The	O
introduction	O
of	O
the	O
TRIM	O
command	O
resolves	O
this	O
problem	O
for	O
operating	B-General_Concept
systems	I-General_Concept
that	O
support	O
it	O
like	O
Windows	O
7	O
,	O
Mac	O
OS	O
(	O
latest	O
releases	O
of	O
Snow	O
Leopard	O
,	O
Lion	O
,	O
and	O
Mountain	O
Lion	O
,	O
patched	O
in	O
some	O
cases	O
)	O
,	O
FreeBSD	B-Operating_System
since	O
version	O
8.1	O
,	O
and	O
Linux	B-Application
since	O
version	O
2.6.33	O
of	O
the	O
Linux	B-Application
kernel	O
mainline	O
.	O
</s>
<s>
This	O
informs	O
the	O
SSD	B-Device
that	O
the	O
LBAs	O
in	O
use	O
can	O
be	O
erased	O
and	O
reused	O
.	O
</s>
<s>
This	O
reduces	O
the	O
LBAs	O
needing	O
to	O
be	O
moved	O
during	O
garbage	B-General_Concept
collection	I-General_Concept
.	O
</s>
<s>
The	O
result	O
is	O
the	O
SSD	B-Device
will	O
have	O
more	O
free	O
space	O
enabling	O
lower	O
write	B-Error_Name
amplification	I-Error_Name
and	O
higher	O
performance	O
.	O
</s>
<s>
The	O
TRIM	O
command	O
also	O
needs	O
the	O
support	O
of	O
the	O
SSD	B-Device
.	O
</s>
<s>
If	O
the	O
firmware	B-Application
in	O
the	O
SSD	B-Device
does	O
not	O
have	O
support	O
for	O
the	O
TRIM	O
command	O
,	O
the	O
LBAs	O
received	O
with	O
the	O
TRIM	O
command	O
will	O
not	O
be	O
marked	O
as	O
invalid	O
and	O
the	O
drive	O
will	O
continue	O
to	O
garbage	O
collect	O
the	O
data	O
assuming	O
it	O
is	O
still	O
valid	O
.	O
</s>
<s>
Only	O
when	O
the	O
OS	O
saves	O
new	O
data	O
into	O
those	O
LBAs	O
will	O
the	O
SSD	B-Device
know	O
to	O
mark	O
the	O
original	O
LBA	O
as	O
invalid	O
.	O
</s>
<s>
SSD	B-Device
Manufacturers	O
that	O
did	O
not	O
originally	O
build	O
TRIM	O
support	O
into	O
their	O
drives	O
can	O
either	O
offer	O
a	O
firmware	B-Application
upgrade	O
to	O
the	O
user	O
,	O
or	O
provide	O
a	O
separate	O
utility	O
that	O
extracts	O
the	O
information	O
on	O
the	O
invalid	O
data	O
from	O
the	O
OS	O
and	O
separately	O
TRIMs	O
the	O
SSD	B-Device
.	O
</s>
<s>
Just	O
because	O
an	O
SSD	B-Device
supports	O
the	O
TRIM	O
command	O
does	O
not	O
necessarily	O
mean	O
it	O
will	O
be	O
able	O
to	O
perform	O
at	O
top	O
speed	O
immediately	O
after	O
a	O
TRIM	O
command	O
.	O
</s>
<s>
The	O
space	O
which	O
is	O
freed	O
up	O
after	O
the	O
TRIM	O
command	O
may	O
be	O
at	O
random	O
locations	O
spread	O
throughout	O
the	O
SSD	B-Device
.	O
</s>
<s>
Even	O
after	O
the	O
OS	O
and	O
SSD	B-Device
are	O
configured	O
to	O
support	O
the	O
TRIM	O
command	O
,	O
other	O
conditions	O
might	O
prevent	O
any	O
benefit	O
from	O
TRIM	O
.	O
</s>
<s>
,	O
databases	O
and	O
RAID	O
systems	O
are	O
not	O
yet	O
TRIM-aware	O
and	O
consequently	O
will	O
not	O
know	O
how	O
to	O
pass	O
that	O
information	O
on	O
to	O
the	O
SSD	B-Device
.	O
</s>
<s>
In	O
those	O
cases	O
the	O
SSD	B-Device
will	O
continue	O
to	O
save	O
and	O
garbage	O
collect	O
those	O
blocks	O
until	O
the	O
OS	O
uses	O
those	O
LBAs	O
for	O
new	O
writes	O
.	O
</s>
<s>
The	O
actual	O
benefit	O
of	O
the	O
TRIM	O
command	O
depends	O
upon	O
the	O
free	O
user	O
space	O
on	O
the	O
SSD	B-Device
.	O
</s>
<s>
If	O
the	O
user	O
capacity	O
on	O
the	O
SSD	B-Device
was	O
100GB	O
and	O
the	O
user	O
actually	O
saved	O
95GB	O
of	O
data	O
to	O
the	O
drive	O
,	O
any	O
TRIM	O
operation	O
would	O
not	O
add	O
more	O
than	O
5GB	O
of	O
free	O
space	O
for	O
garbage	B-General_Concept
collection	I-General_Concept
and	O
wear	B-Application
leveling	I-Application
.	O
</s>
<s>
In	O
those	O
situations	O
,	O
increasing	O
the	O
amount	O
of	O
over-provisioning	O
by	O
5GB	O
would	O
allow	O
the	O
SSD	B-Device
to	O
have	O
more	O
consistent	O
performance	O
because	O
it	O
would	O
always	O
have	O
the	O
additional	O
5GB	O
of	O
additional	O
free	O
space	O
without	O
having	O
to	O
wait	O
for	O
the	O
TRIM	O
command	O
to	O
come	O
from	O
the	O
OS	O
.	O
</s>
<s>
Over-provisioning	O
(	O
sometimes	O
spelled	O
as	O
OP	O
,	O
over	O
provisioning	O
,	O
or	O
overprovisioning	O
)	O
is	O
the	O
difference	O
between	O
the	O
physical	O
capacity	O
of	O
the	O
flash	B-Device
memory	I-Device
and	O
the	O
logical	O
capacity	O
presented	O
through	O
the	O
operating	B-General_Concept
system	I-General_Concept
(	O
OS	O
)	O
as	O
available	O
for	O
the	O
user	O
.	O
</s>
<s>
During	O
the	O
garbage	B-General_Concept
collection	I-General_Concept
,	O
wear-leveling	B-Application
,	O
and	O
bad	O
block	O
mapping	O
operations	O
on	O
the	O
SSD	B-Device
,	O
the	O
additional	O
space	O
from	O
over-provisioning	O
helps	O
lower	O
the	O
write	B-Error_Name
amplification	I-Error_Name
when	O
the	O
controller	O
writes	O
to	O
the	O
flash	B-Device
memory	I-Device
.	O
</s>
<s>
Over-provisioning	O
region	O
is	O
also	O
used	O
for	O
storing	O
firmware	B-Application
data	O
like	O
FTL	O
tables	O
.	O
</s>
<s>
Both	O
HDD	O
and	O
SSD	B-Device
vendors	O
use	O
the	O
term	O
GB	O
to	O
represent	O
a	O
decimal	O
GB	O
or	O
1,000,000,000	O
(=	O
109	O
)	O
bytes	O
.	O
</s>
<s>
Like	O
most	O
other	O
electronic	O
storage	O
,	O
flash	B-Device
memory	I-Device
is	O
assembled	O
in	O
powers	O
of	O
two	O
,	O
so	O
calculating	O
the	O
physical	O
capacity	O
of	O
an	O
SSD	B-Device
would	O
be	O
based	O
on	O
1,073,741,824	O
(=	O
230	O
)	O
per	O
binary	O
GB	O
or	O
GiB	O
.	O
</s>
<s>
Therefore	O
,	O
a	O
128GB	O
SSD	B-Device
with	O
0%	O
additional	O
over-provisioning	O
would	O
provide	O
128,000,000,000	O
bytes	O
to	O
the	O
user	O
(	O
out	O
of	O
137,438,953,472	O
total	O
)	O
.	O
</s>
<s>
As	O
an	O
example	O
,	O
a	O
manufacturer	O
might	O
publish	O
a	O
specification	O
for	O
their	O
SSD	B-Device
at	O
100	O
,	O
120	O
or	O
128GB	O
based	O
on	O
128GB	O
of	O
possible	O
capacity	O
.	O
</s>
<s>
This	O
free	O
space	O
can	O
be	O
identified	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
using	O
the	O
TRIM	O
command	O
.	O
</s>
<s>
Alternatively	O
,	O
some	O
SSDs	B-Device
provide	O
a	O
utility	O
that	O
permits	O
the	O
end	O
user	O
to	O
select	O
additional	O
over-provisioning	O
.	O
</s>
<s>
Furthermore	O
,	O
if	O
any	O
SSD	B-Device
is	O
set	O
up	O
with	O
an	O
overall	O
partitioning	B-Application
layout	O
smaller	O
than	O
100%	O
of	O
the	O
available	O
space	O
,	O
that	O
unpartitioned	B-Application
space	I-Application
will	O
be	O
automatically	O
used	O
by	O
the	O
SSD	B-Device
as	O
over-provisioning	O
as	O
well	O
.	O
</s>
<s>
Yet	O
another	O
source	O
of	O
over-provisioning	O
is	O
operating	B-General_Concept
system	I-General_Concept
minimum	O
free	O
space	O
limits	O
;	O
some	O
operating	B-General_Concept
systems	I-General_Concept
maintain	O
a	O
certain	O
minimum	O
free	O
space	O
per	O
drive	O
,	O
particularly	O
on	O
the	O
boot	O
or	O
main	O
drive	O
.	O
</s>
<s>
If	O
this	O
additional	O
space	O
can	O
be	O
identified	O
by	O
the	O
SSD	B-Device
,	O
perhaps	O
through	O
continuous	O
usage	O
of	O
the	O
TRIM	O
command	O
,	O
then	O
this	O
acts	O
as	O
semi-permanent	O
over-provisioning	O
.	O
</s>
<s>
Over-provisioning	O
often	O
takes	O
away	O
from	O
user	O
capacity	O
,	O
either	O
temporarily	O
or	O
permanently	O
,	O
but	O
it	O
gives	O
back	O
reduced	O
write	B-Error_Name
amplification	I-Error_Name
,	O
increased	O
endurance	O
,	O
and	O
increased	O
performance	O
.	O
</s>
<s>
The	O
SSD	B-Device
controller	I-Device
will	O
use	O
free	O
blocks	O
on	O
the	O
SSD	B-Device
for	O
garbage	B-General_Concept
collection	I-General_Concept
and	O
wear	B-Application
leveling	I-Application
.	O
</s>
<s>
The	O
portion	O
of	O
the	O
user	O
capacity	O
which	O
is	O
free	O
from	O
user	O
data	O
(	O
either	O
already	O
TRIMed	O
or	O
never	O
written	O
in	O
the	O
first	O
place	O
)	O
will	O
look	O
the	O
same	O
as	O
over-provisioning	O
space	O
(	O
until	O
the	O
user	O
saves	O
new	O
data	O
to	O
the	O
SSD	B-Device
)	O
.	O
</s>
<s>
With	O
an	O
SSD	B-Device
without	O
integrated	O
encryption	O
,	O
this	O
command	O
will	O
put	O
the	O
drive	O
back	O
to	O
its	O
original	O
out-of-box	O
state	O
.	O
</s>
<s>
This	O
will	O
initially	O
restore	O
its	O
performance	O
to	O
the	O
highest	O
possible	O
level	O
and	O
the	O
best	O
(	O
lowest	O
number	O
)	O
possible	O
write	B-Error_Name
amplification	I-Error_Name
,	O
but	O
as	O
soon	O
as	O
the	O
drive	O
starts	O
garbage	O
collecting	O
again	O
the	O
performance	O
and	O
write	B-Error_Name
amplification	I-Error_Name
will	O
start	O
returning	O
to	O
the	O
former	O
levels	O
.	O
</s>
<s>
GParted	B-Application
and	O
Ubuntu	B-Operating_System
live	O
CDs	O
provide	O
a	O
bootable	O
Linux	B-Application
system	O
of	O
disk	O
utilities	O
including	O
secure	O
erase	O
.	O
</s>
<s>
If	O
a	O
particular	O
block	O
was	O
programmed	O
and	O
erased	O
repeatedly	O
without	O
writing	O
to	O
any	O
other	O
blocks	O
,	O
that	O
block	O
would	O
wear	O
out	O
before	O
all	O
the	O
other	O
blocks	O
–	O
thereby	O
prematurely	O
ending	O
the	O
life	O
of	O
the	O
SSD	B-Device
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
SSD	B-Device
controllers	I-Device
use	O
a	O
technique	O
called	O
wear	B-Application
leveling	I-Application
to	O
distribute	O
writes	O
as	O
evenly	O
as	O
possible	O
across	O
all	O
the	O
flash	O
blocks	O
in	O
the	O
SSD	B-Device
.	O
</s>
<s>
Each	O
time	O
data	O
are	O
relocated	O
without	O
being	O
changed	O
by	O
the	O
host	O
system	O
,	O
this	O
increases	O
the	O
write	B-Error_Name
amplification	I-Error_Name
and	O
thus	O
reduces	O
the	O
life	O
of	O
the	O
flash	B-Device
memory	I-Device
.	O
</s>
<s>
The	O
separation	O
of	O
static	O
(	O
cold	O
)	O
and	O
dynamic	O
(	O
hot	O
)	O
data	O
to	O
reduce	O
write	B-Error_Name
amplification	I-Error_Name
is	O
not	O
a	O
simple	O
process	O
for	O
the	O
SSD	B-Device
controller	I-Device
.	O
</s>
<s>
The	O
process	O
requires	O
the	O
SSD	B-Device
controller	I-Device
to	O
separate	O
the	O
LBAs	O
with	O
data	O
which	O
is	O
constantly	O
changing	O
and	O
requiring	O
rewriting	O
(	O
dynamic	O
data	O
)	O
from	O
the	O
LBAs	O
with	O
data	O
which	O
rarely	O
changes	O
and	O
does	O
not	O
require	O
any	O
rewrites	O
(	O
static	O
data	O
)	O
.	O
</s>
<s>
If	O
the	O
data	O
is	O
mixed	O
in	O
the	O
same	O
blocks	O
,	O
as	O
with	O
almost	O
all	O
systems	O
today	O
,	O
any	O
rewrites	O
will	O
require	O
the	O
SSD	B-Device
controller	I-Device
to	O
rewrite	O
both	O
the	O
dynamic	O
data	O
(	O
which	O
caused	O
the	O
rewrite	O
initially	O
)	O
and	O
static	O
data	O
(	O
which	O
did	O
not	O
require	O
any	O
rewrite	O
)	O
.	O
</s>
<s>
Any	O
garbage	B-General_Concept
collection	I-General_Concept
of	O
data	O
that	O
would	O
not	O
have	O
otherwise	O
required	O
moving	O
will	O
increase	O
write	B-Error_Name
amplification	I-Error_Name
.	O
</s>
<s>
Therefore	O
,	O
separating	O
the	O
data	O
will	O
enable	O
static	O
data	O
to	O
stay	O
at	O
rest	O
and	O
if	O
it	O
never	O
gets	O
rewritten	O
it	O
will	O
have	O
the	O
lowest	O
possible	O
write	B-Error_Name
amplification	I-Error_Name
for	O
that	O
data	O
.	O
</s>
<s>
The	O
drawback	O
to	O
this	O
process	O
is	O
that	O
somehow	O
the	O
SSD	B-Device
controller	I-Device
must	O
still	O
find	O
a	O
way	O
to	O
wear	O
level	O
the	O
static	O
data	O
because	O
those	O
blocks	O
that	O
never	O
change	O
will	O
not	O
get	O
a	O
chance	O
to	O
be	O
written	O
to	O
their	O
maximum	O
P/E	O
cycles	O
.	O
</s>
<s>
When	O
an	O
SSD	B-Device
is	O
writing	O
large	O
amounts	O
of	O
data	O
sequentially	O
,	O
the	O
write	B-Error_Name
amplification	I-Error_Name
is	O
equal	O
to	O
one	O
meaning	O
there	O
is	O
less	O
write	B-Error_Name
amplification	I-Error_Name
.	O
</s>
<s>
It	O
will	O
need	O
only	O
to	O
be	O
erased	O
,	O
which	O
is	O
much	O
easier	O
and	O
faster	O
than	O
the	O
read	O
–	O
erase	O
–	O
modify	O
–	O
write	O
process	O
needed	O
for	O
randomly	O
written	O
data	O
going	O
through	O
garbage	B-General_Concept
collection	I-General_Concept
.	O
</s>
<s>
The	O
peak	O
random	O
write	O
performance	O
on	O
an	O
SSD	B-Device
is	O
driven	O
by	O
plenty	O
of	O
free	O
blocks	O
after	O
the	O
SSD	B-Device
is	O
completely	O
garbage	B-General_Concept
collected	I-General_Concept
,	O
secure	O
erased	O
,	O
100%	O
TRIMed	O
,	O
or	O
newly	O
installed	O
.	O
</s>
<s>
The	O
maximum	O
speed	O
will	O
depend	O
upon	O
the	O
number	O
of	O
parallel	O
flash	O
channels	O
connected	O
to	O
the	O
SSD	B-Device
controller	I-Device
,	O
the	O
efficiency	O
of	O
the	O
firmware	B-Application
,	O
and	O
the	O
speed	O
of	O
the	O
flash	B-Device
memory	I-Device
in	O
writing	O
to	O
a	O
page	O
.	O
</s>
<s>
During	O
this	O
phase	O
the	O
write	B-Error_Name
amplification	I-Error_Name
will	O
be	O
the	O
best	O
it	O
can	O
ever	O
be	O
for	O
random	O
writes	O
and	O
will	O
be	O
approaching	O
one	O
.	O
</s>
<s>
Once	O
the	O
blocks	O
are	O
all	O
written	O
once	O
,	O
garbage	B-General_Concept
collection	I-General_Concept
will	O
begin	O
and	O
the	O
performance	O
will	O
be	O
gated	O
by	O
the	O
speed	O
and	O
efficiency	O
of	O
that	O
process	O
.	O
</s>
<s>
Write	B-Error_Name
amplification	I-Error_Name
in	O
this	O
phase	O
will	O
increase	O
to	O
the	O
highest	O
levels	O
the	O
drive	O
will	O
experience	O
.	O
</s>
<s>
The	O
overall	O
performance	O
of	O
an	O
SSD	B-Device
is	O
dependent	O
upon	O
a	O
number	O
of	O
factors	O
,	O
including	O
write	B-Error_Name
amplification	I-Error_Name
.	O
</s>
<s>
Writing	O
to	O
a	O
flash	B-Device
memory	I-Device
device	O
takes	O
longer	O
than	O
reading	O
from	O
it	O
.	O
</s>
<s>
An	O
SSD	B-Device
generally	O
uses	O
multiple	O
flash	B-Device
memory	I-Device
components	O
connected	O
in	O
parallel	O
as	O
channels	O
to	O
increase	O
performance	O
.	O
</s>
<s>
If	O
the	O
SSD	B-Device
has	O
a	O
high	O
write	B-Error_Name
amplification	I-Error_Name
,	O
the	O
controller	O
will	O
be	O
required	O
to	O
write	O
that	O
many	O
more	O
times	O
to	O
the	O
flash	B-Device
memory	I-Device
.	O
</s>
<s>
An	O
SSD	B-Device
with	O
a	O
low	O
write	B-Error_Name
amplification	I-Error_Name
will	O
not	O
need	O
to	O
write	O
as	O
much	O
data	O
and	O
can	O
therefore	O
be	O
finished	O
writing	O
sooner	O
than	O
a	O
drive	O
with	O
a	O
high	O
write	B-Error_Name
amplification	I-Error_Name
.	O
</s>
<s>
In	O
September	O
2008	O
,	O
Intel	O
announced	O
the	O
X25-M	O
SATA	O
SSD	B-Device
with	O
a	O
reported	O
WA	O
as	O
low	O
as	O
1.1	O
.	O
</s>
<s>
In	O
April	O
2009	O
,	O
SandForce	O
announced	O
the	O
SF-1000	O
SSD	B-Device
Processor	O
family	O
with	O
a	O
reported	O
WA	O
of	O
0.5	O
which	O
appears	O
to	O
come	O
from	O
some	O
form	O
of	O
data	B-General_Concept
compression	I-General_Concept
.	O
</s>
<s>
Before	O
this	O
announcement	O
,	O
a	O
write	B-Error_Name
amplification	I-Error_Name
of	O
1.0	O
was	O
considered	O
the	O
lowest	O
that	O
could	O
be	O
attained	O
with	O
an	O
SSD	B-Device
.	O
</s>
