<s>
ext4	B-Application
(	O
fourth	B-Application
extended	I-Application
filesystem	I-Application
)	O
is	O
a	O
journaling	B-Application
file	I-Application
system	I-Application
for	O
Linux	B-Operating_System
,	O
developed	O
as	O
the	O
successor	O
to	O
ext3	B-Application
.	O
</s>
<s>
ext4	B-Application
was	O
initially	O
a	O
series	O
of	O
backward-compatible	B-General_Concept
extensions	O
to	O
ext3	B-Application
,	O
many	O
of	O
them	O
originally	O
developed	O
by	O
Cluster	B-Application
File	I-Application
Systems	I-Application
for	O
the	O
Lustre	B-Application
file	I-Application
system	I-Application
between	O
2003	O
and	O
2006	O
,	O
meant	O
to	O
extend	O
storage	O
limits	O
and	O
add	O
other	O
performance	O
improvements	O
.	O
</s>
<s>
However	O
,	O
other	O
Linux	B-Operating_System
kernel	I-Operating_System
developers	O
opposed	O
accepting	O
extensions	O
to	O
ext3	B-Application
for	O
stability	O
reasons	O
,	O
and	O
proposed	O
to	O
fork	B-Application
the	O
source	O
code	O
of	O
ext3	B-Application
,	O
rename	B-General_Concept
it	O
as	O
ext4	B-Application
,	O
and	O
perform	O
all	O
the	O
development	O
there	O
,	O
without	O
affecting	O
existing	O
ext3	B-Application
users	O
.	O
</s>
<s>
This	O
proposal	O
was	O
accepted	O
,	O
and	O
on	O
28	O
June	O
2006	O
,	O
Theodore	O
Ts'o	O
,	O
the	O
ext3	B-Application
maintainer	O
,	O
announced	O
the	O
new	O
plan	O
of	O
development	O
for	O
ext4	B-Application
.	O
</s>
<s>
A	O
preliminary	O
development	O
version	O
of	O
ext4	B-Application
was	O
included	O
in	O
version	O
2.6.19	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
.	O
</s>
<s>
On	O
11	O
October	O
2008	O
,	O
the	O
patches	O
that	O
mark	O
ext4	B-Application
as	O
stable	O
code	O
were	O
merged	O
in	O
the	O
Linux	O
2.6.28	O
source	O
code	O
repositories	O
,	O
denoting	O
the	O
end	O
of	O
the	O
development	O
phase	O
and	O
recommending	O
ext4	B-Application
adoption	O
.	O
</s>
<s>
Kernel	B-Operating_System
2.6.28	O
,	O
containing	O
the	O
ext4	B-Application
filesystem	I-Application
,	O
was	O
finally	O
released	O
on	O
25	O
December	O
2008	O
.	O
</s>
<s>
On	O
15	O
January	O
2010	O
,	O
Google	B-Application
announced	O
that	O
it	O
would	O
upgrade	O
its	O
storage	O
infrastructure	O
from	O
ext2	B-Application
to	O
ext4	B-Application
.	O
</s>
<s>
On	O
14	O
December	O
2010	O
,	O
Google	B-Application
also	O
announced	O
it	O
would	O
use	O
ext4	B-Application
,	O
instead	O
of	O
YAFFS	B-Application
,	O
on	O
Android	B-Application
2.3	I-Application
.	O
</s>
<s>
ext4	B-Application
is	O
the	O
default	O
file	O
system	O
for	O
many	O
Linux	B-Operating_System
distributions	O
including	O
Debian	O
and	O
Ubuntu	B-Operating_System
.	O
</s>
<s>
The	O
ext4	B-Application
filesystem	I-Application
can	O
support	O
volumes	O
with	O
sizes	O
in	O
theory	O
up	O
to	O
64	O
zebibyte	O
(	O
ZiB	O
)	O
and	O
single	O
files	O
with	O
sizes	O
up	O
to	O
16	O
tebibytes	O
(	O
TiB	O
)	O
with	O
the	O
standard	O
4	B-Application
KiB	O
block	B-General_Concept
size	I-General_Concept
,	O
and	O
volumes	O
with	O
sizes	O
up	O
to	O
1	O
yobibyte	O
(	O
YiB	O
)	O
with	O
64	O
KiB	O
clusters	O
,	O
though	O
a	O
limitation	O
in	O
the	O
extent	O
format	O
makes	O
1	O
exbibyte	O
(	O
EiB	O
)	O
the	O
practical	O
limit	O
.	O
</s>
<s>
The	O
maximum	O
file	O
,	O
directory	O
,	O
and	O
filesystem	O
size	O
limits	O
grow	O
at	O
least	O
proportionately	O
with	O
the	O
filesystem	O
block	B-General_Concept
size	I-General_Concept
up	O
to	O
the	O
maximum	O
64	O
KiB	O
block	B-General_Concept
size	I-General_Concept
available	O
on	O
ARM	B-Architecture
and	O
PowerPC/Power	O
ISA	O
CPUs	O
.	O
</s>
<s>
Extents	B-Application
replace	O
the	O
traditional	O
block	B-General_Concept
mapping	I-General_Concept
scheme	O
used	O
by	O
ext2	B-Application
and	O
ext3	B-Application
.	O
</s>
<s>
An	O
extent	O
is	O
a	O
range	O
of	O
contiguous	O
physical	O
blocks	O
,	O
improving	O
large-file	O
performance	O
and	O
reducing	O
fragmentation	B-Architecture
.	O
</s>
<s>
A	O
single	O
extent	O
in	O
ext4	B-Application
can	O
map	O
up	O
to	O
128MiB	O
of	O
contiguous	O
space	O
with	O
a	O
4KiB	O
block	B-General_Concept
size	I-General_Concept
.	O
</s>
<s>
There	O
can	O
be	O
four	O
extents	B-Application
stored	O
directly	O
in	O
the	O
inode	B-Application
.	O
</s>
<s>
When	O
there	O
are	O
more	O
than	O
four	O
extents	B-Application
to	O
a	O
file	O
,	O
the	O
rest	O
of	O
the	O
extents	B-Application
are	O
indexed	O
in	O
a	O
tree	B-Application
.	O
</s>
<s>
ext4	B-Application
is	O
backward-compatible	B-General_Concept
with	O
ext3	B-Application
and	O
ext2	B-Application
,	O
making	O
it	O
possible	O
to	O
mount	B-Application
ext3	B-Application
and	O
ext2	B-Application
as	O
ext4	B-Application
.	O
</s>
<s>
This	O
will	O
slightly	O
improve	O
performance	O
,	O
because	O
certain	O
new	O
features	O
of	O
the	O
ext4	B-Application
implementation	O
can	O
also	O
be	O
used	O
with	O
ext3	B-Application
and	O
ext2	B-Application
,	O
such	O
as	O
the	O
new	O
block	O
allocation	O
algorithm	O
,	O
without	O
affecting	O
the	O
on-disk	O
format	O
.	O
</s>
<s>
ext3	B-Application
is	O
partially	O
forward-compatible	B-General_Concept
with	O
ext4	B-Application
.	O
</s>
<s>
Practically	O
,	O
ext4	B-Application
will	O
not	O
mount	B-Application
as	O
an	O
ext3	B-Application
filesystem	I-Application
out	O
of	O
the	O
box	O
,	O
unless	O
certain	O
new	O
features	O
are	O
disabled	O
when	O
creating	O
it	O
,	O
such	O
as	O
^extent	O
,	O
^flex_bg	O
,	O
^huge_file	O
,	O
^uninit_bg	O
,	O
^dir_nlink	O
,	O
and	O
^extra_isize	O
.	O
</s>
<s>
ext4	B-Application
can	O
pre-allocate	O
on-disk	O
space	O
for	O
a	O
file	O
.	O
</s>
<s>
In	O
ext4	B-Application
(	O
and	O
some	O
other	O
file	O
systems	O
such	O
as	O
XFS	B-Application
)	O
fallocate( )	O
,	O
a	O
new	O
system	B-Operating_System
call	I-Operating_System
in	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
,	O
can	O
be	O
used	O
.	O
</s>
<s>
ext4	B-Application
uses	O
a	O
performance	O
technique	O
called	O
allocate-on-flush	B-Application
,	O
also	O
known	O
as	O
delayed	B-Application
allocation	I-Application
.	O
</s>
<s>
That	O
is	O
,	O
ext4	B-Application
delays	O
block	O
allocation	O
until	O
data	O
is	O
flushed	O
to	O
disk	O
;	O
in	O
contrast	O
,	O
some	O
file	O
systems	O
allocate	O
blocks	O
immediately	O
,	O
even	O
when	O
the	O
data	O
goes	O
into	O
a	O
write	B-Language
cache	O
.	O
</s>
<s>
Delayed	B-Application
allocation	I-Application
improves	O
performance	O
and	O
reduces	O
fragmentation	B-Architecture
by	O
effectively	O
allocating	O
larger	O
amounts	O
of	O
data	O
at	O
a	O
time	O
.	O
</s>
<s>
ext4	B-Application
does	O
not	O
limit	O
the	O
number	O
of	O
subdirectories	O
in	O
a	O
single	O
directory	O
,	O
except	O
by	O
the	O
inherent	O
size	O
limit	O
of	O
the	O
directory	O
itself	O
.	O
</s>
<s>
(	O
In	O
ext3	B-Application
a	O
directory	O
can	O
have	O
at	O
most	O
32,000	O
subdirectories	O
.	O
)	O
</s>
<s>
To	O
allow	O
for	O
larger	O
directories	O
and	O
continued	O
performance	O
,	O
ext4	B-Application
in	O
Linux	O
2.6.23	O
and	O
later	O
turns	O
on	O
HTree	B-Library
indices	B-Data_Structure
(	O
a	O
specialized	O
version	O
of	O
a	O
B-tree	B-Architecture
)	O
by	O
default	O
,	O
which	O
allows	O
directories	O
up	O
to	O
approximately	O
10	O
–	O
12	O
million	O
entries	O
to	O
be	O
stored	O
in	O
the	O
2-level	O
HTree	B-Library
index	O
and	O
2GB	O
directory	O
size	O
limit	O
for	O
4KiB	O
block	B-General_Concept
size	I-General_Concept
,	O
depending	O
on	O
the	O
filename	O
length	O
.	O
</s>
<s>
In	O
Linux	B-Operating_System
4.12	O
and	O
later	O
the	O
largedir	O
feature	O
enabled	O
a	O
3-level	O
HTree	B-Library
and	O
directory	O
sizes	O
over	O
2GB	O
,	O
allowing	O
approximately	O
6	O
billion	O
entries	O
in	O
a	O
single	O
directory	O
.	O
</s>
<s>
ext4	B-Application
uses	O
checksums	B-Algorithm
in	O
the	O
journal	O
to	O
improve	O
reliability	O
,	O
since	O
the	O
journal	O
is	O
one	O
of	O
the	O
most	O
used	O
files	O
of	O
the	O
disk	O
.	O
</s>
<s>
This	O
feature	O
has	O
a	O
side	O
benefit	O
:	O
it	O
can	O
safely	O
avoid	O
a	O
disk	O
I/O	O
wait	O
during	O
journaling	B-Application
,	O
improving	O
performance	O
slightly	O
.	O
</s>
<s>
Journal	O
checksumming	O
was	O
inspired	O
by	O
a	O
research	O
article	O
from	O
the	O
University	O
of	O
Wisconsin	O
,	O
titled	O
IRON	O
File	O
Systems	O
(	O
specifically	O
,	O
section	O
6	O
,	O
called	O
"	O
transaction	O
checksums	B-Algorithm
"	O
)	O
,	O
with	O
modifications	O
within	O
the	O
implementation	O
of	O
compound	O
transactions	O
performed	O
by	O
the	O
IRON	O
file	O
system	O
(	O
originally	O
proposed	O
by	O
Sam	O
Naghshineh	O
in	O
the	O
RedHat	O
summit	O
)	O
.	O
</s>
<s>
In	O
ext4	B-Application
unallocated	O
block	O
groups	O
and	O
sections	O
of	O
the	O
inode	B-Application
table	O
are	O
marked	O
as	O
such	O
.	O
</s>
<s>
This	O
enables	O
e2fsck	B-Device
to	O
skip	O
them	O
entirely	O
and	O
greatly	O
reduces	O
the	O
time	O
it	O
takes	O
to	O
check	O
the	O
file	O
system	O
.	O
</s>
<s>
When	O
ext3	B-Application
appends	O
to	O
a	O
file	O
,	O
it	O
calls	O
the	O
block	O
allocator	O
,	O
once	O
for	O
each	O
block	O
.	O
</s>
<s>
Consequently	O
,	O
if	O
there	O
are	O
multiple	O
concurrent	O
writers	O
,	O
files	O
can	O
easily	O
become	O
fragmented	B-Application
on	O
disk	O
.	O
</s>
<s>
However	O
,	O
ext4	B-Application
uses	O
delayed	B-Application
allocation	I-Application
,	O
which	O
allows	O
it	O
to	O
buffer	O
data	O
and	O
allocate	O
groups	O
of	O
blocks	O
.	O
</s>
<s>
Consequently	O
,	O
the	O
multiblock	O
allocator	O
can	O
make	O
better	O
choices	O
about	O
allocating	O
files	O
contiguously	B-Architecture
on	O
disk	O
.	O
</s>
<s>
As	O
computers	O
become	O
faster	O
in	O
general	O
,	O
and	O
as	O
Linux	B-Operating_System
becomes	O
used	O
more	O
for	O
mission-critical	O
applications	O
,	O
the	O
granularity	O
of	O
second-based	O
timestamps	O
becomes	O
insufficient	O
.	O
</s>
<s>
To	O
solve	O
this	O
,	O
ext4	B-Application
provides	O
timestamps	O
measured	O
in	O
nanoseconds	O
.	O
</s>
<s>
In	O
addition	O
,	O
2bits	O
of	O
the	O
expanded	O
timestamp	O
field	O
are	O
added	O
to	O
the	O
most	O
significant	O
bits	O
of	O
the	O
seconds	O
field	O
of	O
the	O
timestamps	O
to	O
defer	O
the	O
year	B-Application
2038	I-Application
problem	I-Application
for	O
an	O
additional	O
408	O
years	O
.	O
</s>
<s>
ext4	B-Application
also	O
adds	O
support	O
for	O
time-of-creation	O
timestamps	O
.	O
</s>
<s>
But	O
,	O
as	O
Theodore	O
Ts'o	O
points	O
out	O
,	O
while	O
it	O
is	O
easy	O
to	O
add	O
an	O
extra	O
creation-date	O
field	O
in	O
the	O
inode	B-Application
(	O
thus	O
technically	O
enabling	O
support	O
for	O
these	O
timestamps	O
in	O
ext4	B-Application
)	O
,	O
it	O
is	O
more	O
difficult	O
to	O
modify	O
or	O
add	O
the	O
necessary	O
system	B-Operating_System
calls	I-Operating_System
,	O
like	O
stat( )	O
(	O
which	O
would	O
probably	O
require	O
a	O
new	O
version	O
)	O
and	O
the	O
various	O
libraries	B-Library
that	O
depend	O
on	O
them	O
(	O
like	O
glibc	B-Language
)	O
.	O
</s>
<s>
Therefore	O
,	O
the	O
creation	O
date	O
stored	O
by	O
ext4	B-Application
is	O
currently	O
only	O
available	O
to	O
user	O
programs	O
on	O
Linux	B-Operating_System
via	O
the	O
statx( )	O
API	O
.	O
</s>
<s>
Support	O
for	O
project	O
quotas	B-Application
was	O
added	O
in	O
Linux	B-Operating_System
kernel	I-Operating_System
4.4	O
on	O
8	O
Jan	O
2016	O
.	O
</s>
<s>
This	O
feature	O
allows	O
assigning	O
disk	B-Application
quota	I-Application
limits	O
to	O
a	O
particular	O
project	O
ID	O
.	O
</s>
<s>
This	O
allows	O
assigning	O
quota	B-Application
limits	O
to	O
a	O
particular	O
subdirectory	O
tree	B-Application
independent	O
of	O
file	O
access	O
permissions	O
on	O
the	O
file	O
,	O
such	O
as	O
user	O
and	O
project	O
quotas	B-Application
that	O
are	O
dependent	O
on	O
the	O
UID	O
and	O
GID	O
.	O
</s>
<s>
While	O
this	O
is	O
similar	O
to	O
a	O
directory	O
quota	B-Application
,	O
the	O
main	O
difference	O
is	O
that	O
the	O
same	O
project	O
ID	O
can	O
be	O
assigned	O
to	O
multiple	O
top-level	O
directories	O
and	O
is	O
not	O
strictly	O
hierarchical	O
.	O
</s>
<s>
Support	O
for	O
transparent	O
encryption	O
was	O
added	O
in	O
Linux	B-Operating_System
kernel	I-Operating_System
4.1	O
on	O
June	O
2015	O
.	O
</s>
<s>
The	O
lazyinit	O
feature	O
allows	O
cleaning	O
of	O
inode	B-Application
tables	O
in	O
background	O
,	O
speeding	O
initialization	O
when	O
creating	O
a	O
new	O
ext4	B-Application
file	O
system	O
.	O
</s>
<s>
It	O
is	O
available	O
since	O
2010	O
in	O
Linux	B-Operating_System
kernel	I-Operating_System
version	O
2.6.37	O
.	O
</s>
<s>
ext4	B-Application
enables	O
write	B-Language
barriers	O
by	O
default	O
.	O
</s>
<s>
It	O
ensures	O
that	O
file	O
system	O
metadata	O
is	O
correctly	O
written	O
and	O
ordered	O
on	O
disk	O
,	O
even	O
when	O
write	B-Language
caches	O
lose	O
power	O
.	O
</s>
<s>
This	O
goes	O
with	O
a	O
performance	O
cost	O
especially	O
for	O
applications	O
that	O
use	O
fsync	B-Language
heavily	O
or	O
create	O
and	O
delete	O
many	O
small	O
files	O
.	O
</s>
<s>
For	O
disks	O
with	O
a	O
battery-backed	O
write	B-Language
cache	O
,	O
disabling	O
barriers	O
(	O
option	O
'	O
barrier=0	O
 '	O
)	O
may	O
safely	O
improve	O
performance	O
.	O
</s>
<s>
In	O
2008	O
,	O
the	O
principal	O
developer	O
of	O
the	O
ext3	B-Application
and	O
ext4	B-Application
file	O
systems	O
,	O
Theodore	O
Ts'o	O
,	O
stated	O
that	O
although	O
ext4	B-Application
has	O
improved	O
features	O
,	O
it	O
is	O
not	O
a	O
major	O
advance	O
,	O
it	O
uses	O
old	O
technology	O
,	O
and	O
is	O
a	O
stop-gap	O
.	O
</s>
<s>
Ts'o	O
believes	O
that	O
Btrfs	B-Operating_System
is	O
the	O
better	O
direction	O
because	O
"	O
it	O
offers	O
improvements	O
in	O
scalability	O
,	O
reliability	O
,	O
and	O
ease	O
of	O
management	O
"	O
.	O
</s>
<s>
Btrfs	B-Operating_System
also	O
has	O
"	O
a	O
number	O
of	O
the	O
same	O
design	O
ideas	O
that	O
reiser3/4	O
had	O
"	O
.	O
</s>
<s>
However	O
,	O
ext4	B-Application
has	O
continued	O
to	O
gain	O
new	O
features	O
such	O
as	O
file	O
encryption	O
and	O
metadata	O
checksums	B-Algorithm
.	O
</s>
<s>
The	O
ext4	B-Application
file	O
system	O
does	O
not	O
honor	O
the	O
"	O
secure	O
deletion	O
"	O
file	B-Application
attribute	I-Application
,	O
which	O
is	O
supposed	O
to	O
cause	O
overwriting	O
of	O
files	O
upon	O
deletion	O
.	O
</s>
<s>
Because	O
delayed	B-Application
allocation	I-Application
changes	O
the	O
behavior	O
that	O
programmers	O
have	O
been	O
relying	O
on	O
with	O
ext3	B-Application
,	O
the	O
feature	O
poses	O
some	O
additional	O
risk	O
of	O
data	O
loss	O
in	O
cases	O
where	O
the	O
system	O
crashes	O
or	O
loses	O
power	O
before	O
all	O
of	O
the	O
data	O
has	O
been	O
written	O
to	O
disk	O
.	O
</s>
<s>
Due	O
to	O
this	O
,	O
ext4	B-Application
in	O
kernel	B-Operating_System
versions	O
2.6.30	O
and	O
later	O
automatically	O
handles	O
these	O
cases	O
as	O
ext3	B-Application
does	O
.	O
</s>
<s>
The	O
typical	O
scenario	O
in	O
which	O
this	O
might	O
occur	O
is	O
a	O
program	O
replacing	O
the	O
contents	O
of	O
a	O
file	O
without	O
forcing	O
a	O
write	B-Language
to	O
the	O
disk	O
with	O
fsync	B-Language
.	O
</s>
<s>
fd	O
=	O
open("file" ,O_TRUNC)	O
;	O
write(fd, data )	O
;	O
close(fd )	O
;	O
</s>
<s>
In	O
this	O
case	O
,	O
an	O
existing	O
file	O
is	O
truncated	O
at	O
the	O
time	O
of	O
open	B-Language
(	O
due	O
to	O
O_TRUNC	O
flag	O
)	O
,	O
then	O
new	O
data	O
is	O
written	O
out	O
.	O
</s>
<s>
Since	O
the	O
write	B-Language
can	O
take	O
some	O
time	O
,	O
there	O
is	O
an	O
opportunity	O
of	O
losing	O
contents	O
even	O
with	O
ext3	B-Application
,	O
but	O
usually	O
very	O
small	O
.	O
</s>
<s>
However	O
,	O
because	O
ext4	B-Application
can	O
delay	O
writing	O
file	O
data	O
for	O
a	O
long	O
time	O
,	O
this	O
opportunity	O
is	O
much	O
greater	O
.	O
</s>
<s>
If	O
the	O
write	B-Language
does	O
not	O
succeed	O
(	O
which	O
may	O
be	O
due	O
to	O
error	O
conditions	O
in	O
the	O
writing	O
program	O
,	O
or	O
due	O
to	O
external	O
conditions	O
such	O
as	O
a	O
full	O
disk	O
)	O
,	O
then	O
both	O
the	O
original	O
version	O
and	O
the	O
new	O
version	O
of	O
the	O
file	O
will	O
be	O
lost	O
,	O
and	O
the	O
file	O
may	O
be	O
corrupted	O
because	O
only	O
a	O
part	O
of	O
it	O
has	O
been	O
written	O
.	O
</s>
<s>
If	O
other	O
processes	O
have	O
the	O
file	O
open	B-Language
and	O
do	O
not	O
expect	O
its	O
contents	O
to	O
change	O
,	O
those	O
processes	O
may	O
crash	O
.	O
</s>
<s>
fd	O
=	O
open( 	O
"	O
file.new	O
"	O
)	O
;	O
write(fd, data )	O
;	O
close(fd )	O
;	O
rename( 	O
"	O
file.new	O
"	O
,	O
"	O
file	O
"	O
)	O
;	O
</s>
<s>
Replacing	O
files	O
by	O
the	O
rename( )	O
call	O
is	O
guaranteed	O
to	O
be	O
atomic	O
by	O
POSIX	O
standards	O
–	O
i.e.	O
</s>
<s>
Because	O
the	O
ext3	B-Application
default	O
"	O
ordered	O
"	O
journaling	B-Application
mode	O
guarantees	O
file	O
data	O
is	O
written	O
out	O
on	O
disk	O
before	O
metadata	O
,	O
this	O
technique	O
guarantees	O
that	O
either	O
the	O
old	O
or	O
the	O
new	O
file	O
contents	O
will	O
persist	O
on	O
disk	O
.	O
</s>
<s>
ext4	B-Application
's	O
delayed	B-Application
allocation	I-Application
breaks	O
this	O
expectation	O
,	O
because	O
the	O
file	O
write	B-Language
can	O
be	O
delayed	O
for	O
a	O
long	O
time	O
,	O
and	O
the	O
rename	B-General_Concept
is	O
usually	O
carried	O
out	O
before	O
new	O
file	O
contents	O
reach	O
the	O
disk	O
.	O
</s>
<s>
Using	O
fsync( )	O
more	O
often	O
to	O
reduce	O
the	O
risk	O
for	O
ext4	B-Application
could	O
lead	O
to	O
performance	O
penalties	O
on	O
ext3	B-Application
filesystems	I-Application
mounted	O
with	O
the	O
data	O
=	O
ordered	O
flag	O
(	O
the	O
default	O
on	O
most	O
Linux	B-Operating_System
distributions	O
)	O
.	O
</s>
<s>
In	O
response	O
,	O
ext4	B-Application
in	O
Linux	B-Operating_System
kernels	I-Operating_System
2.6.30	O
and	O
newer	O
detect	O
the	O
occurrence	O
of	O
these	O
common	O
cases	O
and	O
force	O
the	O
files	O
to	O
be	O
allocated	O
immediately	O
.	O
</s>
<s>
For	O
a	O
small	O
cost	O
in	O
performance	O
,	O
this	O
provides	O
semantics	O
similar	O
to	O
ext3	B-Application
ordered	O
mode	O
and	O
increases	O
the	O
chance	O
that	O
either	O
version	O
of	O
the	O
file	O
will	O
survive	O
the	O
crash	O
.	O
</s>
<s>
This	O
new	O
behavior	O
is	O
enabled	O
by	O
default	O
,	O
but	O
can	O
be	O
disabled	O
with	O
the	O
"	O
noauto_da_alloc	O
"	O
mount	B-Application
option	O
.	O
</s>
<s>
The	O
new	O
patches	O
have	O
become	O
part	O
of	O
the	O
mainline	O
kernel	B-Operating_System
2.6.30	O
,	O
but	O
various	O
distributions	O
chose	O
to	O
backport	O
them	O
to	O
2.6.28	O
or	O
2.6.29	O
.	O
</s>
<s>
The	O
only	O
way	O
to	O
be	O
safe	O
is	O
to	O
write	B-Language
and	O
use	O
software	O
that	O
does	O
fsync( )	O
when	O
it	O
needs	O
to	O
.	O
</s>
<s>
Performance	O
problems	O
can	O
be	O
minimized	O
by	O
limiting	O
crucial	O
disk	O
writes	O
that	O
need	O
fsync( )	O
to	O
occur	O
less	O
frequently	O
.	O
</s>
<s>
Linux	B-Operating_System
kernel	I-Operating_System
Virtual	O
File	O
System	O
is	O
a	O
subsystem	O
or	O
layer	O
inside	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
.	O
</s>
<s>
All	O
system	B-Operating_System
calls	I-Operating_System
related	O
to	O
files	O
(	O
or	O
pseudo	O
files	O
)	O
are	O
directed	O
to	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
Virtual	O
File	O
System	O
for	O
initial	O
processing	O
.	O
</s>
<s>
These	O
calls	O
,	O
coming	O
from	O
user	O
processes	O
,	O
are	O
the	O
standard	O
POSIX	O
calls	O
,	O
such	O
as	O
open	B-Language
,	O
read	B-Language
,	O
write	B-Language
,	O
lseek	O
,	O
etc	O
.	O
</s>
<s>
Currently	O
,	O
ext4	B-Application
has	O
full	O
support	O
on	O
non-Linux	O
operating	O
systems	O
.	O
</s>
<s>
Windows	O
can	O
access	O
ext4	B-Application
since	O
Windows	O
10	O
Insider	O
Preview	O
Build	O
20211	O
.	O
</s>
<s>
It	O
is	O
possible	O
thanks	O
to	O
Windows	O
Subsystem	O
for	O
Linux	B-Operating_System
(	O
WSL	O
)	O
which	O
was	O
introduced	O
with	O
Windows	O
10	O
Anniversary	O
Update	O
(	O
version	O
1607	O
)	O
on	O
2	O
August	O
2016	O
.	O
</s>
<s>
Paragon	O
offers	O
its	O
commercial	O
product	O
Linux	B-Operating_System
File	O
Systems	O
for	O
Windows	O
which	O
allows	O
read/write	O
capabilities	O
for	O
ext2/3/4	O
on	O
Windows	O
7	O
SP1/8/8.1/10	O
and	O
Windows	O
Server	O
2008	O
R2	O
SP1/2012/2016	O
.	O
</s>
<s>
macOS	B-Operating_System
has	O
full	O
ext2/3/4	O
read	B-Language
–	O
write	B-Language
capability	O
through	O
the	O
extFS	O
for	O
Mac	O
by	O
Paragon	O
Software	O
,	O
which	O
is	O
a	O
commercial	O
product	O
.	O
</s>
<s>
Free	O
software	O
such	O
as	O
ext4fuse	O
has	O
read-only	O
support	O
with	O
limited	O
functionality	O
.	O
</s>
