<s>
ext3	B-Application
,	O
or	O
third	B-Application
extended	I-Application
filesystem	I-Application
,	O
is	O
a	O
journaled	B-Application
file	I-Application
system	I-Application
that	O
is	O
commonly	O
used	O
by	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
.	O
</s>
<s>
It	O
used	O
to	O
be	O
the	O
default	O
file	B-Application
system	I-Application
for	O
many	O
popular	O
Linux	B-Application
distributions	I-Application
.	O
</s>
<s>
Stephen	O
Tweedie	O
first	O
revealed	O
that	O
he	O
was	O
working	O
on	O
extending	O
ext2	B-Application
in	O
Journaling	B-Application
the	O
Linux	B-Operating_System
ext2fs	B-Application
Filesystem	B-Application
in	O
a	O
1998	O
paper	O
,	O
and	O
later	O
in	O
a	O
February	O
1999	O
kernel	B-Operating_System
mailing	O
list	O
posting	O
.	O
</s>
<s>
The	O
filesystem	B-Application
was	O
merged	O
with	O
the	O
mainline	O
Linux	B-Operating_System
kernel	I-Operating_System
in	O
November	O
2001	O
from	O
2.4.15	O
onward	O
.	O
</s>
<s>
Its	O
main	O
advantage	O
over	O
ext2	B-Application
is	O
journaling	B-Application
,	O
which	O
improves	O
reliability	O
and	O
eliminates	O
the	O
need	O
to	O
check	O
the	O
file	B-Application
system	I-Application
after	O
an	O
unclean	O
shutdown	O
.	O
</s>
<s>
Its	O
successor	O
is	O
ext4	B-Application
.	O
</s>
<s>
The	O
performance	O
(	O
speed	O
)	O
of	O
ext3	B-Application
is	O
less	O
attractive	O
than	O
competing	O
Linux	B-Operating_System
filesystems	B-Application
,	O
such	O
as	O
ext4	B-Application
,	O
JFS	B-Application
,	O
ReiserFS	B-Application
,	O
and	O
XFS	B-Application
,	O
but	O
ext3	B-Application
has	O
a	O
significant	O
advantage	O
in	O
that	O
it	O
allows	O
in-place	O
upgrades	O
from	O
ext2	B-Application
without	O
having	O
to	O
back	B-Protocol
up	I-Protocol
and	O
restore	O
data	O
.	O
</s>
<s>
Benchmarks	O
suggest	O
that	O
ext3	B-Application
also	O
uses	O
less	O
CPU	O
power	O
than	O
ReiserFS	B-Application
and	O
XFS	B-Application
.	O
</s>
<s>
It	O
is	O
also	O
considered	O
safer	O
than	O
the	O
other	O
Linux	B-Operating_System
file	B-Application
systems	I-Application
,	O
due	O
to	O
its	O
relative	O
simplicity	O
and	O
wider	O
testing	O
base	O
.	O
</s>
<s>
ext3	B-Application
adds	O
the	O
following	O
features	O
to	O
ext2	B-Application
:	O
</s>
<s>
Without	O
these	O
features	O
,	O
any	O
ext3	B-Application
file	B-Application
system	I-Application
is	O
also	O
a	O
valid	O
ext2	B-Application
file	B-Application
system	I-Application
.	O
</s>
<s>
This	O
situation	O
has	O
allowed	O
well-tested	O
and	O
mature	O
file	B-Application
system	I-Application
maintenance	O
utilities	O
for	O
maintaining	O
and	O
repairing	O
ext2	B-Application
file	B-Application
systems	I-Application
to	O
also	O
be	O
used	O
with	O
ext3	B-Application
without	O
major	O
changes	O
.	O
</s>
<s>
The	O
ext2	B-Application
and	O
ext3	B-Application
file	B-Application
systems	I-Application
share	O
the	O
same	O
standard	O
set	O
of	O
utilities	O
,	O
e2fsprogs	B-Application
,	O
which	O
includes	O
an	O
fsck	B-Device
tool	O
.	O
</s>
<s>
The	O
close	O
relationship	O
also	O
makes	O
conversion	O
between	O
the	O
two	O
file	B-Application
systems	I-Application
(	O
both	O
forward	O
to	O
ext3	B-Application
and	O
backward	O
to	O
ext2	B-Application
)	O
straightforward	O
.	O
</s>
<s>
ext3	B-Application
lacks	O
"	O
modern	O
"	O
filesystem	B-Application
features	O
,	O
such	O
as	O
dynamic	O
inode	B-Application
allocation	O
and	O
extents	B-Application
.	O
</s>
<s>
The	O
file	B-Application
system	I-Application
metadata	O
is	O
all	O
in	O
fixed	O
,	O
well-known	O
locations	O
,	O
and	O
data	O
structures	O
have	O
some	O
redundancy	O
.	O
</s>
<s>
In	O
significant	O
data	O
corruption	O
,	O
ext2	B-Application
or	O
ext3	B-Application
may	O
be	O
recoverable	O
,	O
while	O
a	O
tree-based	O
file	B-Application
system	I-Application
may	O
not	O
.	O
</s>
<s>
The	O
maximum	O
number	O
of	O
blocks	B-General_Concept
for	O
ext3	B-Application
is	O
232	O
.	O
</s>
<s>
The	O
size	O
of	O
a	O
block	O
can	O
vary	O
,	O
affecting	O
the	O
maximum	O
number	O
of	O
files	O
and	O
the	O
maximum	O
size	O
of	O
the	O
file	B-Application
system	I-Application
:	O
</s>
<s>
Block	B-General_Concept
size	I-General_Concept
Maximumfile	O
size	O
Maximumfile-system	O
size	O
1	O
KiB	O
16	O
GiB	O
2	O
TiB	O
2	O
KiB	O
256	O
GiB	O
8	O
TiB	O
4	B-Application
KiB	O
2	O
TiB	O
16	O
TiB	O
8	O
KiBIn	O
Linux	B-Operating_System
,	O
8	O
KiB	O
block	B-General_Concept
size	I-General_Concept
is	O
only	O
available	O
on	O
architectures	O
which	O
allow	O
8	O
KiB	O
pages	B-Architecture
,	O
such	O
as	O
Alpha	B-Device
.	O
</s>
<s>
There	O
are	O
three	O
levels	O
of	O
journaling	B-Application
available	O
in	O
the	O
Linux	B-Operating_System
implementation	O
of	O
ext3	B-Application
:	O
</s>
<s>
Journal	B-Application
(	O
lowest	O
risk	O
)	O
Both	O
metadata	O
and	O
file	O
contents	O
are	O
written	O
to	O
the	O
journal	B-Application
before	O
being	O
committed	O
to	O
the	O
main	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Because	O
the	O
journal	B-Application
is	O
relatively	O
continuous	O
on	O
disk	O
,	O
this	O
can	O
improve	O
performance	O
,	O
if	O
the	O
journal	B-Application
has	O
enough	O
space	O
.	O
</s>
<s>
In	O
other	O
cases	O
,	O
performance	O
gets	O
worse	O
,	O
because	O
the	O
data	O
must	O
be	O
written	O
twice	O
—	O
once	O
to	O
the	O
journal	B-Application
,	O
and	O
once	O
to	O
the	O
main	O
part	O
of	O
the	O
filesystem	B-Application
.	O
</s>
<s>
Ordered	O
(	O
medium	O
risk	O
)	O
Only	O
metadata	O
is	O
journaled	O
;	O
file	O
contents	O
are	O
not	O
,	O
but	O
it	O
's	O
guaranteed	O
that	O
file	O
contents	O
are	O
written	O
to	O
disk	O
before	O
associated	O
metadata	O
is	O
marked	O
as	O
committed	O
in	O
the	O
journal	B-Application
.	O
</s>
<s>
This	O
is	O
the	O
default	O
on	O
many	O
Linux	B-Application
distributions	I-Application
.	O
</s>
<s>
If	O
there	O
is	O
a	O
power	O
outage	O
or	O
kernel	B-Operating_System
panic	I-Operating_System
while	O
a	O
file	O
is	O
being	O
written	O
or	O
appended	O
to	O
,	O
the	O
journal	B-Application
will	O
indicate	O
that	O
the	O
new	O
file	O
or	O
appended	O
data	O
has	O
not	O
been	O
"	O
committed	O
"	O
,	O
so	O
it	O
will	O
be	O
purged	O
by	O
the	O
cleanup	O
process	O
.	O
</s>
<s>
The	O
contents	O
might	O
be	O
written	O
before	O
or	O
after	O
the	O
journal	B-Application
is	O
updated	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
file	O
being	O
appended	O
to	O
may	O
be	O
marked	O
in	O
the	O
journal	B-Application
as	O
being	O
larger	O
than	O
it	O
actually	O
is	O
,	O
causing	O
garbage	O
at	O
the	O
end	O
.	O
</s>
<s>
Older	O
versions	O
of	O
files	O
could	O
also	O
appear	O
unexpectedly	O
after	O
a	O
journal	B-Application
recovery	O
.	O
</s>
<s>
The	O
lack	O
of	O
synchronization	O
between	O
data	O
and	O
journal	B-Application
is	O
faster	O
in	O
many	O
cases	O
.	O
</s>
<s>
JFS	B-Application
uses	O
this	O
level	O
of	O
journaling	B-Application
,	O
but	O
ensures	O
that	O
any	O
"	O
garbage	O
"	O
due	O
to	O
unwritten	O
data	O
is	O
zeroed	O
out	O
on	O
reboot	O
.	O
</s>
<s>
XFS	B-Application
also	O
uses	O
this	O
form	O
of	O
journaling	B-Application
.	O
</s>
<s>
In	O
all	O
three	O
modes	O
,	O
the	O
internal	O
structure	O
of	O
file	B-Application
system	I-Application
is	O
assured	O
to	O
be	O
consistent	O
even	O
after	O
a	O
crash	O
.	O
</s>
<s>
Because	O
ext3	B-Application
aims	O
to	O
be	O
backward-compatible	B-General_Concept
with	O
the	O
earlier	O
ext2	B-Application
,	O
many	O
of	O
the	O
on-disk	O
structures	O
are	O
similar	O
to	O
those	O
of	O
ext2	B-Application
.	O
</s>
<s>
Consequently	O
,	O
ext3	B-Application
lacks	O
recent	O
features	O
,	O
such	O
as	O
extents	B-Application
,	O
dynamic	O
allocation	O
of	O
inodes	B-Application
,	O
and	O
block	O
sub-allocation	O
.	O
</s>
<s>
A	O
directory	O
can	O
have	O
at	O
most	O
31998	O
subdirectories	O
,	O
because	O
an	O
inode	B-Application
can	O
have	O
at	O
most	O
32,000	O
links	O
(	O
each	O
direct	O
subdirectory	O
increases	O
their	O
parent	O
folder	O
inode	B-Application
link	O
counter	O
in	O
the	O
"	O
..	O
"	O
reference	O
)	O
.	O
</s>
<s>
On	O
ext3	B-Application
,	O
like	O
for	O
most	O
current	O
Linux	B-Operating_System
filesystems	B-Application
,	O
the	O
system	O
tool	O
"	O
fsck	B-Device
"	O
should	O
not	O
be	O
used	O
while	O
the	O
filesystem	B-Application
is	O
mounted	O
for	O
writing	O
.	O
</s>
<s>
Attempting	O
to	O
check	O
a	O
filesystem	B-Application
that	O
is	O
already	O
mounted	O
in	O
read/write	O
mode	O
will	O
(	O
very	O
likely	O
)	O
detect	O
inconsistencies	O
in	O
the	O
filesystem	B-Application
metadata	O
.	O
</s>
<s>
Where	O
filesystem	B-Application
metadata	O
is	O
changing	O
,	O
and	O
fsck	B-Device
applies	O
changes	O
in	O
an	O
attempt	O
to	O
bring	O
the	O
"	O
inconsistent	O
"	O
metadata	O
into	O
a	O
"	O
consistent	O
"	O
state	O
,	O
the	O
attempt	O
to	O
"	O
fix	O
"	O
the	O
inconsistencies	O
will	O
corrupt	O
the	O
filesystem	B-Application
.	O
</s>
<s>
There	O
is	O
no	O
online	O
ext3	B-Application
defragmentation	B-Application
tool	O
that	O
works	O
on	O
the	O
filesystem	B-Application
level	O
.	O
</s>
<s>
There	O
is	O
an	O
offline	O
ext2	B-Application
defragmenter	B-Application
,	O
e2defrag	O
.	O
</s>
<s>
However	O
,	O
e2defrag	O
may	O
destroy	O
data	O
,	O
depending	O
on	O
the	O
feature	O
bits	O
turned	O
on	O
in	O
the	O
filesystem	B-Application
;	O
it	O
does	O
not	O
know	O
how	O
to	O
handle	O
many	O
of	O
the	O
newer	O
ext3	B-Application
features	O
.	O
</s>
<s>
There	O
are	O
userspace	O
defragmentation	B-Application
tools	O
,	O
like	O
Shake	O
and	O
defrag	B-Application
.	O
</s>
<s>
Defrag	B-Application
works	O
by	O
copying	O
each	O
file	O
over	O
itself	O
.	O
</s>
<s>
However	O
,	O
this	O
strategy	O
works	O
only	O
if	O
the	O
file	B-Application
system	I-Application
has	O
enough	O
free	O
space	O
.	O
</s>
<s>
A	O
true	O
defragmentation	B-Application
tool	O
does	O
not	O
exist	O
for	O
ext3	B-Application
.	O
</s>
<s>
However	O
,	O
as	O
the	O
Linux	B-Operating_System
System	O
Administrator	O
Guide	O
states	O
,	O
"	O
Modern	O
Linux	B-Operating_System
filesystem(s )	O
keep	O
fragmentation	O
at	O
a	O
minimum	O
by	O
keeping	O
all	O
blocks	B-General_Concept
in	O
a	O
file	O
close	O
together	O
,	O
even	O
if	O
they	O
ca	O
n't	O
be	O
stored	O
in	O
consecutive	O
sectors	O
.	O
</s>
<s>
Some	O
filesystems	B-Application
,	O
like	O
ext3	B-Application
,	O
effectively	O
allocate	O
the	O
free	O
block	O
that	O
is	O
nearest	O
to	O
other	O
blocks	B-General_Concept
in	O
a	O
file	O
.	O
</s>
<s>
Therefore	O
it	O
is	O
not	O
necessary	O
to	O
worry	O
about	O
fragmentation	O
in	O
a	O
Linux	B-Operating_System
system.	O
"	O
</s>
<s>
While	O
ext3	B-Application
is	O
resistant	O
to	O
file	O
fragmentation	O
,	O
ext3	B-Application
can	O
get	O
fragmented	O
over	O
time	O
or	O
for	O
specific	O
usage	O
patterns	O
,	O
like	O
slowly	O
writing	O
large	O
files	O
.	O
</s>
<s>
Consequently	O
,	O
ext4	B-Application
(	O
the	O
successor	O
to	O
ext3	B-Application
)	O
has	O
an	O
online	O
filesystem	B-Application
defragmentation	B-Application
utility	O
e4defrag	O
and	O
currently	O
supports	O
extents	B-Application
(	O
contiguous	O
file	O
regions	O
)	O
.	O
</s>
<s>
ext3	B-Application
does	O
not	O
support	O
the	O
recovery	O
of	O
deleted	O
files	O
.	O
</s>
<s>
The	O
ext3	B-Application
driver	O
actively	O
deletes	O
files	O
by	O
wiping	O
file	O
inodes	B-Application
for	O
crash	O
safety	O
reasons	O
.	O
</s>
<s>
There	O
are	O
still	O
several	O
techniques	O
and	O
some	O
free	O
and	O
proprietary	O
software	O
for	O
recovery	O
of	O
deleted	O
or	O
lost	O
files	O
using	O
file	B-Application
system	I-Application
journal	B-Application
analysis	O
;	O
however	O
,	O
they	O
do	O
not	O
guarantee	O
any	O
specific	O
file	O
recovery	O
.	O
</s>
<s>
e3compr	O
is	O
an	O
unofficial	O
patch	O
for	O
ext3	B-Application
that	O
does	O
transparent	O
compression	B-General_Concept
.	O
</s>
<s>
It	O
compiles	O
and	O
boots	O
well	O
with	O
upstream	O
kernels	B-Operating_System
,	O
but	O
journaling	B-Application
is	O
not	O
implemented	O
yet	O
.	O
</s>
<s>
Unlike	O
a	O
number	O
of	O
modern	O
file	B-Application
systems	I-Application
,	O
ext3	B-Application
does	O
not	O
have	O
native	O
support	O
for	O
snapshots	B-Application
,	O
the	O
ability	O
to	O
quickly	O
capture	O
the	O
state	O
of	O
the	O
filesystem	B-Application
at	O
arbitrary	O
times	O
.	O
</s>
<s>
Instead	O
,	O
it	O
relies	O
on	O
less-space-efficient	O
,	O
volume-level	O
snapshots	B-Application
provided	O
by	O
the	O
Linux	B-Operating_System
LVM	B-Application
.	O
</s>
<s>
The	O
Next3	B-Application
file	B-Application
system	I-Application
is	O
a	O
modified	O
version	O
of	O
ext3	B-Application
which	O
offers	O
snapshots	B-Application
support	O
,	O
yet	O
retains	O
compatibility	O
with	O
the	O
ext3	B-Application
on-disk	O
format	O
.	O
</s>
<s>
ext3	B-Application
does	O
not	O
do	O
checksumming	O
when	O
writing	O
to	O
the	O
journal	B-Application
.	O
</s>
<s>
On	O
a	O
storage	O
device	O
with	O
extra	O
cache	O
,	O
if	O
barrier	O
=	O
1	O
is	O
not	O
enabled	O
as	O
a	O
mount	O
option	O
(	O
in	O
/etc/fstab	B-Protocol
)	O
,	O
and	O
if	O
the	O
hardware	O
is	O
doing	O
out-of-order	O
write	O
caching	O
,	O
one	O
runs	O
the	O
risk	O
of	O
severe	O
filesystem	B-Application
corruption	O
during	O
a	O
crash	O
.	O
</s>
<s>
If	O
hard	O
disk	O
writes	O
are	O
done	O
out-of-order	O
(	O
due	O
to	O
modern	O
hard	O
disks	O
caching	O
writes	O
in	O
order	O
to	O
amortize	B-General_Concept
write	O
speeds	O
)	O
,	O
it	O
is	O
likely	O
that	O
one	O
will	O
write	O
a	O
commit	O
block	O
of	O
a	O
transaction	O
before	O
the	O
other	O
relevant	O
blocks	B-General_Concept
are	O
written	O
.	O
</s>
<s>
If	O
a	O
power	O
failure	O
or	O
unrecoverable	O
crash	O
should	O
occur	O
before	O
the	O
other	O
blocks	B-General_Concept
get	O
written	O
,	O
the	O
system	O
will	O
have	O
to	O
be	O
rebooted	O
.	O
</s>
<s>
Upon	O
reboot	O
,	O
the	O
file	B-Application
system	I-Application
will	O
replay	O
the	O
log	O
as	O
normal	O
,	O
and	O
replay	O
the	O
"	O
winners	O
"	O
(	O
transactions	O
with	O
a	O
commit	O
block	O
,	O
including	O
the	O
invalid	O
transaction	O
above	O
,	O
which	O
happened	O
to	O
be	O
tagged	O
with	O
a	O
valid	O
commit	O
block	O
)	O
.	O
</s>
<s>
The	O
unfinished	O
disk	O
write	O
above	O
will	O
thus	O
proceed	O
,	O
but	O
using	O
corrupt	O
journal	B-Application
data	O
.	O
</s>
<s>
The	O
file	B-Application
system	I-Application
will	O
thus	O
mistakenly	O
overwrite	O
normal	O
data	O
with	O
corrupt	O
data	O
while	O
replaying	O
the	O
journal	B-Application
.	O
</s>
<s>
If	O
checksums	B-Algorithm
had	O
been	O
used	O
,	O
where	O
the	O
blocks	B-General_Concept
of	O
the	O
"	O
fake	O
winner	O
"	O
transaction	O
were	O
tagged	O
with	O
a	O
mutual	O
checksum	B-Algorithm
,	O
the	O
file	B-Application
system	I-Application
could	O
have	O
known	O
better	O
and	O
not	O
replayed	O
the	O
corrupt	O
data	O
onto	O
the	O
disk	O
.	O
</s>
<s>
Journal	B-Application
checksumming	O
has	O
been	O
added	O
to	O
ext4	B-Application
.	O
</s>
<s>
Filesystems	B-Application
going	O
through	O
the	O
device	O
mapper	O
interface	O
(	O
including	O
software	O
RAID	B-Architecture
and	O
LVM	B-Application
implementations	O
)	O
may	O
not	O
support	O
barriers	O
,	O
and	O
will	O
issue	O
a	O
warning	O
if	O
that	O
mount	O
option	O
is	O
used	O
.	O
</s>
<s>
Applications	O
like	O
databases	O
expect	O
a	O
call	O
to	O
fsync( )	O
to	O
flush	O
pending	O
writes	O
to	O
disk	O
,	O
and	O
the	O
barrier	O
implementation	O
does	O
n't	O
always	O
clear	O
the	O
drive	O
's	O
write	O
cache	O
in	O
response	O
to	O
that	O
call	O
.	O
</s>
<s>
It	O
is	O
also	O
known	O
that	O
sometimes	O
some	O
virtualization	B-General_Concept
technologies	O
do	O
not	O
properly	O
forward	O
fsync	B-Language
or	O
flush	O
commands	O
to	O
the	O
underlying	O
devices	O
(	O
files	O
,	O
volumes	O
,	O
disk	O
)	O
from	O
a	O
guest	O
operating	O
system	O
.	O
</s>
<s>
There	O
are	O
so	O
many	O
ways	O
to	O
handle	O
fsync	B-Language
and	O
write	O
cache	O
handling	O
incorrectly	O
,	O
it	O
is	O
safer	O
to	O
assume	O
that	O
cache	O
flushing	O
does	O
not	O
work	O
unless	O
it	O
is	O
explicitly	O
tested	O
,	O
regardless	O
of	O
how	O
reliable	O
individual	O
components	O
are	O
believed	O
to	O
be	O
.	O
</s>
<s>
Ext3	B-Application
stores	O
dates	O
as	O
Unix	B-Operating_System
time	I-Operating_System
using	O
four	O
bytes	O
in	O
the	O
file	O
header	O
.	O
</s>
<s>
32	O
bits	O
does	O
not	O
give	O
enough	O
scope	O
to	O
continue	O
processing	O
files	O
beyond	O
January	O
18	O
,	O
2038	O
-	O
the	O
Year	B-Application
2038	I-Application
problem	I-Application
.	I-Application
</s>
<s>
On	O
June	O
28	O
,	O
2006	O
,	O
Theodore	O
Ts'o	O
,	O
the	O
principal	O
developer	O
of	O
ext3	B-Application
,	O
announced	O
an	O
enhanced	O
version	O
,	O
called	O
ext4	B-Application
.	O
</s>
<s>
On	O
October	O
11	O
,	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
marking	O
the	O
end	O
of	O
the	O
development	O
phase	O
and	O
recommending	O
its	O
adoption	O
.	O
</s>
<s>
In	O
2008	O
,	O
Ts'o	O
stated	O
that	O
although	O
ext4	B-Application
has	O
improved	O
features	O
such	O
as	O
being	O
much	O
faster	O
than	O
ext3	B-Application
,	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
Ts'o	O
believes	O
that	O
Btrfs	B-Operating_System
is	O
the	O
better	O
direction	O
,	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>
