<s>
Journaled	B-Application
File	I-Application
System	I-Application
(	O
JFS	B-Application
)	O
is	O
a	O
64-bit	B-Device
journaling	B-Application
file	I-Application
system	I-Application
created	O
by	O
IBM	O
.	O
</s>
<s>
There	O
are	O
versions	O
for	O
AIX	B-Application
,	O
OS/2	B-Application
,	O
eComStation	B-Device
,	O
ArcaOS	B-Device
and	O
Linux	B-Application
operating	I-Application
systems	I-Application
.	O
</s>
<s>
The	O
latter	O
is	O
available	O
as	O
free	O
software	O
under	O
the	O
terms	O
of	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
(	O
GPL	B-License
)	O
.	O
</s>
<s>
HP-UX	B-Application
has	O
another	O
,	O
different	O
filesystem	O
named	O
JFS	B-Application
that	O
is	O
actually	O
an	O
OEM	O
version	O
of	O
Veritas	O
Software	O
's	O
VxFS	B-Application
.	O
</s>
<s>
In	O
the	O
AIX	B-Application
operating	I-Application
system	I-Application
,	O
two	O
generations	O
of	O
JFS	B-Application
 '	O
exist	O
,	O
which	O
are	O
called	O
JFS	B-Application
(	O
JFS1	O
)	O
and	O
JFS2	B-Application
respectively	O
.	O
</s>
<s>
In	O
other	O
operating	B-General_Concept
systems	I-General_Concept
,	O
such	O
as	O
OS/2	B-Application
and	O
Linux	B-Operating_System
,	O
only	O
the	O
second	O
generation	O
exists	O
and	O
is	O
called	O
simply	O
JFS	B-Application
.	O
</s>
<s>
This	O
should	O
not	O
be	O
confused	O
with	O
JFS	B-Application
in	O
AIX	B-Application
that	O
actually	O
refers	O
to	O
JFS1	O
.	O
</s>
<s>
IBM	O
introduced	O
JFS	B-Application
with	O
the	O
initial	O
release	O
of	O
AIX	B-Application
version	O
3.1	O
in	O
February	O
1990	O
.	O
</s>
<s>
This	O
file	O
system	O
,	O
now	O
called	O
JFS1	O
on	O
AIX	B-Application
,	O
was	O
the	O
premier	O
file	O
system	O
for	O
AIX	B-Application
over	O
the	O
following	O
decade	O
and	O
was	O
installed	O
in	O
thousands	O
or	O
millions	O
of	O
customers	O
 '	O
AIX	B-Application
systems	O
.	O
</s>
<s>
Historically	O
,	O
the	O
JFS1	O
file	O
system	O
is	O
very	O
closely	O
tied	O
to	O
the	O
memory	O
manager	O
of	O
AIX	B-Application
,	O
which	O
is	O
a	O
typical	O
design	O
for	O
a	O
file	O
system	O
supporting	O
only	O
one	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Another	O
goal	O
was	O
to	O
have	O
a	O
more	O
portable	O
file	O
system	O
,	O
capable	O
of	O
running	O
on	O
multiple	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
After	O
several	O
years	O
of	O
designing	O
,	O
coding	O
,	O
and	O
testing	O
,	O
the	O
new	O
JFS	B-Application
was	O
first	O
shipped	O
in	O
OS/2	B-Application
Warp	B-Application
Server	I-Application
for	O
eBusiness	O
in	O
April	O
1999	O
,	O
and	O
then	O
in	O
OS/2	B-Application
Warp	O
Client	O
in	O
October	O
2000	O
.	O
</s>
<s>
In	O
December	O
1999	O
,	O
a	O
snapshot	O
of	O
the	O
original	O
OS/2	B-Application
JFS	B-Application
source	O
was	O
granted	O
to	O
the	O
open	B-License
source	I-License
community	O
and	O
work	O
was	O
begun	O
to	O
port	O
JFS	B-Application
to	O
Linux	B-Operating_System
.	O
</s>
<s>
The	O
first	O
stable	O
release	O
of	O
JFS	B-Application
for	O
Linux	B-Operating_System
appeared	O
in	O
June	O
2001	O
.	O
</s>
<s>
The	O
JFS	B-Application
for	O
Linux	B-Operating_System
project	O
is	O
maintained	O
by	O
a	O
small	O
group	O
of	O
contributors	O
known	O
as	O
the	O
JFS	B-Application
Core	O
Team	O
.	O
</s>
<s>
This	O
release	O
of	O
sources	O
also	O
worked	O
to	O
form	O
the	O
basis	O
of	O
a	O
re-port	O
back	O
to	O
OS/2	B-Application
of	O
the	O
open-source	B-License
JFS	B-Application
.	O
</s>
<s>
In	O
parallel	O
with	O
this	O
effort	O
,	O
some	O
of	O
the	O
JFS	B-Application
development	O
team	O
returned	O
to	O
the	O
AIX	B-Application
Operating	I-Application
System	I-Application
Development	O
Group	O
in	O
1997	O
and	O
started	O
to	O
move	O
this	O
new	O
JFS	B-Application
source	O
base	O
to	O
the	O
AIX	B-Application
operating	I-Application
system	I-Application
.	O
</s>
<s>
In	O
May	O
2001	O
,	O
a	O
second	O
journaled	B-Application
file	I-Application
system	I-Application
,	O
Enhanced	O
Journaled	B-Application
File	I-Application
System	I-Application
(	O
JFS2	B-Application
)	O
,	O
was	O
made	O
available	O
for	O
AIX	B-Application
5L	O
.	O
</s>
<s>
Early	O
in	O
2008	O
there	O
was	O
speculation	O
that	O
IBM	O
is	O
no	O
longer	O
interested	O
in	O
maintaining	O
JFS	B-Application
and	O
thus	O
it	O
should	O
not	O
be	O
used	O
in	O
production	O
environments	O
.	O
</s>
<s>
However	O
,	O
Dave	O
Kleikamp	O
,	O
a	O
member	O
of	O
the	O
IBM	O
Linux	B-Operating_System
Technology	O
Center	O
and	O
JFS	B-Application
Core	O
Team	O
,	O
explained	O
that	O
they	O
still	O
follow	O
changes	O
in	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
and	O
try	O
to	O
fix	O
potential	O
software	B-Error_Name
bugs	I-Error_Name
.	O
</s>
<s>
In	O
2012	O
,	O
TRIM	O
command	O
support	O
for	O
solid-state	B-Device
drives	I-Device
was	O
added	O
to	O
JFS	B-Application
.	O
</s>
<s>
JFS	B-Application
supports	O
the	O
following	O
features	O
.	O
</s>
<s>
JFS	B-Application
is	O
a	O
journaling	B-Application
file	I-Application
system	I-Application
.	O
</s>
<s>
Rather	O
than	O
adding	O
journaling	B-Application
as	O
an	O
add-on	O
feature	O
like	O
in	O
the	O
ext3	B-Application
file	O
system	O
,	O
it	O
was	O
implemented	O
from	O
the	O
start	O
.	O
</s>
<s>
JFS	B-Application
journals	O
metadata	O
only	O
,	O
which	O
means	O
that	O
metadata	O
will	O
remain	O
consistent	O
but	O
user	O
files	O
may	O
be	O
corrupted	O
after	O
a	O
crash	O
or	O
power	O
loss	O
.	O
</s>
<s>
JFS	B-Application
's	O
journaling	B-Application
is	O
similar	O
to	O
XFS	B-Application
in	O
that	O
it	O
only	O
journals	O
parts	O
of	O
the	O
inode	B-Application
.	O
</s>
<s>
JFS	B-Application
uses	O
a	O
B+	O
tree	O
to	O
accelerate	O
lookups	O
in	O
directories	O
.	O
</s>
<s>
JFS	B-Application
can	O
store	O
8	O
entries	O
of	O
a	O
directory	O
in	O
the	O
directory	O
's	O
inode	B-Application
before	O
moving	O
the	O
entries	O
to	O
a	O
B+	O
tree	O
.	O
</s>
<s>
JFS	B-Application
also	O
indexes	O
extents	B-Application
in	O
a	O
B+	O
tree	O
.	O
</s>
<s>
JFS	B-Application
dynamically	O
allocates	O
space	O
for	O
disk	O
inodes	B-Application
as	O
necessary	O
.	O
</s>
<s>
Each	O
inode	B-Application
is	O
512	O
bytes	O
.	O
</s>
<s>
32	O
inodes	B-Application
are	O
allocated	O
on	O
a	O
16	O
kB	O
Extent	B-Application
.	O
</s>
<s>
JFS	B-Application
allocates	O
files	O
as	O
an	O
extent	B-Application
.	O
</s>
<s>
An	O
extent	B-Application
is	O
a	O
variable-length	O
sequence	O
of	O
Aggregate	O
blocks	O
.	O
</s>
<s>
An	O
extent	B-Application
may	O
be	O
located	O
in	O
several	O
allocation	B-Application
groups	I-Application
.	O
</s>
<s>
To	O
solve	O
this	O
the	O
extents	B-Application
are	O
indexed	O
in	O
a	O
B+	O
tree	O
for	O
better	O
performance	O
when	O
locating	O
the	O
extent	B-Application
locations	O
.	O
</s>
<s>
Compression	B-General_Concept
is	O
supported	O
only	O
in	O
JFS1	O
on	O
AIX	B-Application
and	O
uses	O
a	O
variation	O
of	O
the	O
LZ	B-Algorithm
algorithm	I-Algorithm
.	O
</s>
<s>
Because	O
of	O
high	O
CPU	O
usage	O
and	O
increased	O
free	O
space	O
fragmentation	B-Application
,	O
compression	B-General_Concept
is	O
not	O
recommended	O
for	O
use	O
other	O
than	O
on	O
a	O
single	O
user	O
workstation	B-Device
or	O
off-line	O
backup	B-Protocol
areas	O
.	O
</s>
<s>
JFS	B-Application
normally	O
applies	O
read-shared	O
,	O
write-exclusive	O
locking	O
to	O
files	O
,	O
which	O
avoids	O
data	O
inconsistencies	O
but	O
imposes	O
write	O
serialization	O
at	O
the	O
file	O
level	O
.	O
</s>
<s>
JFS	B-Application
uses	O
allocation	B-Application
groups	I-Application
.	O
</s>
<s>
Allocation	B-Application
groups	I-Application
divide	O
the	O
aggregate	O
space	O
into	O
chunks	O
.	O
</s>
<s>
This	O
allows	O
JFS	B-Application
to	O
use	O
resource	O
allocation	O
policies	O
to	O
achieve	O
great	O
I/O	O
performance	O
.	O
</s>
<s>
The	O
first	O
policy	O
is	O
to	O
try	O
to	O
cluster	O
disk	O
blocks	O
and	O
disk	O
inodes	B-Application
for	O
related	O
data	O
in	O
the	O
same	O
AG	B-Application
in	O
order	O
to	O
achieve	O
good	O
locality	O
for	O
the	O
disk	O
.	O
</s>
<s>
The	O
second	O
policy	O
is	O
to	O
distribute	O
unrelated	O
data	O
throughout	O
the	O
file	O
system	O
in	O
an	O
attempt	O
to	O
minimize	O
free-space	O
fragmentation	B-Application
.	O
</s>
<s>
When	O
there	O
is	O
an	O
open	O
file	O
JFS	B-Application
will	O
lock	O
the	O
AG	B-Application
the	O
file	O
resides	O
in	O
and	O
only	O
allow	O
the	O
open	O
file	O
to	O
grow	O
.	O
</s>
<s>
This	O
reduces	O
fragmentation	B-Application
as	O
only	O
the	O
open	O
file	O
can	O
write	O
to	O
the	O
AG	B-Application
.	O
</s>
<s>
In	O
the	O
Linux	B-Application
operating	I-Application
system	I-Application
,	O
JFS	B-Application
is	O
supported	O
with	O
the	O
kernel	B-Operating_System
module	O
(	O
since	O
the	O
kernel	B-Operating_System
version	O
2.4.18pre9-ac4	O
)	O
and	O
the	O
complementary	O
userspace	B-Operating_System
utilities	O
packaged	O
under	O
the	O
name	O
JFSutils	O
.	O
</s>
<s>
Most	O
Linux	B-Application
distributions	I-Application
support	O
JFS	B-Application
unless	O
it	O
is	O
specifically	O
removed	O
due	O
to	O
space	O
restrictions	O
,	O
such	O
as	O
on	O
live	O
CDs	O
.	O
</s>
<s>
According	O
to	O
benchmarks	O
of	O
the	O
available	O
filesystems	O
for	O
Linux	B-Operating_System
,	O
JFS	B-Application
is	O
fast	O
and	O
reliable	O
,	O
with	O
consistently	O
good	O
performance	O
under	O
different	O
kinds	O
of	O
load	O
.	O
</s>
<s>
Actual	O
usage	O
of	O
JFS	B-Application
in	O
Linux	B-Operating_System
is	O
uncommon	O
,	O
as	O
ext4	B-Application
typically	O
offers	O
better	O
performance	O
.	O
</s>
<s>
JFS	B-Application
does	O
have	O
a	O
niche	O
role	O
in	O
Linux	B-Operating_System
:	O
it	O
offers	O
a	O
case-insensitive	O
mount	O
option	O
,	O
unlike	O
most	O
other	O
Linux	B-Operating_System
file	O
systems	O
.	O
</s>
<s>
There	O
are	O
also	O
potential	O
problems	O
with	O
JFS	B-Application
,	O
such	O
as	O
its	O
implementation	O
of	O
journal	O
writes	O
.	O
</s>
