<s>
XFS	B-Application
is	O
a	O
high-performance	O
64-bit	B-Device
journaling	B-Application
file	I-Application
system	I-Application
created	O
by	O
Silicon	O
Graphics	O
,	O
Inc	O
(	O
SGI	O
)	O
in	O
1993	O
.	O
</s>
<s>
It	O
was	O
the	O
default	O
file	O
system	O
in	O
SGI	O
's	O
IRIX	B-Operating_System
operating	O
system	O
starting	O
with	O
its	O
version	O
5.3	O
.	O
</s>
<s>
XFS	B-Application
was	O
ported	O
to	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
in	O
2001	O
;	O
as	O
of	O
June	O
2014	O
,	O
XFS	B-Application
is	O
supported	O
by	O
most	O
Linux	B-Application
distributions	I-Application
;	O
Red	O
Hat	O
Enterprise	O
Linux	B-Operating_System
uses	O
it	O
as	O
its	O
default	O
file	O
system	O
.	O
</s>
<s>
XFS	B-Application
excels	O
in	O
the	O
execution	O
of	O
parallel	O
input/output	B-General_Concept
(	O
I/O	B-General_Concept
)	O
operations	O
due	O
to	O
its	O
design	O
,	O
which	O
is	O
based	O
on	O
allocation	B-Application
groups	I-Application
(	O
a	O
type	O
of	O
subdivision	O
of	O
the	O
physical	O
volumes	O
in	O
which	O
XFS	B-Application
is	O
used	O
-	O
also	O
shortened	O
to	O
AGs	B-Application
)	O
.	O
</s>
<s>
Because	O
of	O
this	O
,	O
XFS	B-Application
enables	O
extreme	O
scalability	O
of	O
I/O	B-General_Concept
threads	O
,	O
file	O
system	O
bandwidth	O
,	O
and	O
size	O
of	O
files	B-Operating_System
and	O
of	O
the	O
file	O
system	O
itself	O
when	O
spanning	O
multiple	O
physical	O
storage	O
devices	O
.	O
</s>
<s>
XFS	B-Application
ensures	O
the	O
consistency	O
of	O
data	O
by	O
employing	O
metadata	O
journaling	B-Application
and	O
supporting	O
write	B-General_Concept
barriers	I-General_Concept
.	O
</s>
<s>
Space	O
allocation	O
is	O
performed	O
via	O
extents	B-Application
with	O
data	O
structures	O
stored	O
in	O
B+	O
trees	O
,	O
improving	O
the	O
overall	O
performance	O
of	O
the	O
file	O
system	O
,	O
especially	O
when	O
handling	O
large	O
files	B-Operating_System
.	O
</s>
<s>
Delayed	B-Application
allocation	I-Application
assists	O
in	O
the	O
prevention	O
of	O
file	B-Application
system	I-Application
fragmentation	I-Application
;	O
online	O
defragmentation	B-Application
is	O
also	O
supported	O
.	O
</s>
<s>
A	O
feature	O
unique	O
to	O
XFS	B-Application
is	O
the	O
pre-allocation	O
of	O
I/O	B-General_Concept
bandwidth	O
at	O
a	O
pre-determined	O
rate	O
;	O
this	O
is	O
suitable	O
for	O
many	O
real-time	O
applications	O
.	O
</s>
<s>
However	O
,	O
this	O
feature	O
was	O
supported	O
only	O
on	O
IRIX	B-Operating_System
,	O
and	O
only	O
with	O
specialized	O
hardware	O
.	O
</s>
<s>
Silicon	O
Graphics	O
began	O
development	O
of	O
XFS	B-Application
(	O
"	O
X	O
"	O
was	O
meant	O
to	O
be	O
filled	O
in	O
later	O
but	O
never	O
was	O
)	O
in	O
1993	O
.	O
</s>
<s>
The	O
file	O
system	O
was	O
released	O
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
(	O
GPL	B-License
)	O
in	O
May	O
1999	O
.	O
</s>
<s>
A	O
team	O
led	O
by	O
Steve	O
Lord	O
at	O
SGI	O
ported	O
it	O
to	O
Linux	B-Operating_System
,	O
and	O
first	O
support	O
by	O
a	O
Linux	B-Application
distribution	I-Application
came	O
in	O
2001	O
.	O
</s>
<s>
This	O
support	O
gradually	O
became	O
available	O
in	O
almost	O
all	O
Linux	B-Application
distributions	I-Application
.	O
</s>
<s>
Initial	O
support	O
for	O
XFS	B-Application
in	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
came	O
through	O
patches	O
from	O
SGI	O
.	O
</s>
<s>
It	O
merged	O
into	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
mainline	O
for	O
the	O
2.6	O
series	O
,	O
and	O
separately	O
merged	O
in	O
February	O
2004	O
into	O
the	O
2.4	O
series	O
in	O
version	O
2.4.25	O
,	O
making	O
XFS	B-Application
almost	O
universally	O
available	O
on	O
Linux	B-Operating_System
systems	O
.	O
</s>
<s>
Gentoo	B-Application
Linux	I-Application
became	O
the	O
first	O
Linux	B-Application
distribution	I-Application
to	O
introduce	O
an	O
option	O
for	O
XFS	B-Application
as	O
the	O
default	O
filesystem	O
in	O
mid-2002	O
.	O
</s>
<s>
FreeBSD	B-Operating_System
added	O
read-only	O
support	O
for	O
XFS	B-Application
in	O
December	O
2005	O
,	O
and	O
in	O
June	O
2006	O
introduced	O
experimental	O
write	O
support	O
.	O
</s>
<s>
However	O
,	O
this	O
was	O
intended	O
only	O
as	O
an	O
aid	O
in	O
migration	O
from	O
Linux	B-Operating_System
,	O
not	O
as	O
a	O
"	O
main	O
"	O
file	O
system	O
.	O
</s>
<s>
FreeBSD	B-Operating_System
10	O
removed	O
support	O
for	O
XFS	B-Application
.	O
</s>
<s>
In	O
2009	O
,	O
version	O
5.4	O
of	O
64-bit	B-Device
Red	O
Hat	O
Enterprise	O
Linux	B-Operating_System
(	O
RHEL	O
)	O
Linux	B-Application
distribution	I-Application
contained	O
the	O
necessary	O
kernel	B-Operating_System
support	O
for	O
the	O
creation	O
and	O
usage	O
of	O
XFS	B-Application
file	O
systems	O
,	O
but	O
lacked	O
the	O
corresponding	O
command-line	O
tools	O
.	O
</s>
<s>
RHEL6.0	O
,	O
released	O
in	O
2010	O
,	O
includes	O
XFS	B-Application
support	O
for	O
a	O
fee	O
as	O
part	O
of	O
Red	O
Hat	O
's	O
"	O
scalable	O
file	O
system	O
add-on	O
"	O
.	O
</s>
<s>
Oracle	O
Linux	B-Operating_System
6	O
,	O
released	O
in	O
2011	O
,	O
also	O
includes	O
an	O
option	O
for	O
using	O
XFS	B-Application
.	O
</s>
<s>
RHEL7.0	O
,	O
released	O
in	O
June	O
2014	O
,	O
uses	O
XFS	B-Application
as	O
its	O
default	O
file	O
system	O
,	O
including	O
support	O
for	O
using	O
XFS	B-Application
for	O
the	O
/boot	O
partition	B-Application
,	O
which	O
previously	O
was	O
not	O
practical	O
due	O
to	O
bugs	O
in	O
the	O
GRUB	B-Application
bootloader	O
.	O
</s>
<s>
Linux	B-Operating_System
kernel	I-Operating_System
4.8	O
in	O
August	O
2016	O
added	O
a	O
new	O
feature	O
,	O
"	O
reverse	O
mapping	O
"	O
.	O
</s>
<s>
This	O
is	O
the	O
foundation	O
for	O
a	O
large	O
set	O
of	O
planned	O
features	O
:	O
snapshots	B-Application
,	O
copy-on-write	B-Language
(	O
COW	O
)	O
data	O
,	O
data	B-General_Concept
deduplication	I-General_Concept
,	O
reflink	O
copies	O
,	O
online	O
data	O
and	O
metadata	O
scrubbing	B-Error_Name
,	O
highly	O
accurate	O
reporting	O
of	O
data	O
loss	O
or	O
bad	O
sectors	O
,	O
and	O
significantly	O
improved	O
reconstruction	O
of	O
damaged	O
or	O
corrupted	O
filesystems	O
.	O
</s>
<s>
This	O
work	O
required	O
changes	O
to	O
XFS	B-Application
's	O
on-disk	O
format	O
.	O
</s>
<s>
Linux	B-Operating_System
kernel	I-Operating_System
5.10	O
,	O
released	O
in	O
December	O
2020	O
,	O
introduced	O
"	O
bigtime	O
"	O
,	O
to	O
store	O
inode	B-Application
timestamps	O
as	O
a	O
64-bit	B-Device
nanosecond	O
counter	O
instead	O
of	O
the	O
traditional	O
32-bit	O
seconds	O
counter	O
.	O
</s>
<s>
This	O
postpones	O
the	O
previous	O
Year	B-Application
2038	I-Application
problem	I-Application
until	O
the	O
year	O
2486	O
.	O
</s>
<s>
XFS	B-Application
is	O
a	O
64-bit	B-Device
file	O
system	O
and	O
supports	O
a	O
maximum	O
file	O
system	O
size	O
of	O
8	O
exbibytes	O
minus	O
one	O
byte	B-Application
(	O
263−	O
1	O
bytes	B-Application
)	O
,	O
but	O
limitations	O
imposed	O
by	O
the	O
host	O
operating	O
system	O
can	O
decrease	O
this	O
limit	O
.	O
</s>
<s>
32-bit	O
Linux	B-Operating_System
systems	O
limit	O
the	O
size	O
of	O
both	O
the	O
file	O
and	O
file	O
system	O
to	O
16	O
tebibytes	O
.	O
</s>
<s>
In	O
modern	O
computing	O
,	O
journaling	B-Application
is	O
a	O
capability	O
which	O
ensures	O
consistency	O
of	O
data	O
in	O
the	O
file	O
system	O
,	O
despite	O
any	O
power	O
outages	O
or	O
system	O
crash	O
that	O
may	O
occur	O
.	O
</s>
<s>
XFS	B-Application
provides	O
journaling	B-Application
for	O
file	O
system	O
metadata	O
,	O
where	O
file	O
system	O
updates	O
are	O
first	O
written	O
to	O
a	O
serial	O
journal	O
before	O
the	O
actual	O
disk	O
blocks	O
are	O
updated	O
.	O
</s>
<s>
The	O
XFS	B-Application
journal	O
can	O
be	O
stored	O
within	O
the	O
data	O
section	O
of	O
the	O
file	O
system	O
(	O
as	O
an	O
internal	O
log	O
)	O
,	O
or	O
on	O
a	O
separate	O
device	O
to	O
minimize	O
disk	O
contention	O
.	O
</s>
<s>
In	O
XFS	B-Application
,	O
the	O
journal	O
primarily	O
contains	O
entries	O
that	O
describe	O
the	O
portions	O
of	O
the	O
disk	O
blocks	O
changed	O
by	O
filesystem	O
operations	O
.	O
</s>
<s>
In	O
the	O
event	O
of	O
a	O
system	O
crash	O
,	O
file	O
system	O
operations	O
which	O
occurred	O
immediately	O
prior	O
to	O
the	O
crash	O
can	O
be	O
reapplied	O
and	O
completed	O
as	O
recorded	O
in	O
the	O
journal	O
,	O
which	O
is	O
how	O
data	O
stored	O
in	O
XFS	B-Application
file	O
systems	O
remain	O
consistent	O
.	O
</s>
<s>
XFS	B-Application
file	O
systems	O
are	O
internally	O
partitioned	O
into	O
allocation	B-Application
groups	I-Application
,	O
which	O
are	O
equally	O
sized	O
linear	O
regions	O
within	O
the	O
file	O
system	O
.	O
</s>
<s>
Files	B-Operating_System
and	O
directories	O
can	O
span	O
allocation	B-Application
groups	I-Application
.	O
</s>
<s>
Each	O
allocation	B-Application
group	I-Application
manages	O
its	O
own	O
inodes	B-Application
and	O
free	O
space	O
separately	O
,	O
providing	O
scalability	O
and	O
parallelism	O
so	O
multiple	O
threads	O
and	O
processes	O
can	O
perform	O
I/O	B-General_Concept
operations	I-General_Concept
on	O
the	O
same	O
file	O
system	O
simultaneously	O
.	O
</s>
<s>
This	O
architecture	O
helps	O
to	O
optimize	O
parallel	O
I/O	B-General_Concept
performance	O
on	O
systems	O
with	O
multiple	O
processors	O
and/or	O
cores	O
,	O
as	O
metadata	O
updates	O
can	O
also	O
be	O
parallelized	O
.	O
</s>
<s>
The	O
internal	O
partitioning	B-Application
provided	O
by	O
allocation	B-Application
groups	I-Application
can	O
be	O
especially	O
beneficial	O
when	O
the	O
file	O
system	O
spans	O
multiple	O
physical	O
devices	O
,	O
allowing	O
optimal	O
usage	O
of	O
throughput	O
of	O
the	O
underlying	O
storage	O
components	O
.	O
</s>
<s>
If	O
an	O
XFS	B-Application
file	O
system	O
is	O
to	O
be	O
created	O
on	O
a	O
striped	O
RAID	B-Architecture
array	I-Architecture
,	O
a	O
stripe	B-General_Concept
unit	O
can	O
be	O
specified	O
when	O
the	O
file	O
system	O
is	O
created	O
.	O
</s>
<s>
This	O
maximizes	O
throughput	O
by	O
ensuring	O
that	O
data	O
allocations	O
,	O
inode	B-Application
allocations	O
and	O
the	O
internal	O
log	O
(	O
the	O
journal	O
)	O
are	O
aligned	O
with	O
the	O
stripe	B-General_Concept
unit	O
.	O
</s>
<s>
Blocks	O
used	O
in	O
files	B-Operating_System
stored	O
on	O
XFS	B-Application
file	O
systems	O
are	O
managed	O
with	O
variable	O
length	O
extents	B-Application
where	O
one	O
extent	O
describes	O
one	O
or	O
more	O
contiguous	O
blocks	O
.	O
</s>
<s>
Block-oriented	O
file	O
systems	O
manage	O
space	O
allocation	O
with	O
one	O
or	O
more	O
block-oriented	O
bitmaps	O
;	O
in	O
XFS	B-Application
,	O
these	O
structures	O
are	O
replaced	O
with	O
an	O
extent	O
oriented	O
structure	O
consisting	O
of	O
a	O
pair	O
of	O
B+	O
trees	O
for	O
each	O
file	O
system	O
allocation	B-Application
group	I-Application
.	O
</s>
<s>
One	O
of	O
the	O
B+	O
trees	O
is	O
indexed	O
by	O
the	O
length	O
of	O
the	O
free	O
extents	B-Application
,	O
while	O
the	O
other	O
is	O
indexed	O
by	O
the	O
starting	O
block	O
of	O
the	O
free	O
extents	B-Application
.	O
</s>
<s>
This	O
dual	O
indexing	O
scheme	O
allows	O
for	O
the	O
highly	O
efficient	O
allocation	O
of	O
free	O
extents	B-Application
for	O
file	O
system	O
operations	O
.	O
</s>
<s>
XFS	B-Application
allows	O
file	O
systems	O
to	O
be	O
created	O
with	O
block	O
sizes	O
ranging	O
between	O
512bytes	O
and	O
64KB	O
,	O
allowing	O
the	O
file	O
system	O
to	O
be	O
tuned	O
for	O
the	O
expected	O
degree	O
of	O
usage	O
.	O
</s>
<s>
When	O
many	O
small	O
files	B-Operating_System
are	O
expected	O
,	O
a	O
small	O
block	O
size	O
would	O
typically	O
maximize	O
capacity	O
,	O
but	O
for	O
a	O
system	O
dealing	O
mainly	O
with	O
large	O
files	B-Operating_System
,	O
a	O
larger	O
block	O
size	O
can	O
provide	O
a	O
performance	O
efficiency	O
advantage	O
.	O
</s>
<s>
XFS	B-Application
makes	O
use	O
of	O
lazy	O
evaluation	O
techniques	O
for	O
file	O
allocation	O
.	O
</s>
<s>
When	O
a	O
file	O
is	O
written	O
to	O
the	O
buffer	O
cache	O
,	O
rather	O
than	O
allocating	O
extents	B-Application
for	O
the	O
data	O
,	O
XFS	B-Application
simply	O
reserves	O
the	O
appropriate	O
number	O
of	O
file	O
system	O
blocks	O
for	O
the	O
data	O
held	O
in	O
memory	O
.	O
</s>
<s>
This	O
improves	O
the	O
chance	O
that	O
the	O
file	O
will	O
be	O
written	O
in	O
a	O
contiguous	O
group	O
of	O
blocks	O
,	O
reducing	O
fragmentation	B-Application
problems	O
and	O
increasing	O
performance	O
.	O
</s>
<s>
XFS	B-Application
provides	O
a	O
64-bit	B-Device
sparse	O
address	O
space	O
for	O
each	O
file	O
,	O
which	O
allows	O
both	O
for	O
very	O
large	O
file	O
sizes	O
,	O
and	O
for	O
"	O
holes	O
"	O
within	O
files	B-Operating_System
in	O
which	O
no	O
disk	O
space	O
is	O
allocated	O
.	O
</s>
<s>
Where	O
the	O
size	O
of	O
the	O
allocation	O
map	O
is	O
too	O
large	O
for	O
it	O
to	O
be	O
stored	O
within	O
the	O
inode	B-Application
,	O
the	O
map	O
is	O
moved	O
into	O
a	O
B+	O
tree	O
which	O
allows	O
for	O
rapid	O
access	O
to	O
data	O
anywhere	O
in	O
the	O
64-bit	B-Device
address	O
space	O
provided	O
for	O
the	O
file	O
.	O
</s>
<s>
XFS	B-Application
provides	O
multiple	O
data	O
streams	O
for	O
files	B-Operating_System
;	O
this	O
is	O
made	O
possible	O
by	O
its	O
implementation	O
of	O
extended	B-Application
attributes	I-Application
.	O
</s>
<s>
Extended	B-Application
attributes	I-Application
stored	O
in	O
the	O
root	O
namespace	O
can	O
be	O
modified	O
only	O
by	O
the	O
superuser	O
,	O
while	O
attributes	O
in	O
the	O
user	O
namespace	O
can	O
be	O
modified	O
by	O
any	O
user	O
with	O
permission	O
to	O
write	O
to	O
the	O
file	O
.	O
</s>
<s>
Extended	B-Application
attributes	I-Application
can	O
be	O
attached	O
to	O
any	O
kind	O
of	O
XFS	B-Application
inode	B-Application
,	O
including	O
symbolic	O
links	O
,	O
device	O
nodes	O
,	O
directories	O
,	O
etc	O
.	O
</s>
<s>
The	O
attr	O
utility	O
can	O
be	O
used	O
to	O
manipulate	O
extended	B-Application
attributes	I-Application
from	O
the	O
command	O
line	O
,	O
and	O
the	O
xfsdump	O
and	O
xfsrestore	O
utilities	O
are	O
aware	O
of	O
extended	B-Application
attributes	I-Application
,	O
and	O
will	O
back	O
up	O
and	O
restore	O
their	O
contents	O
.	O
</s>
<s>
Most	O
other	O
backup	O
systems	O
do	O
not	O
support	O
working	O
with	O
extended	B-Application
attributes	I-Application
.	O
</s>
<s>
For	O
applications	O
requiring	O
high	O
throughput	O
to	O
disk	O
,	O
XFS	B-Application
provides	O
a	O
direct	O
I/O	B-General_Concept
implementation	O
that	O
allows	O
non-cached	O
I/O	B-General_Concept
operations	I-General_Concept
to	O
be	O
applied	O
directly	O
to	O
the	O
userspace	O
.	O
</s>
<s>
Data	O
is	O
transferred	O
between	O
the	O
buffer	O
of	O
the	O
application	O
and	O
the	O
disk	O
using	O
DMA	B-General_Concept
,	O
which	O
allows	O
access	O
to	O
the	O
full	O
I/O	B-General_Concept
bandwidth	O
of	O
the	O
underlying	O
disk	O
devices	O
.	O
</s>
<s>
The	O
XFS	B-Application
guaranteed-rate	O
I/O	B-General_Concept
system	O
provides	O
an	O
API	O
that	O
allows	O
applications	O
to	O
reserve	O
bandwidth	O
to	O
the	O
filesystem	O
.	O
</s>
<s>
XFS	B-Application
dynamically	O
calculates	O
the	O
performance	O
available	O
from	O
the	O
underlying	O
storage	O
devices	O
,	O
and	O
will	O
reserve	O
bandwidth	O
sufficient	O
to	O
meet	O
the	O
requested	O
performance	O
for	O
a	O
specified	O
time	O
.	O
</s>
<s>
This	O
is	O
a	O
feature	O
unique	O
to	O
the	O
XFS	B-Application
file	O
system	O
.	O
</s>
<s>
Guaranteed	O
rates	O
can	O
be	O
"	O
hard	O
"	O
or	O
"	O
soft	O
"	O
,	O
representing	O
a	O
trade	O
off	O
between	O
reliability	O
and	O
performance	O
;	O
however	O
,	O
XFS	B-Application
will	O
only	O
allow	O
"	O
hard	O
"	O
guarantees	O
if	O
the	O
underlying	O
storage	O
subsystem	O
supports	O
it	O
.	O
</s>
<s>
Guaranteed-rate	O
I/O	B-General_Concept
was	O
only	O
supported	O
under	O
IRIX	B-Operating_System
,	O
and	O
required	O
special	O
hardware	O
for	O
that	O
purpose	O
.	O
</s>
<s>
XFS	B-Application
implemented	O
the	O
DMAPI	B-General_Concept
interface	O
to	O
support	O
Hierarchical	B-Application
Storage	I-Application
Management	I-Application
in	O
IRIX	B-Operating_System
.	O
</s>
<s>
As	O
of	O
October	O
2010	O
,	O
the	O
Linux	B-Operating_System
implementation	O
of	O
XFS	B-Application
supported	O
the	O
required	O
on-disk	O
metadata	O
for	O
DMAPI	B-General_Concept
implementation	O
,	O
but	O
the	O
kernel	B-Operating_System
support	O
was	O
reportedly	O
not	O
usable	O
.	O
</s>
<s>
For	O
some	O
time	O
,	O
SGI	O
hosted	O
a	O
kernel	B-Operating_System
tree	O
which	O
included	O
the	O
DMAPI	B-General_Concept
hooks	O
,	O
but	O
this	O
support	O
has	O
not	O
been	O
adequately	O
maintained	O
,	O
although	O
kernel	B-Operating_System
developers	O
have	O
stated	O
an	O
intention	O
to	O
bring	O
this	O
support	O
up	O
to	O
date	O
.	O
</s>
<s>
XFS	B-Application
does	O
not	O
yet	O
provide	O
direct	O
support	O
for	O
snapshots	B-Application
,	O
as	O
it	O
currently	O
expects	O
the	O
snapshot	B-Application
process	O
to	O
be	O
implemented	O
by	O
the	O
volume	O
manager	O
.	O
</s>
<s>
Taking	O
a	O
snapshot	B-Application
of	O
an	O
XFS	B-Application
filesystem	O
involves	O
temporarily	O
halting	O
I/O	B-General_Concept
to	O
the	O
filesystem	O
using	O
the	O
xfs_freeze	O
utility	O
,	O
having	O
the	O
volume	O
manager	O
perform	O
the	O
actual	O
snapshot	B-Application
,	O
and	O
then	O
resuming	O
I/O	B-General_Concept
to	O
continue	O
with	O
normal	O
operations	O
.	O
</s>
<s>
The	O
snapshot	B-Application
can	O
then	O
be	O
mounted	O
read-only	O
for	O
backup	O
purposes	O
.	O
</s>
<s>
Releases	O
of	O
XFS	B-Application
in	O
IRIX	B-Operating_System
incorporated	O
an	O
integrated	O
volume	O
manager	O
called	O
XLV	O
.	O
</s>
<s>
This	O
volume	O
manager	O
has	O
not	O
been	O
ported	O
to	O
Linux	B-Operating_System
,	O
and	O
XFS	B-Application
works	O
with	O
standard	O
LVM	B-Application
in	O
Linux	B-Operating_System
systems	O
instead	O
.	O
</s>
<s>
In	O
recent	O
Linux	B-Operating_System
kernels	I-Operating_System
,	O
the	O
xfs_freeze	O
functionality	O
is	O
implemented	O
in	O
the	O
VFS	O
layer	O
,	O
and	O
is	O
executed	O
automatically	O
when	O
the	O
Volume	O
Manager	O
's	O
snapshot	B-Application
functionality	O
is	O
invoked	O
.	O
</s>
<s>
This	O
was	O
once	O
a	O
valuable	O
advantage	O
as	O
the	O
ext3	B-Application
file	O
system	O
could	O
not	O
be	O
suspended	O
and	O
the	O
volume	O
manager	O
was	O
unable	O
to	O
create	O
a	O
consistent	O
"	O
hot	O
"	O
snapshot	B-Application
to	O
back	O
up	O
a	O
heavily	O
busy	O
database	O
.	O
</s>
<s>
Since	O
Linux	O
2.6.29	O
,	O
the	O
file	O
systems	O
ext3	B-Application
,	O
ext4	B-Application
,	O
GFS2	B-Application
and	O
JFS	B-Application
have	O
the	O
freeze	O
feature	O
as	O
well	O
.	O
</s>
<s>
Although	O
the	O
extent-based	O
nature	O
of	O
XFS	B-Application
and	O
the	O
delayed	B-Application
allocation	I-Application
strategy	O
it	O
uses	O
significantly	O
improves	O
the	O
file	O
system	O
's	O
resistance	O
to	O
fragmentation	B-Application
problems	O
,	O
XFS	B-Application
provides	O
a	O
filesystem	O
defragmentation	B-Application
utility	O
(	O
xfs_fsr	O
,	O
short	O
for	O
XFS	B-Application
filesystem	O
reorganizer	O
)	O
that	O
can	O
defragment	B-Application
the	O
files	B-Operating_System
on	O
a	O
mounted	O
and	O
active	O
XFS	B-Application
filesystem	O
.	O
</s>
<s>
XFS	B-Application
provides	O
the	O
xfs_growfs	O
utility	O
to	O
perform	O
online	O
expansion	O
of	O
XFS	B-Application
file	O
systems	O
.	O
</s>
<s>
XFS	B-Application
filesystems	O
can	O
be	O
grown	O
so	O
long	O
as	O
there	O
is	O
remaining	O
unallocated	O
space	O
on	O
the	O
device	O
holding	O
the	O
filesystem	O
.	O
</s>
<s>
This	O
feature	O
is	O
typically	O
used	O
in	O
conjunction	O
with	O
volume	O
management	O
,	O
as	O
otherwise	O
the	O
partition	B-Application
holding	O
the	O
filesystem	O
will	O
need	O
enlarging	O
separately	O
.	O
</s>
<s>
XFS	B-Application
filesystems	O
cannot	O
(	O
)	O
be	O
shrunk	O
in	O
place	O
,	O
although	O
several	O
possible	O
workarounds	O
have	O
been	O
discussed	O
.	O
</s>
<s>
Metadata	O
operations	O
in	O
XFS	B-Application
were	O
slower	O
compared	O
to	O
journaling	B-Application
file	I-Application
systems	I-Application
implemented	O
later	O
and	O
designed	O
to	O
work	O
with	O
much	O
larger	O
logs	O
resulting	O
in	O
,	O
for	O
example	O
,	O
slower	O
performance	O
with	O
operations	O
such	O
as	O
deletions	O
of	O
large	O
numbers	O
of	O
files	B-Operating_System
.	O
</s>
<s>
However	O
,	O
a	O
new	O
XFS	B-Application
feature	O
implemented	O
by	O
John	O
Nelson	O
and	O
called	O
delayed	O
logging	O
,	O
available	O
since	O
version	O
2.6.39	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
mainline	O
,	O
is	O
said	O
to	O
resolve	O
this	O
;	O
performance	O
benchmarks	O
done	O
by	O
the	O
developer	O
in	O
2010	O
revealed	O
performance	O
levels	O
to	O
be	O
similar	O
to	O
ext4	B-Application
at	O
low	O
thread	O
counts	O
,	O
and	O
superior	O
at	O
high	O
thread	O
counts	O
.	O
</s>
<s>
Journaling	B-Application
cannot	O
be	O
disabled	O
.	O
</s>
<s>
However	O
,	O
XFS	B-Application
can	O
write	O
to	O
an	O
external	O
journal	O
on	O
a	O
separate	O
block	O
device	O
instead	O
.	O
</s>
