<s>
ReiserFS	B-Application
is	O
a	O
general-purpose	O
,	O
journaling	B-Application
file	I-Application
system	I-Application
initially	O
designed	O
and	O
implemented	O
by	O
a	O
team	O
at	O
Namesys	O
led	O
by	O
Hans	O
Reiser	O
and	O
licensed	O
under	O
GPLv2	O
.	O
</s>
<s>
Introduced	O
in	O
version	O
2.4.1	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
,	O
it	O
was	O
the	O
first	O
journaling	B-Application
file	I-Application
system	I-Application
to	O
be	O
included	O
in	O
the	O
standard	O
kernel	B-Operating_System
.	O
</s>
<s>
ReiserFS	B-Application
was	O
the	O
default	O
file	O
system	O
in	O
Novell	O
's	O
SUSE	O
Linux	B-Application
Enterprise	O
until	O
Novell	O
decided	O
to	O
move	O
to	O
ext3	B-Application
on	O
October	O
12	O
,	O
2006	O
,	O
for	O
future	O
releases	O
.	O
</s>
<s>
Namesys	O
considered	O
ReiserFS	B-Application
version	O
3.6	O
which	O
introduced	O
a	O
new	O
on-disk	O
format	O
allowing	O
bigger	O
filesizes	O
,	O
now	O
occasionally	O
referred	O
to	O
as	O
Reiser3	B-Application
,	O
as	O
stable	O
and	O
feature-complete	O
and	O
,	O
with	O
the	O
exception	O
of	O
security	O
updates	O
and	O
critical	O
bug	O
fixes	O
,	O
ceased	O
development	O
on	O
it	O
to	O
concentrate	O
on	O
its	O
successor	O
,	O
Reiser4	B-Application
.	O
</s>
<s>
ReiserFS	B-Application
is	O
currently	O
supported	O
on	O
Linux	B-Application
without	O
quota	O
support	O
.	O
</s>
<s>
It	O
has	O
been	O
discussed	O
for	O
removal	O
from	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
since	O
early	O
2022	O
due	O
to	O
a	O
lack	O
of	O
maintenance	O
upstream	O
,	O
and	O
technical	O
issues	O
inherent	O
to	O
the	O
filesystem	O
,	O
such	O
as	O
the	O
fact	O
it	O
suffers	O
from	O
the	O
year	B-Application
2038	I-Application
problem	I-Application
;	O
it	O
was	O
deprecated	O
in	O
Linux	B-Application
5.18	O
,	O
with	O
removal	O
planned	O
for	O
2025	O
.	O
</s>
<s>
At	O
the	O
time	O
of	O
its	O
introduction	O
,	O
ReiserFS	B-Application
offered	O
features	O
that	O
had	O
not	O
been	O
available	O
in	O
existing	O
Linux	B-Application
file	O
systems	O
.	O
</s>
<s>
Reiser4	B-Application
may	O
have	O
improved	O
this	O
by	O
packing	O
tails	O
where	O
it	O
does	O
not	O
negatively	O
affect	O
performance	O
.	O
</s>
<s>
ReiserFS	B-Application
stores	O
file	O
metadata	O
(	O
"	O
stat	O
items	O
"	O
)	O
,	O
directory	B-Application
entries	O
(	O
"	O
directory	B-Application
items	O
"	O
)	O
,	O
inode	B-Application
block	O
lists	O
(	O
"	O
indirect	O
items	O
"	O
)	O
,	O
and	O
tails	O
of	O
files	B-Operating_System
(	O
"	O
direct	O
items	O
"	O
)	O
in	O
a	O
single	O
,	O
combined	O
B+	O
tree	O
keyed	O
by	O
a	O
universal	O
object	O
ID	O
.	O
</s>
<s>
Directory	B-Application
items	O
with	O
too	O
many	O
entries	O
or	O
indirect	O
items	O
which	O
are	O
too	O
long	O
to	O
fit	O
into	O
a	O
node	O
spill	O
over	O
into	O
the	O
right	O
leaf	O
neighbour	O
.	O
</s>
<s>
Block	O
allocation	O
is	O
tracked	O
by	O
free	B-Application
space	I-Application
bitmaps	I-Application
in	O
fixed	O
locations	O
.	O
</s>
<s>
By	O
contrast	O
,	O
ext2	B-Application
and	O
other	O
Berkeley	O
FFS-like	O
file	O
systems	O
of	O
that	O
time	O
simply	O
used	O
a	O
fixed	O
formula	O
for	O
computing	O
inode	B-Application
locations	O
,	O
hence	O
limiting	O
the	O
number	O
of	O
files	B-Operating_System
they	O
may	O
contain	O
.	O
</s>
<s>
Most	O
such	O
file	O
systems	O
also	O
store	O
directories	B-Application
as	O
simple	O
lists	O
of	O
entries	O
,	O
which	O
makes	O
directory	B-Application
lookups	O
and	O
updates	O
linear	O
time	O
operations	O
and	O
degrades	O
performance	O
on	O
very	O
large	O
directories	B-Application
.	O
</s>
<s>
The	O
single	O
B+	O
tree	O
design	O
in	O
ReiserFS	B-Application
avoids	O
both	O
of	O
these	O
problems	O
due	O
to	O
better	O
scalability	O
properties	O
.	O
</s>
<s>
Compared	O
with	O
ext2	B-Application
and	O
ext3	B-Application
in	O
version	O
2.4	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
,	O
when	O
dealing	O
with	O
files	B-Operating_System
under	O
4KiB	O
and	O
with	O
tail	O
packing	O
enabled	O
,	O
ReiserFS	B-Application
may	O
be	O
faster	O
.	O
</s>
<s>
Before	O
Linux	O
2.6.33	O
,	O
ReiserFS	B-Application
heavily	O
used	O
the	O
big	B-Operating_System
kernel	I-Operating_System
lock	I-Operating_System
(	O
BKL	O
)	O
—	O
a	O
global	O
kernel-wide	O
lock	O
—	O
which	O
does	O
not	O
scale	O
well	O
for	O
systems	O
with	O
multiple	O
cores	O
,	O
as	O
the	O
critical	O
code	O
parts	O
are	O
only	O
ever	O
executed	O
by	O
one	O
core	O
at	O
a	O
time	O
.	O
</s>
<s>
ReiserFS	B-Application
was	O
the	O
default	O
file	O
system	O
in	O
SuSE	O
Linux	B-Application
since	O
version	O
6.4	O
(	O
released	O
in	O
2000	O
)	O
,	O
until	O
switching	O
to	O
ext3	B-Application
in	O
SUSE	O
Linux	B-Application
Enterprise	O
10.2	O
and	O
openSUSE	B-Operating_System
11	I-Operating_System
,	O
announced	O
in	O
2006	O
.	O
</s>
<s>
Jeff	O
Mahoney	O
of	O
SUSE	O
wrote	O
a	O
post	O
on	O
14	O
September	O
2006	O
proposing	O
to	O
move	O
from	O
ReiserFS	B-Application
to	O
ext3	B-Application
for	O
the	O
default	O
installation	O
file	O
system	O
.	O
</s>
<s>
Some	O
reasons	O
he	O
mentioned	O
were	O
scalability	O
,	O
"	O
performance	O
problems	O
with	O
extended	B-Application
attributes	I-Application
and	O
ACLs	O
"	O
,	O
"	O
a	O
small	O
and	O
shrinking	O
development	O
community	O
"	O
,	O
and	O
that	O
"	O
Reiser4	B-Application
is	O
not	O
an	O
incremental	O
update	O
and	O
requires	O
a	O
reformat	O
,	O
which	O
is	O
unreasonable	O
for	O
most	O
people.	O
"	O
</s>
<s>
Some	O
directory	B-Application
operations	O
(	O
including	O
(	O
2	O
)	O
)	O
are	O
not	O
synchronous	O
on	O
ReiserFS	B-Application
,	O
which	O
can	O
result	O
in	O
data	O
corruption	O
with	O
applications	O
relying	O
heavily	O
on	O
file-based	O
locks	O
(	O
such	O
as	O
mail	B-Protocol
transfer	I-Protocol
agents	I-Protocol
qmail	B-Application
and	O
Postfix	B-Application
)	O
if	O
the	O
machine	O
halts	O
before	O
it	O
has	O
synchronized	O
the	O
disk	O
.	O
</s>
<s>
There	O
are	O
no	O
programs	O
to	O
specifically	O
defragment	B-Application
a	O
ReiserFS	B-Application
file	O
system	O
,	O
although	O
tools	O
have	O
been	O
written	O
to	O
automatically	O
copy	O
the	O
contents	O
of	O
fragmented	O
files	B-Operating_System
hoping	O
that	O
more	O
contiguous	O
blocks	O
of	O
free	O
space	O
can	O
be	O
found	O
.	O
</s>
<s>
However	O
,	O
a	O
"	O
repacker	O
"	O
tool	O
was	O
planned	O
for	O
the	O
next	O
Reiser4	B-Application
file	O
system	O
to	O
deal	O
with	O
file	O
fragmentation	O
.	O
</s>
<s>
Fragmentation	O
is	O
still	O
an	O
issue	O
with	O
SSD	B-Device
regardless	O
of	O
file	O
system	O
.	O
</s>
<s>
ReiserFS	B-Application
3	O
's	O
fsck	B-Device
is	O
capable	O
to	O
rebuild	O
the	O
whole	O
tree	O
as	O
part	O
of	O
the	O
rescue	O
in	O
case	O
of	O
its	O
total	O
corruption	O
.	O
</s>
<s>
Predictably	O
,	O
the	O
process	O
is	O
destructive	O
and	O
may	O
further	O
corrupt	O
existing	O
files	B-Operating_System
or	O
introduce	O
new	O
entries	O
with	O
unexpected	O
contents	O
,	O
which	O
has	O
been	O
criticized	O
as	O
less	O
than	O
optimal	O
method	O
.	O
</s>
<s>
ReiserFS	B-Application
v3	O
images	O
should	O
not	O
be	O
stored	O
on	O
a	O
ReiserFS	B-Application
v3	O
partition	B-Application
(	O
e.g.	O
</s>
<s>
backups	O
or	O
disk	B-Application
images	I-Application
for	O
emulators	O
)	O
without	O
transforming	O
them	O
(	O
e.g.	O
,	O
by	O
compressing	O
or	O
encrypting	O
)	O
in	O
order	O
to	O
avoid	O
confusing	O
the	O
rebuild	O
.	O
</s>
<s>
Reformatting	O
an	O
existing	O
ReiserFS	B-Application
v3	O
partition	B-Application
can	O
also	O
leave	O
behind	O
data	O
that	O
could	O
confuse	O
the	O
rebuild	O
operation	O
and	O
make	O
files	B-Operating_System
from	O
the	O
old	O
system	O
reappear	O
.	O
</s>
<s>
This	O
also	O
allows	O
malicious	O
users	O
to	O
intentionally	O
store	O
files	B-Operating_System
that	O
will	O
confuse	O
the	O
rebuilder	O
.	O
</s>
<s>
As	O
the	O
metadata	O
is	O
always	O
in	O
a	O
consistent	O
state	O
after	O
a	O
file	O
system	O
check	O
,	O
corruption	O
here	O
means	O
that	O
contents	O
of	O
files	B-Operating_System
are	O
merged	O
in	O
unexpected	O
ways	O
with	O
the	O
contained	O
file	O
system	O
's	O
metadata	O
.	O
</s>
<s>
This	O
is	O
similar	O
to	O
the	O
FSID	O
problem	O
in	O
btrfs	B-Operating_System
.	O
</s>
<s>
The	O
ReiserFS	B-Application
successor	O
,	O
Reiser4	B-Application
,	O
fixes	O
this	O
problem	O
.	O
</s>
<s>
ReiserFS	B-Application
in	O
versions	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
before	O
2.4.16	O
were	O
considered	O
unstable	O
by	O
Namesys	O
and	O
not	O
recommended	O
for	O
production	O
use	O
,	O
especially	O
in	O
conjunction	O
with	O
NFS	B-Protocol
.	O
</s>
<s>
Early	O
implementations	O
of	O
ReiserFS	B-Application
(	O
prior	O
to	O
that	O
in	O
Linux	O
2.6.2	O
)	O
were	O
also	O
susceptible	O
to	O
out-of-order	O
write	O
hazards	O
.	O
</s>
<s>
But	O
the	O
current	O
journaling	O
implementation	O
in	O
ReiserFS	B-Application
is	O
now	O
on	O
par	O
with	O
that	O
of	O
ext3	B-Application
's	O
"	O
ordered	O
"	O
journaling	O
level	O
.	O
</s>
