<s>
Next3	B-Application
is	O
a	O
journaling	B-Application
file	I-Application
system	I-Application
for	O
Linux	B-Application
based	O
on	O
ext3	B-Application
which	O
adds	O
snapshots	B-Application
support	O
,	O
yet	O
retains	O
compatibility	O
to	O
the	O
ext3	B-Application
on-disk	O
format	O
.	O
</s>
<s>
Next3	B-Application
is	O
implemented	O
as	O
open-source	B-Application
software	I-Application
,	O
licensed	O
under	O
the	O
GPL	B-License
license	I-License
.	O
</s>
<s>
A	O
snapshot	B-Application
is	O
a	O
read-only	O
copy	O
of	O
the	O
file	O
system	O
frozen	O
at	O
a	O
point	O
in	O
time	O
.	O
</s>
<s>
Versioning	O
file	O
systems	O
like	O
Next3	B-Application
can	O
internally	O
track	O
old	O
versions	O
of	O
files	O
and	O
make	O
snapshots	B-Application
available	O
through	O
a	O
special	O
namespace	O
.	O
</s>
<s>
An	O
advantage	O
of	O
copy-on-write	B-Language
is	O
that	O
when	O
Next3	B-Application
writes	O
new	O
data	O
,	O
the	O
blocks	O
containing	O
the	O
old	O
data	O
can	O
be	O
retained	O
,	O
allowing	O
a	O
snapshot	B-Application
version	O
of	O
the	O
file	O
system	O
to	O
be	O
maintained	O
.	O
</s>
<s>
Next3	B-Application
snapshots	B-Application
are	O
created	O
quickly	O
,	O
since	O
all	O
the	O
data	O
composing	O
the	O
snapshot	B-Application
is	O
already	O
stored	O
;	O
they	O
are	O
also	O
space	O
efficient	O
,	O
since	O
any	O
unchanged	O
data	O
is	O
shared	O
among	O
the	O
file	O
system	O
and	O
its	O
snapshots	B-Application
.	O
</s>
<s>
The	O
traditional	O
Linux	B-Application
Logical	B-Application
Volume	I-Application
Manager	I-Application
volume	O
level	O
snapshots	B-Application
implementation	O
requires	O
that	O
storage	O
space	O
be	O
allocated	O
in	O
advance	O
.	O
</s>
<s>
Next3	B-Application
uses	O
Dynamically	O
provisioned	O
snapshots	B-Application
,	O
meaning	O
it	O
does	O
not	O
require	O
pre-allocation	O
of	O
storage	O
space	O
for	O
snapshots	B-Application
,	O
instead	O
allocating	O
space	O
as	O
it	O
is	O
needed	O
.	O
</s>
<s>
Storage	O
space	O
is	O
conserved	O
by	O
sharing	O
unchanged	O
data	O
among	O
the	O
file	O
system	O
and	O
its	O
snapshots	B-Application
.	O
</s>
<s>
Since	O
Next3	B-Application
aims	O
to	O
be	O
both	O
forward	B-General_Concept
and	O
backward	B-General_Concept
compatible	I-General_Concept
with	O
the	O
earlier	O
ext3	B-Application
,	O
all	O
of	O
the	O
on-disk	O
structures	O
are	O
identical	O
to	O
those	O
of	O
ext3	B-Application
.	O
</s>
<s>
The	O
file	O
system	O
can	O
be	O
mounted	O
for	O
read	O
by	O
existing	O
ext3	B-Application
implementations	O
with	O
no	O
modification	O
.	O
</s>
<s>
Because	O
of	O
that	O
,	O
Next3	B-Application
,	O
like	O
ext3	B-Application
,	O
lacks	O
a	O
number	O
of	O
features	O
of	O
more	O
recent	O
designs	O
,	O
such	O
as	O
extents	B-Application
.	O
</s>
<s>
When	O
there	O
are	O
no	O
snapshots	B-Application
,	O
Next3	B-Application
performance	O
is	O
equivalent	O
to	O
ext3	B-Application
performance	O
.	O
</s>
<s>
With	O
snapshots	B-Application
,	O
there	O
is	O
a	O
minor	O
overhead	O
per	O
write	O
of	O
metadata	O
block	O
(	O
copy-on-write	B-Language
)	O
and	O
a	O
smaller	O
overhead	O
(	O
~	O
1%	O
)	O
per	O
write	O
of	O
data	O
block	O
(	O
move-on-write	O
)	O
.	O
</s>
<s>
As	O
of	O
2011	O
,	O
Next4	O
,	O
a	O
project	O
for	O
porting	O
of	O
Next3	B-Application
snapshot	B-Application
capabilities	O
to	O
the	O
Ext4	B-Application
file	O
system	O
,	O
is	O
mostly	O
completed	O
.	O
</s>
