<s>
The	O
Andrew	B-Application
File	I-Application
System	I-Application
(	O
AFS	O
)	O
is	O
a	O
distributed	B-Protocol
file	I-Protocol
system	I-Protocol
which	O
uses	O
a	O
set	O
of	O
trusted	O
servers	O
to	O
present	O
a	O
homogeneous	O
,	O
location-transparent	O
file	O
name	O
space	O
to	O
all	O
the	O
client	O
workstations	O
.	O
</s>
<s>
It	O
was	O
developed	O
by	O
Carnegie	O
Mellon	O
University	O
as	O
part	O
of	O
the	O
Andrew	B-Operating_System
Project	I-Operating_System
.	O
</s>
<s>
Its	O
primary	O
use	O
is	O
in	O
distributed	B-Architecture
computing	I-Architecture
.	O
</s>
<s>
AFS	O
has	O
several	O
benefits	O
over	O
traditional	O
networked	O
file	B-Application
systems	I-Application
,	O
particularly	O
in	O
the	O
areas	O
of	O
security	O
and	O
scalability	O
.	O
</s>
<s>
AFS	O
uses	O
Kerberos	B-Protocol
for	O
authentication	O
,	O
and	O
implements	O
access	O
control	O
lists	O
on	O
directories	O
for	O
users	O
and	O
groups	O
.	O
</s>
<s>
Each	O
client	O
caches	O
files	O
on	O
the	O
local	O
filesystem	B-Application
for	O
increased	O
speed	O
on	O
subsequent	O
requests	O
for	O
the	O
same	O
file	O
.	O
</s>
<s>
This	O
also	O
allows	O
limited	O
filesystem	B-Application
access	O
in	O
the	O
event	O
of	O
a	O
server	B-General_Concept
crash	I-General_Concept
or	O
a	O
network	O
outage	O
.	O
</s>
<s>
AFS	O
uses	O
the	O
Weak	B-General_Concept
Consistency	I-General_Concept
model	O
.	O
</s>
<s>
A	O
consequence	O
of	O
the	O
file	B-Application
locking	I-Application
strategy	O
is	O
that	O
AFS	O
does	O
not	O
support	O
large	O
shared	O
databases	O
or	O
record	O
updating	O
within	O
files	O
shared	O
between	O
client	O
systems	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
the	O
original	O
email	O
system	O
for	O
the	O
Andrew	B-Operating_System
Project	I-Operating_System
,	O
the	O
Andrew	O
Message	O
System	O
,	O
a	O
single	O
file	O
per	O
message	O
is	O
used	O
,	O
like	O
maildir	O
,	O
rather	O
than	O
a	O
single	O
file	O
per	O
mailbox	O
,	O
like	O
mbox	B-Application
.	O
</s>
<s>
A	O
significant	O
feature	O
of	O
AFS	O
is	O
the	O
volume	B-Application
,	O
a	O
tree	O
of	O
files	O
,	O
sub-directories	O
and	O
AFS	O
mountpoints	B-Application
(	O
links	O
to	O
other	O
AFS	O
volumes	O
)	O
.	O
</s>
<s>
files	O
as	O
usual	O
without	O
concern	O
for	O
the	O
physical	O
location	O
of	O
the	O
volume	B-Application
.	O
</s>
<s>
A	O
volume	B-Application
may	O
have	O
a	O
quota	B-Application
assigned	O
to	O
it	O
in	O
order	O
to	O
limit	O
the	O
amount	O
of	O
space	O
consumed	O
.	O
</s>
<s>
As	O
needed	O
,	O
AFS	O
administrators	O
can	O
move	O
that	O
volume	B-Application
to	O
another	O
server	O
and	O
disk	O
location	O
without	O
the	O
need	O
to	O
notify	O
users	O
;	O
the	O
operation	O
can	O
even	O
occur	O
while	O
files	O
in	O
that	O
volume	B-Application
are	O
being	O
used	O
.	O
</s>
<s>
When	O
accessing	O
files	O
in	O
a	O
read-only	O
volume	B-Application
,	O
a	O
client	O
system	O
will	O
retrieve	O
data	O
from	O
a	O
particular	O
read-only	O
copy	O
.	O
</s>
<s>
The	O
AFS	O
command	O
suite	O
guarantees	O
that	O
all	O
read-only	O
volumes	O
contain	O
exact	O
copies	O
of	O
the	O
original	O
read-write	O
volume	B-Application
at	O
the	O
time	O
the	O
read-only	O
copy	O
was	O
created	O
.	O
</s>
<s>
The	O
shared	O
name	O
space	O
(	O
usually	O
mounted	O
as	O
/afs	O
on	O
the	O
Unix	O
filesystem	B-Application
)	O
is	O
identical	O
on	O
all	O
workstations	O
.	O
</s>
<s>
The	O
Andrew	B-Application
File	I-Application
System	I-Application
heavily	O
influenced	O
Version	O
4	O
of	O
Sun	O
Microsystems	O
 '	O
popular	O
Network	B-Protocol
File	I-Protocol
System	I-Protocol
(	O
NFS	O
)	O
.	O
</s>
<s>
Additionally	O
,	O
a	O
variant	O
of	O
AFS	O
,	O
the	O
DCE	B-Protocol
Distributed	I-Protocol
File	I-Protocol
System	I-Protocol
(	O
DFS	B-Protocol
)	O
was	O
adopted	O
by	O
the	O
Open	B-Application
Software	I-Application
Foundation	I-Application
in	O
1989	O
as	O
part	O
of	O
their	O
Distributed	B-Operating_System
Computing	I-Operating_System
Environment	I-Operating_System
.	O
</s>
<s>
Finally	O
AFS	O
(	O
version	O
two	O
)	O
was	O
the	O
predecessor	O
of	O
the	O
Coda	B-Application
file	B-Application
system	I-Application
.	O
</s>
<s>
OpenAFS	B-Application
was	O
built	O
from	O
source	O
released	O
by	O
Transarc	O
(	O
IBM	O
)	O
in	O
2000	O
.	O
</s>
<s>
A	O
fourth	O
implementation	O
of	O
an	O
AFS	O
client	O
exists	O
in	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
source	O
code	O
since	O
at	O
least	O
version	O
2.6.10	O
.	O
</s>
<s>
allows	O
the	O
processor	O
to	O
run	O
programs	O
that	O
need	O
to	O
"	O
flock	B-Application
"	O
files	O
in	O
the	O
directory	O
.	O
</s>
