<s>
BitVault	B-Application
is	O
a	O
content-addressable	O
distributed	O
storage	O
system	O
,	O
developed	O
by	O
Microsoft	O
Research	O
in	O
China	O
.	O
</s>
<s>
BitVault	B-Application
uses	O
peer-to-peer	O
technology	O
to	O
distribute	O
the	O
tasks	O
of	O
storing	O
and	O
managing	O
data	O
.	O
</s>
<s>
Rather	O
,	O
it	O
is	O
self-managing	O
,	O
provides	O
high	O
availability	O
,	O
reliability	O
and	O
scales	O
up	O
in	O
a	O
self-organizing	O
manner	O
,	O
with	O
low	O
administrative	O
overhead	O
,	O
which	O
is	O
almost	O
constant	O
irrespective	O
of	O
the	O
size	O
of	O
the	O
distributed	O
overlay	B-Architecture
network	I-Architecture
.	O
</s>
<s>
BitVault	B-Application
system	O
is	O
best	O
suited	O
for	O
reference	O
data	O
,	O
which	O
is	O
large	O
amount	O
of	O
data	O
which	O
changes	O
very	O
infrequently	O
.	O
</s>
<s>
Every	O
participating	O
peer	O
node	O
in	O
BitVault	B-Application
architecture	O
is	O
a	O
Smart	O
Brick	O
,	O
which	O
is	O
a	O
trimmed	O
down	O
PC	O
with	O
large	O
disks	O
.	O
</s>
<s>
All	O
Smart	O
Bricks	O
in	O
a	O
BitVault	B-Application
system	O
are	O
connected	O
by	O
a	O
high-bandwidth	O
,	O
low	O
latency	O
network	B-Architecture
.	O
</s>
<s>
A	O
BitVault	B-Application
system	O
can	O
be	O
easily	O
scaled	O
up	O
–	O
any	O
computer	O
can	O
be	O
configured	O
to	O
act	O
as	O
a	O
Smart	O
Brick	O
by	O
simply	O
installing	O
the	O
BitVault	B-Application
software	O
,	O
and	O
connecting	O
it	O
to	O
the	O
network	B-Architecture
,	O
without	O
any	O
need	O
for	O
interrupting	O
the	O
already	O
working	O
nodes	O
.	O
</s>
<s>
BitVault	B-Application
stores	O
immutable	B-Application
data	O
objects	O
,	O
i.e.	O
,	O
objects	O
which	O
cannot	O
be	O
changed	O
.	O
</s>
<s>
To	O
get	O
around	O
this	O
problem	O
of	O
changing	O
locations	O
,	O
BitVault	B-Application
makes	O
it	O
accessible	O
by	O
means	O
of	O
a	O
160-bit	O
key	O
,	O
which	O
is	O
unique	O
for	O
each	O
object	O
.	O
</s>
<s>
Different	O
sets	O
of	O
nodes	O
maintain	O
different	O
sets	O
of	O
hash	O
tables	O
,	O
which	O
concern	O
with	O
only	O
the	O
data	O
in	O
that	O
set	O
of	O
nodes	O
,	O
thereby	O
giving	O
rise	O
to	O
an	O
overlay	B-Architecture
network	I-Architecture
in	O
which	O
the	O
location	O
of	O
the	O
data	O
is	O
tracked	O
by	O
a	O
distributed	B-Operating_System
hash	I-Operating_System
table	I-Operating_System
(	O
DHT	O
)	O
architecture	O
.	O
</s>
<s>
The	O
BitVault	B-Application
architecture	O
is	O
composed	O
of	O
multiple	O
bricks	O
which	O
constitute	O
a	O
logical	O
160	O
bit	O
address	O
space	O
,	O
each	O
associated	O
with	O
hash	O
of	O
some	O
data	O
.	O
</s>
<s>
The	O
association	O
is	O
maintained	O
in	O
a	O
Distributed	B-Operating_System
Hash	I-Operating_System
Table	I-Operating_System
(	O
DHT	O
)	O
.	O
</s>
<s>
Multiple	O
copies	O
of	O
a	O
single	O
object	O
,	O
called	O
replica	O
,	O
are	O
stored	O
in	O
the	O
BitVault	B-Application
system	O
,	O
to	O
give	O
enough	O
redundancy	B-General_Concept
.	O
</s>
<s>
The	O
MRL	O
uses	O
a	O
one	O
hop	O
DHT	O
to	O
perform	O
routing	O
,	O
i.e.	O
,	O
it	O
never	O
takes	O
more	O
than	O
one	O
hop	O
over	O
a	O
peer	O
to	O
route	O
messages	O
,	O
when	O
the	O
BitVault	B-Application
system	O
is	O
stable	O
,	O
i.e.	O
,	O
no	O
new	O
bricks	O
are	O
added	O
,	O
nor	O
is	O
any	O
load	O
balancing	O
or	O
repair	O
going	O
on	O
.	O
</s>
<s>
IM	O
listens	O
to	O
the	O
MRL	O
and	O
updates	O
itself	O
according	O
to	O
membership	O
changes	O
and	O
also	O
according	O
to	O
data	O
being	O
entered	O
into	O
BitVault	B-Application
system	O
or	O
being	O
retrieved	O
from	O
it	O
.	O
</s>
<s>
Along	O
with	O
the	O
object	O
,	O
its	O
metadata	O
such	O
as	O
its	O
hash	O
key	O
and	O
its	O
degree	O
of	O
replication	O
in	O
the	O
BitVault	B-Application
system	O
is	O
also	O
kept	O
.	O
</s>
<s>
Inserting	O
data	O
into	O
the	O
BitVault	B-Application
system	O
is	O
called	O
Check	O
In	O
.	O
</s>
<s>
Check	O
Out	O
is	O
the	O
process	O
of	O
retrieving	O
data	O
from	O
the	O
BitVault	B-Application
system	O
.	O
</s>
<s>
The	O
application	O
which	O
uses	O
BitVault	B-Application
as	O
its	O
datastore	O
gives	O
the	O
hash	O
key	O
of	O
the	O
object	O
to	O
be	O
retrieved	O
,	O
which	O
is	O
sent	O
by	O
the	O
MRL	O
to	O
any	O
brick	O
.	O
</s>
<s>
BitVault	B-Application
faults	O
can	O
be	O
either	O
transient	O
or	O
permanent	O
.	O
</s>
<s>
Whenever	O
a	O
new	O
brick	O
is	O
added	O
to	O
the	O
BitVault	B-Application
system	O
,	O
it	O
takes	O
up	O
a	O
random	O
ID	O
and	O
contacts	O
other	O
bricks	O
.	O
</s>
