<s>
In	O
a	O
distributed	B-Architecture
system	I-Architecture
,	O
failure	B-Operating_System
transparency	I-Operating_System
refers	O
to	O
the	O
extent	O
to	O
which	O
errors	O
and	O
subsequent	O
recoveries	O
of	O
hosts	B-Application
and	O
services	O
within	O
the	O
system	O
are	O
invisible	O
to	O
users	O
and	O
applications	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
if	O
a	O
server	O
fails	O
,	O
but	O
users	O
are	O
automatically	O
redirected	O
to	O
another	O
server	O
and	O
never	O
notice	O
the	O
failure	O
,	O
the	O
system	O
is	O
said	O
to	O
exhibit	O
high	O
failure	B-Operating_System
transparency	I-Operating_System
.	O
</s>
<s>
Failure	B-Operating_System
transparency	I-Operating_System
is	O
one	O
of	O
the	O
most	O
difficult	O
types	O
of	O
transparency	O
to	O
achieve	O
since	O
it	O
is	O
often	O
difficult	O
to	O
determine	O
whether	O
a	O
server	O
has	O
actually	O
failed	O
,	O
or	O
whether	O
it	O
is	O
simply	O
responding	O
very	O
slowly	O
.	O
</s>
<s>
Additionally	O
,	O
it	O
is	O
generally	O
impossible	O
to	O
achieve	O
full	O
failure	B-Operating_System
transparency	I-Operating_System
in	O
a	O
distributed	B-Architecture
system	I-Architecture
since	O
networks	O
are	O
unreliable	O
.	O
</s>
<s>
There	O
is	O
also	O
usually	O
a	O
trade-off	O
between	O
achieving	O
a	O
high	O
level	O
of	O
failure	B-Operating_System
transparency	I-Operating_System
and	O
maintaining	O
an	O
adequate	O
level	O
of	O
system	O
performance	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
a	O
distributed	B-Architecture
system	I-Architecture
attempts	O
to	O
mask	O
a	O
transient	O
server	O
failure	O
by	O
having	O
the	O
client	O
try	O
to	O
contact	O
the	O
failed	O
server	O
multiple	O
times	O
,	O
performance	O
of	O
the	O
system	O
may	O
be	O
negatively	O
affected	O
.	O
</s>
