def compute(self, period=YEAR, mult=1):
""" probability of survival for an arbitrary object
period -- time period over which to estimate failures
mult -- FIT rate multiplier
"""
self.P_site = float(1) - Pfail(self.fits * mult, period, n=0)
self.L_site = self.size
self.dur = 1.0 - self.P_site
def compute(self, period=YEAR, mult=1, secondary=False):
""" compute probabilities and expected data loss for likely failures
period -- time over which we want to model failures
mult -- FIT rate multiplier (e.g. many parallel units)
secondary -- this is a second (more likely) failure
"""
fits = self.fits2 if secondary else self.fits
self.P_drive = float(1) - Pfail(fits * mult, period, n=0)
self.L_drive = self.size
self.P_nre = self.p_nre(bytes=self.size * mult)
self.L_nre = self.size
self.dur = 1.0 - (self.P_drive + self.P_nre)
def availability(self):
""" fraction of the time during which a remote copy is available """
# if we are ignoring failures, availability is 100%
if self.fits == 0:
return 1.0
# if there is no repair, annual probability of non-failure
if self.replace == 0:
return Pfail(self.fits, YEAR, n=0)
# one minus the time between failures and repair
ttf = mttf(self.fits)
return float(ttf) / (ttf + self.replace)