  This paper presents a measurement-based availability assessment study using
field data collected during a 4-year period from 373 SunOS/Solaris Unix
workstations and servers interconnected through a local area network. We focus
on the estimation of machine uptimes, downtimes and availability based on the
identification of failures that caused total service loss. Data corresponds to
syslogd event logs that contain a large amount of information about the normal
activity of the studied systems as well as their behavior in the presence of
failures. It is widely recognized that the information contained in such event
logs might be incomplete or imperfect. The solution investigated in this paper
to address this problem is based on the use of auxiliary sources of data
obtained from wtmpx files maintained by the SunOS/Solaris Unix operating
system. The results obtained suggest that the combined use of wtmpx and syslogd
log files provides more complete information on the state of the target systems
that is useful to provide availability estimations that better reflect reality.
