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<TITLE>RE: Quick Question on Industry Standard</TITLE>
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<P><FONT SIZE=2>-----Original Message-----</FONT>
<BR><FONT SIZE=2>From: K. Graham [<A HREF="mailto:kgraham@rogers.com">mailto:kgraham@rogers.com</A>]</FONT>
<BR><FONT SIZE=2>Sent: Saturday, April 06, 2002 6:26 AM</FONT>
<BR><FONT SIZE=2>To: nanog@merit.edu</FONT>
<BR><FONT SIZE=2>Subject: Quick Question on Industry Standard</FONT>
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<P><FONT SIZE=2>From my understanding there is a 99.97% up time value that most companies try </FONT>
<BR><FONT SIZE=2>and match. Is this a hard and fast rule or is this a value that we all try </FONT>
<BR><FONT SIZE=2>and emulate as best as we can? Do I have the value incorrect? Is it higher </FONT>
<BR><FONT SIZE=2>or lower? I had always thought that it was 99.97% but have not found </FONT>
<BR><FONT SIZE=2>anywhere to reference that figure, </FONT>
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<P><FONT SIZE=2>Cisco references that figure in their MTBF/MTTR (mean time before failure) calculations, however they also reference 99.9%. Our organization does not include scheduled maintenance in our HA (high availability) calculations, and I expect most organizations don't either.</FONT></P>
<P><FONT SIZE=2>Quote, "Availability is calculated using statistical models for all the system components, the simplest model for a component being binary. The component is either in or out of service. Availability can be calculated from failure rates, measured in mean time between failures (MTBF), and repair times, measured in mean time to repair (MTTR)."</FONT></P>
<P><FONT SIZE=2>Also, "The average downtime contribution by any component is calculated by amortizing the MTTR time over the MTBF period. For example, if a component critical to the operation of the platform has an MTBF of 250,000 hours and a MTTR of 1 hour, it contributes 2.1 minutes (60 min/250,000 hr/8760 hr/yr) of unavailability to the system per year"</FONT></P>
<P><FONT SIZE=2><A HREF="http://www.cisco.com/warp/public/cc/pd/rt/7500/prodlit/haibd_ov.htm" TARGET="_blank">http://www.cisco.com/warp/public/cc/pd/rt/7500/prodlit/haibd_ov.htm</A></FONT>
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<P><FONT SIZE=2>So to calculate the physical HA stats, you need to reduce your network to component levels and do the calculations. Cables are not usually included in these calculations.</FONT></P>
<P><FONT SIZE=2>HTH</FONT>
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<P><FONT SIZE=2>-- Tim</FONT>
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