[46610] in North American Network Operators' Group
RE: Quick Question on Industry Standard
daemon@ATHENA.MIT.EDU (Tim Devries)
Sat Apr 6 09:34:13 2002
Message-ID: <05924A4A9DEDAD46A21EE3C8C64B090DF3B941@cheetah.zoo.q9networks.com>
From: Tim Devries <Tim.Devries@Q9.com>
To: "'kgraham@ican.net'" <kgraham@ican.net>, nanog@merit.edu
Date: Sat, 6 Apr 2002 09:33:47 -0500
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-----Original Message-----
From: K. Graham [mailto:kgraham@rogers.com]
Sent: Saturday, April 06, 2002 6:26 AM
To: nanog@merit.edu
Subject: Quick Question on Industry Standard
From my understanding there is a 99.97% up time value that most companies
try
and match. Is this a hard and fast rule or is this a value that we all try
and emulate as best as we can? Do I have the value incorrect? Is it higher
or lower? I had always thought that it was 99.97% but have not found
anywhere to reference that figure,
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.
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)."
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"
http://www.cisco.com/warp/public/cc/pd/rt/7500/prodlit/haibd_ov.htm
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.
HTH
-- Tim
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<TITLE>RE: Quick Question on Industry Standard</TITLE>
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<P><FONT SIZE=3D2>-----Original Message-----</FONT>
<BR><FONT SIZE=3D2>From: K. Graham [<A =
HREF=3D"mailto:kgraham@rogers.com">mailto:kgraham@rogers.com</A>]</FONT>=
<BR><FONT SIZE=3D2>Sent: Saturday, April 06, 2002 6:26 AM</FONT>
<BR><FONT SIZE=3D2>To: nanog@merit.edu</FONT>
<BR><FONT SIZE=3D2>Subject: Quick Question on Industry Standard</FONT>
</P>
<BR>
<BR>
<P><FONT SIZE=3D2>From my understanding there is a 99.97% up time value =
that most companies try </FONT>
<BR><FONT SIZE=3D2>and match. Is this a hard and fast rule or is =
this a value that we all try </FONT>
<BR><FONT SIZE=3D2>and emulate as best as we can? Do I have the =
value incorrect? Is it higher </FONT>
<BR><FONT SIZE=3D2>or lower? I had always thought that it was =
99.97% but have not found </FONT>
<BR><FONT SIZE=3D2>anywhere to reference that figure, </FONT>
</P>
<BR>
<P><FONT SIZE=3D2>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=3D2>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=3D2>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=3D2><A =
HREF=3D"http://www.cisco.com/warp/public/cc/pd/rt/7500/prodlit/haibd_ov.=
htm" =
TARGET=3D"_blank">http://www.cisco.com/warp/public/cc/pd/rt/7500/prodlit=
/haibd_ov.htm</A></FONT>
</P>
<P><FONT SIZE=3D2>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=3D2>HTH</FONT>
</P>
<P><FONT SIZE=3D2>-- Tim</FONT>
</P>
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