Recommended spares pool size?

One of our customers keeps a pool of spare switches (eg 2950) and routers (eg 2621) to support their fleet. Recently the pool has become very small compared to the number of devices it is intended to cover. Can anyone link me to a document which defines a recommended spares ratio? (eg one spare per X units in service)? I want to persuade the client in increase the spares pool.

Reply to
dexx
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In article , dexx wrote: :One of our customers keeps a pool of spare switches (eg 2950) and :routers (eg 2621) to support their fleet. Recently the pool has become :very small compared to the number of devices it is intended to cover. :Can anyone link me to a document which defines a recommended spares :ratio? (eg one spare per X units in service)? I want to persuade the :client in increase the spares pool.

Do they have records of deployment of spares? If so then a MTBF could be calculated, and from there you could calculate probabilities of having N fail within a certain period. Presuming that there are no correlations in the failures, such as electrical spikes taking out all the devices in one wing.

Pragmatically, the spares pool only has to be big enough to be able to cover the longest re-order (or repair) time that one could expect... if it is acceptable that at some point one will have to start replacing with the next model along because the models in use have gone out of stock. If one needs to cover the entire duration of a particular project (e.g., 5 years) with a particular piece of equipment because it has a property that might not be implemented in other equipment (e.g., it's not easy to find a real hub anymore), then one's spares strategy would be different.

Reply to
Walter Roberson

you need to define "small" in a bit more detail.

also is this one pool (ie. all devices are at 1 site), or are they spread geographically.

most places i come across this sort of sparing scheme it is backed up by a repair or hardware swap out arrangment - is there anything like this in place?

if there is, then the response from the backup will dictate how long the spares are needed for on failure, and therefore how long they have to be swapped in for and affect how many spares are needed.

if any of this involves an "official" reseller or maintainer for the kit then they should have access to MTBF info on the equipment

if you have the MTBF then you can use statistics to work out how many spares are needed for a given level of risk of running out (although the stats assume independent failures, so if you think that a power surge is likely then you probably need more spares).

1 other suggestion is that the spares should be powered up and monitored by the management system, and / or get formally checked periodically - spares dont do a lot of good if they are broken when you need them. it also helps if they are kept at the same code release as the working kit.
Reply to
stephen

Hi Dexx,

The insurance companies that we perform "Cisco Repair Work" for have given us a "rule-of-thumb" that 8% of Cisco Product will fail over a 3 year period.

That is why "Cisco Hot Swaps" can be effective in managing costs:

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The Cisco SMARTnet Pricing Calculator:

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Sincerely,

Brad Reese BradReese.Com Cisco Repair Service Experts

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Hendersonville Road, Suite 17 Asheville, North Carolina USA 28803 USA/Canada: 877-549-2680 International: 828-277-7272 United Kingdom: 44-20-70784294

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