Recommended spares pool size?

Discussion in 'Cisco' started by dexx, Aug 29, 2005.

  1. dexx

    dexx Guest

    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.
     
    dexx, Aug 29, 2005
    #1
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  2. 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.
    --
    'The short version of what Walter said is "You have asked a question
    which has no useful answer, please reconsider the nature of the
    problem you wish to solve".' -- Tony Mantler
     
    Walter Roberson, Aug 29, 2005
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  3. dexx

    stephen Guest

    "dexx" <> wrote in message
    news:...
    > 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.


    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.

    > 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.


    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.
    --
    Regards

    Stephen Hope - return address needs fewer xxs
     
    stephen, Aug 29, 2005
    #3
  4. 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:

    http://www.bradreese.com/cisco-big-iron-repair.htm

    The Cisco SMARTnet Pricing Calculator:

    http://www.bradreese.com/cisco-smartnet.htm

    Sincerely,

    Brad Reese
    BradReese.Com Cisco Repair Service Experts
    http://www.bradreese.com/index.htm#EXPERTS
    1293 Hendersonville Road, Suite 17
    Asheville, North Carolina USA 28803
    USA/Canada: 877-549-2680
    International: 828-277-7272
    United Kingdom: 44-20-70784294
     
    www.BradReese.Com, Aug 29, 2005
    #4
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