I solve replacement items (of many kinds) with a formula that works for small and large deployments. It works for everything from switches to toilet paper so I have used it for more than my day job. It can and can be expressed in a spreadsheet like this "=CEILING(N1*M1,1)" where N is a column with the calculated need and M is a rate at which you need spares, or it is consumed before your next purchase. The formula is sometimes calculated on a spreadsheet and sometimes it is just a rough estimate in my head. Here are some example starting values for the M column. Optionally you can add a field for the ceiling value to reflect things that are only available in quantities greater than one. For example 10 for hotdogs and 8 for hotdog buns. The formalization of this formula is adapted from one my manager used, so credit is due to David Allen.
- 1.1 for something like a new line of APs you don't already have a deployment of. This allows for 10 spares in a deployment of 100 in case some arrive DOA or I find a flaw in my plan after the order/ post install. I would be more conservative if I didn't think I was ever going to need that model of APs elsewhere, and just take the heat if I end up short. - 1.01 for the subsequent deployment of APs if spares are already on hand. - 1.1 for something that is mission critical but we only have a few of. - 1 for expensive things that have a high availability feature and are under a reasonably quick turnaround service/replacement contract. - 1.2 for items that we ran out of quickly last time we made an annual purchase. - 1.05 for inexpensive things that would save some time to have spares of, but are only a minor inconvenience if you run out. Modify the value for subsequent orders based on current inventory or if you find that the failure (or consumption) rate is higher than expected. Another reason to modify the value is if replacements can be found locally, or if you can count a similar model of item that you have spare of as a replacement. MTBF is another variable to consider. Using this formula also helps determine the support level because you can calculate what you need to make the cheaper support levels a better value with an acceptable and/or similar risk. Greg Briggs Network Manager Pacific Lutheran University On Tue, Feb 27, 2018 at 8:23 AM, Jeffrey D. Sessler <j...@scrippscollege.edu > wrote: > > - Look at the turn-around time for warranty replacement. The free > limited-lifetime may take longer than if the AP is under an extended > contract. > - Evaluate your deployment plan. If your deployment is coverage-based, > where the loss of a single AP could be devastating to clients, then keep > more spares. If you have a dense deployment where the loss of one or more > APs is of little consequence, keep less. > - Spares are technology collecting dust with the same life-cycle as > those in production. If you have 5000 APs and spare 2%, that’s 100 APs that > would likely cover a moderately sized building, and provide a lot of > in-fill. > - If you keep spares, make sure to cycle them into production i.e. > always install them into a new project, and put new APs back on the spare > shelf. > - When you upgrade controller code, pull those spares out and let them > upgrade too, then test that they still work. > > > > Jeff > > > > *From: *"wireless-lan@listserv.educause.edu" <WIRELESS-LAN@LISTSERV. > EDUCAUSE.EDU> on behalf of "Trinklein, Jason R" <trinkle...@cofc.edu> > *Reply-To: *"wireless-lan@listserv.educause.edu" <WIRELESS-LAN@LISTSERV. > EDUCAUSE.EDU> > *Date: *Monday, February 26, 2018 at 10:21 AM > *To: *"wireless-lan@listserv.educause.edu" <WIRELESS-LAN@LISTSERV. > EDUCAUSE.EDU> > *Subject: *[WIRELESS-LAN] Offline/Spare Gear Inventory Size > > > > Hi All, > > > > I’m curious to know the size of your spare gear inventories. Do you keep a > percentage of each model of AP in inventory, and what is your reasoning? > Storms? Last minute/emergency wireless coverage needs? > > > > What percentage of your live gear do you keep as offline inventory? (100 > live APs with 1 inventory AP = 1% offline inventory). > > > > With Xirrus, we had an offline inventory of more than 10% of live > inventory. We kept that inventory to cover the high failure rate of the > equipment, the incidence of hurricanes and lightning strikes in our area, > the broad range of AP models on campus, and last minute large events in low > coverage areas. > > > > We are evaluating the minimum offline inventory for our new Aruba gear as > we finish up the vendor switch. I have been thinking 1-2%, but I want to > see what you guys do first, and why. > > > > Thank you, > > -- > > *Jason Trinklein* > > *Wireless Engineering Manager* > > College of Charleston > > 81 St. Philip Street | Office 311D | Charleston, SC 29403 > <https://maps.google.com/?q=81+St.+Philip+Street+%7C+Office+311D+%7C+Charleston,+SC+29403&entry=gmail&source=g> > > trinkle...@cofc.edu | (843) 300–8009 <(843)%20300-8009> > > *DID YOU KNOW?* *The Princeton Review* selected the College of Charleston > as one of 50 schools focused on providing students with practical > experiences that take their academics to the next level. > > ********** Participation and subscription information for this EDUCAUSE > Constituent Group discussion list can be found at http://www.educause.edu/ > discuss. > ********** Participation and subscription information for this EDUCAUSE > Constituent Group discussion list can be found at http://www.educause.edu/ > discuss. > > ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/discuss.
