On 03/03/2014 01:35 PM, Joe Gordon wrote: > On Mon, Mar 3, 2014 at 10:01 AM, Zane Bitter <zbit...@redhat.com> wrote: >> On 03/03/14 12:32, Joe Gordon wrote: >>>> >>>>> - if you're reserving resources far before you'll need them, it'll be >>>>> cheaper >>> >>> Why? How does this save a provider money? >> >> >> If an operator has zero information about the level of future demand, they >> will have to spend a *lot* of money on excess capacity or risk running out. >> If an operator has perfect information about future demand, then they need >> spend no money on excess capacity. Everywhere in between, the amount of >> extra money they need to spend is a non-increasing function of the amount of >> information they have. QED. > > Sure. if an operator has perfect information about future demand they > won't need any excess capacity. But assuming you know some future > demand, how do you figure out how much of the future demand you know? > But sure I can see this as a potential money saver, but unclear by how > much. The Amazon model for this is a reservation is at minimum a year, > I am not sure how useful short term reservations would be in > determining future demand.
There are other useful things with reservations though. In a private
context the classic one is running number for close of business. Or
software team that's working towards a release might want to preallocate
resources for longer scale runs during a particular week.
Reservation can really be about global policy giving some tenants more
priority in getting resources than others (because you pre-allocate them).
I also know that with a lot of the HPC teams using OpenStack, this is a
fundamental part of scheduling. Not just the when, but the how long.
Having systems automatically get reaped after a certain amount of time
is something they very much want.
So I think the general idea have merrit. I just think we need to make
sure it integrates well with the rest of OpenStack, which I believe
means strong coupling to the scheduler.
-Sean
--
Sean Dague
Samsung Research America
s...@dague.net / sean.da...@samsung.com
http://dague.net
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