meghas1234
Contributor
Contributor

total no. of slots are lesser than used slots in a cluster

Hi All,

In our infrastructure, when i check "Advanced Runtime Info". I see total no. of slots are  lesser than used slots in cluster. In which scenari it it can b epossible to have more no. of used slots that total no.

HA Advanced Runtime Info:

Slot size                                  4000Mhz

                                               4 vCPUs,

                                                4232MB

Total Slots in Cluster                    16

Used Slots                                   66

Available Slots                              0

Total Powered on vms in Cluster     66

Total Hosts in cluster                      2

Total good host                               2

I'm new to this slots virtual environment so please help......

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11 Replies
Gkeerthy
Expert
Expert

see the below links for more info

http://www.yellow-bricks.com/2009/08/12/ha-and-slot-sizes/

http://virtualgeek.typepad.com/virtual_geek/2008/06/so-how-exactly.html

Please don't forget to award point for 'Correct' or 'Helpful', if you found the comment useful. (vExpert, VCP-Cloud. VCAP5-DCD, VCP4, VCP5, MCSE, MCITP)
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meghas1234
Contributor
Contributor

Thanks for your reply, but my question is still not answered. In which case, total slots are lesser than used slots.

or better , if you can explain me according to my scenario.

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depping
Leadership
Leadership

It probably means you added a reservation to a VM a while after all VMs were powered-on. So if you start with admission control on, you power on 500 VMs and then add a reservation that would only allow you to power-on 100 VMs this would be the result.

If you know power off a VM you won't be able to power it on any more.

Is there a reason the reservation is set this high?

I would prefer to use "percentage based admission control" in this case, to avoid skewing the numbers extreme.

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admin
Immortal
Immortal

HA computes the total number of slots by dividing each host capacity by the slot size and summing up. In your case, the slot size is very big presumably because your have one (or more) vms with very large reservations. The number of used slots is normally just the number of powered on vms (each vm uses 1 slot by default unless you put a cap on the slot size in which case some vms may require more than 1). Because of these definitions, it is possible for the used slots to be more than the total slots. If you're in this case it means that HA thinks there are not enough resources to guarantee failover of all vms. As you'll in the blog posts mentioned above, the slot algorithm can be overly conservative when you have outlier vms with much higher reservations than others.

Elisha

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meghas1234
Contributor
Contributor

Hi Deepss

Admission Control Polisy is Disabled in my scenario.

Current failover capacity is 0 hots

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depping
Leadership
Leadership

If admission control is disabled why are you concerned about this?

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krishna_v78
Enthusiast
Enthusiast

I guess meghas is looking for something else....

As said by others, Admission control calculates the slot size based on Reservation and then it decides how many slots can be accomodated assuming that remaining VMs will also be using the same reservation capacity.

For example:

4GB mem * 16 VMs = 64 GB of host memory. However, in your current scenario, all the VMs are not configured with 4GB mem along with Reservation, for that reason, used slot size = 66.

Hope this will clarify your question.

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meghas1234
Contributor
Contributor

Hi Krishna,

I understood how slots size and no. of slots are calculated but what I'm not able to understand is why it is showing  :

Total slots in cluster = 16 only and used slots = 66, available slots = 0.

I have 2 concerns here,

1) If we have disabled admission control policy, then how its calculating slots (just by taking the VM which is consuming max resorces? as I dont beleive we have any reservation on our VM's). Because there are VM's who are using 1 vpu and 1GB of memory also.

2) Total slots should be = Used slots + available slots ? is it so? Also in my situation Available slots are 0, so that means i can not powere on any new VM in this cluster?

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depping
Leadership
Leadership

meghas1234 wrote:

Hi Krishna,

I understood how slots size and no. of slots are calculated but what I'm not able to understand is why it is showing  :

Total slots in cluster = 16 only and used slots = 66, available slots = 0.

I have 2 concerns here,

1) If we have disabled admission control policy, then how its calculating slots (just by taking the VM which is consuming max resorces? as I dont beleive we have any reservation on our VM's). Because there are VM's who are using 1 vpu and 1GB of memory also.

2) Total slots should be = Used slots + available slots ? is it so? Also in my situation Available slots are 0, so that means i can not powere on any new VM in this cluster?

1) if you disable admission control there is no admission control calculation and even if it would show anything still... it is irrelevant as vCenter will not do anything with it. (can't test it right now, rebuilding my lab)

2) total slots = total amount of resources / slot size

3) if available slots are 0 you cannot power-on new VMs

Once again, if you have admission control disabled ... don't worry! If you have it enabled, take a look at RVTools and find out where that large slot size is coming from as you probably have a reservation set somewhere that you don't know about.

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depping
Leadership
Leadership

I just checked, but in my environment (5.0) when admission control is disabled it indeed shows the slotsize. This is however not used by vCenter for admission control is this is explicitly disabled.

So a couple of conclusions:

1) The slotsize mentioned is irrelevant for your environment when Admission Control is disabled

2) You do have a reservation set somewhere considering the slot size details. These are way more than just "overhead" numbers

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meghas1234
Contributor
Contributor

Thanks all...

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