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emmar
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Resource Pools and Expandable reservations

Ok, I'm not sure if this forum is the right forum for RPs seeing as they can exist on Hosts or Clusters...anywho.....

What i'm trying to understand is the impact to a parent RP once a child RP has taken some of the resources away from it... I understand all of the follwing scenario (taken from vmware doc):

1 Parent pool RPMOM has a reservation of 6GHz, and one running virtual machine

VMM1 that reserves 1GHz.

2 You create a child resource pool RPKID with a reservation of 2GHz and with

Expandable Reservation selected.

3 You add two virtual machines, VMK1 and VMK2, with reservations of 2GHz

each to the child resource pool and attempt to power them on.

NOTE Reservations are checked only when you power on a virtual machine.

4 VMK1 can reserve the resources directly from RPKID (which has 2GHz).

5 There are no local resources available for VMK2, so it borrows resources from the

parent resource pool, RPMOM. RPMOM has 6GHz minus 1GHz (reserved by the

virtual machine) minus 2GHz (reserved by RPKID), which leaves 3GHz

unreserved. With 3GHz available, you can power on the 2GHz virtual machine.[/i]

But what would happen now if i put a new VM in RPMOM called VMM2 with a reservation of 3GHz, as the RPKID resource pool has "expanded" into the availble resources of RPMOM, it only really has 1GHz left.....i'm presuming this means i cant power on my new VM (VMM2) as it's reservation cant be met (i'm also assuming that RPMOM doesnt have a parent pool and does not allow Expandable Reservation enabled) Is this right? It jsut seems a bit weird that a VM in the parent pool doesnt have some form of priority over it's resources as opposed to the child RP which has "borrowed" some.

I know in this example we're talking CPU so there is the possibility that CPU resources will become availble because if CPU reservation is idle, it can be borrowed by other VMs etc. But with memory, once the VM has attained its reservation, it's not giving it up whether it's idle or not....

Any thoughts on this?

Thanks All

Emma

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bflynn0
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But what would happen now if i put a new VM in RPMOM

called VMM2 with a reservation of 3GHz, as the RPKID

resource pool has "expanded" into the availble

resources of RPMOM, it only really has 1GHz

left.....i'm presuming this means i cant power on my

new VM (VMM2) as it's reservation cant be met (i'm

also assuming that RPMOM doesnt have a parent pool

and does not allow Expandable Reservation enabled)

Is this right? It jsut seems a bit weird that a VM

in the parent pool doesnt have some form of priority

over it's resources as opposed to the child RP which

has "borrowed" some.

You are correct VMM2 would not be able to be powered on. Basically the last VM to power on will lose out. Priority within Resource Pools would be an interesting concept. However since the reservations are only checked at power on and not continuously I'm not really sure it would be worth the effort. If you think about it, VMware has it implemented pretty well. They wouldn't have it so that a lower priority VM would power off just because you're powering on a VM with a higher priority, that'd be like taking down a workgroup application server already in production so you can fit a new large database server into a rack. Just like in the physical world implementing a new VM server should require planning and design (I did say should Smiley Wink ) At least in an ESX environment you can dynamically change the reservation of the RP. Just my 2 cents

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bflynn0
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But what would happen now if i put a new VM in RPMOM

called VMM2 with a reservation of 3GHz, as the RPKID

resource pool has "expanded" into the availble

resources of RPMOM, it only really has 1GHz

left.....i'm presuming this means i cant power on my

new VM (VMM2) as it's reservation cant be met (i'm

also assuming that RPMOM doesnt have a parent pool

and does not allow Expandable Reservation enabled)

Is this right? It jsut seems a bit weird that a VM

in the parent pool doesnt have some form of priority

over it's resources as opposed to the child RP which

has "borrowed" some.

You are correct VMM2 would not be able to be powered on. Basically the last VM to power on will lose out. Priority within Resource Pools would be an interesting concept. However since the reservations are only checked at power on and not continuously I'm not really sure it would be worth the effort. If you think about it, VMware has it implemented pretty well. They wouldn't have it so that a lower priority VM would power off just because you're powering on a VM with a higher priority, that'd be like taking down a workgroup application server already in production so you can fit a new large database server into a rack. Just like in the physical world implementing a new VM server should require planning and design (I did say should Smiley Wink ) At least in an ESX environment you can dynamically change the reservation of the RP. Just my 2 cents

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emmar
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Ahh the magic "planning and design" words!!

Thanks for the response, I can understand the reasoning behind it but just wanted to confirm that i'd fully understood the nature of the "expandable reservation". I know it would be wrong to auto power off the VM in the child pool, but wouldnt it be good if it could auto flag up an alert to show that the Child pool was now in "expanded" state so you were aware of the issue and could address it if necessary, before you decided to create a new VM in the parent pool.

Thanks again,

Emma

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