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calcote
Contributor
Contributor

Interplay between Expandable Reservation and Limit

I've read a number of threads on this topic, none of which have clearly explained whether the Limit setting and the Expandable Reservation setting are evoke mutually exclusive behavior. If a limit is defined on a Resource Pool, does this limit prevent VMs from taking advantage of available parent Resource Pool resources despite having the Expandable Reservation enabled? In other words, is the Expandable Reservation setting only valid if a limit is not defined?

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vmroyale
Immortal
Immortal

Note: Discussion successfully moved from VMware vCenter™ to vMotion & Resource Management

Brian Atkinson | vExpert | VMTN Moderator | Author of "VCP5-DCV VMware Certified Professional-Data Center Virtualization on vSphere 5.5 Study Guide: VCP-550" | @vmroyale | http://vmroyale.com
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frankdenneman
Expert
Expert

A limit trumps a reservation.

An expandable reservation is nothing more than an ability for a resource pool to request "free" reserved resources from its parent.

That means that expandable reservation can be active and a limit can be active at the same time. However the resource pool can request "free" reserved resources up to the limit.

For example:

Resource pool expandable reservation is enabled

Resource pool is configured with 40 GB of memory reservation

Resource pool is configured with 80 GB of memory limit.

The resource pool will provide 40GB of memory to its child objects (resource pools and VMs) from its own pool that is backed by physical memory.

Any resource pool or VM inside the resource pool that has a memory reservation configured (also applicable to vm memory overhead reservation) is request to the resource pool, if the 40GB pool is depleted, the resource pool will request resources backed by physical memory (reserved) from its parent.

It can do this until it reaches the 80GB.

The resource pool cannot utilize more than 80GB of physical memory protected by a reservation.

Make sense?

Blogging: frankdenneman.nl Twitter: @frankdenneman Co-author: vSphere 4.1 HA and DRS technical Deepdive, vSphere 5x Clustering Deepdive series
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frankdenneman
Expert
Expert

I published an article on expandable reservations today.

Maybe its of any help: http://frankdenneman.nl/2013/02/12/expandable-reservation-on-resource-pools-how-does-it-work/

Blogging: frankdenneman.nl Twitter: @frankdenneman Co-author: vSphere 4.1 HA and DRS technical Deepdive, vSphere 5x Clustering Deepdive series
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JCL_MDOT
Contributor
Contributor

Hello Mr. Denneman,

I know this is a really old thread, I get an error when I try to send you a private message.

I have an idea related to resource groups, I started a thread here:  Resource group idea, looking for feedback

You have some really good blog posts on this topic that go much deeper than anything else I can find online, most of which just re-iterates the function of resource pools and shares and some of the most common mistakes.  So you seem like the person most likely to have an idea about this.

Thank you for your attention

-JCL

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