Poll - Is Hot Add used agressivley?

[jrmunday]

Hi All,

I just wanted to get a feeling for how aggressively Hot add is used in the enterprise for production infrastructure? More memory that CPU.

I will obviously go though all the technical requirements, pros and cons for using this but would be interesed in any feedback of reasons why you use this feature or not.

Thanks in advance,

Jon

[schepp]

Hey Jon,

we don't use hot add (neither memory, nor CPU).

I'd say because it's fast to provision the ressource, but hard to get back if you provision too much ( you don't get ressources back - ever )

We want our internal users to really think about the sizing before ordering VMs. So not thinking about it and changing the requirements too often will be punished with downtime

Tim

[grasshopper]

Hot add all the way on everything.  This equates to quality of life for IT staff and happy customers.  The only time I scrutinize this option is when going above 8 vCPU in which case there are arguments to turn it off for better performance / stability in some cases.

[jrmunday]

Hi Tim

you don't get ressources back - ever

Yep, it's always the usual fight to claw back any over provisioned resources.

Downtime is always a massive coordination and communication effort for me as the administrator so I'm thinking of making my life easier and offering hot add to deal with MSSQL requirements as we try and virtualise 100%.

Thanks for the feedback.

Cheers,

Jon

[jrmunday]

Hi Mike,

This was exactly what I was thinking, including the 8 vCPU metric for NUMA reasons.

Thanks for the feedback.

Cheers,

Jon

[tomtom901]

There is some overhead associated with hot add, but it seems to fit well in a virtualize first strategy as it offers the scaleable solution that's needed in 2014.

[King_Robert]

The drawback of the Hot Add feature is you can not roll back the provisioned resources once you increased.

it is beneficial where you need to add the resources to some extent and where there you feel the resource requirement is increased in future but did not decreased.

in short it is beneficial on that environment where the chances of decreasing resources in future is very less.

[BenLiebowitz]

We don't use it here.  If the users knew we could do that, They'd ask for upgrades way more often!

[vThinkBeyondVM]

We use rarely as we plan our workloads properly. But all the time, we can not plan perfectly. Hence hot add is awesome feature

[martin_hosken]

There are a couple of reasons why the Hot-Add features shouldn't be enabled on your templates.  This is why VMware doesn't have these features enabled by default.

1) Operating System and Application Supportability, not all Operating Systems support hot-add.  Even if the OS supports it, to get any  benefit, the application itself needs to support hot-add too. For instance, Windows 2008 R2 Enterprise running SQL Server 2008. Additional changes in SQL are likely to be required.

2) Additional Memory Overhead, when you enable Hot-Add on the virtual machine, the amount of memory overhead that will be used to run that VM will increase.  For instance, in vSphere 5.1, the amount of memory overhead used when enabling Hot-Add will be equivalent to a VM that is configured with 64 vCPUs and 1TB of vRAM (the maximum virtual resources available for the VM). If enabled by default on your templates this small overhead will add up quickly.

3) vNUMA is disabled on the Virtual Machine when the Hot-Add feature is enabled on a virtual machine, vNUMA is automatically disabled - which by default is enabled on VMs that have 8 or more vCPUs configured.

So you have to consider these drawbacks when deciding your use cases.

[MikeF0209]

I use hot add for memory not CPU.  CPU ended up crashing a VM for me.

[jrmunday]

Hi Martin,

Thanks for this feedback. I was thinking of enabling this specifically on Windows 2008 R2 and above MSSQL servers, but as you clearly point out there are good reasons this needs to be carefully considered. We don't have templates in our environment as all provisioning is fully automated - slower to provision, but at least a global standard in workflows (including decommissioning process).

From all the responses so far, there also seems to be fairly mixed use cases and reasons for using this or not - perhaps the size of organisations is a key factor as well?

I think a full use case analysis is in order before any sensible decision can be made.

Thanks for all the feedback from other too.

Cheers,

Jon