HA/DRS: Memory Usage Warnings

[BrennanB]

After reading some fo the memory management docs I am still not clear on the result of running hosts with a memory warning. At what point will HA fail?

I have the default settings for alarms so when memory usage on the host is above 75% for 5 minutes it warns and 90% it alerts. Right now 2 out of my 5 hosts run at 80% memory usage and a 3rd runs at 90%. I will be adding additional hosts next month but in the meantime.

I have always run hosts well below the point of this warning but a few Vm's were added while I was out on medical leave and I am having to convince others why running at these levels is a bad idea. I understand memory management but jsut not sure at whatpoint HA/DRS can fail.

[bilalhashmi]

I am not sure what you mean by at what point HA will fail? HA will not fail because of memory utilization. You can ovecommit as long as your host allows and ur cluster admission control setting permits.

If the host is under stress, DRS may move VMs to another host if they will better the performance of the VM. Also if that doesn't happen, depending on the state of your host memory (high, soft, low, hard), your VM will experience balooing, compression and swapping.. Also TPS is really what will allow u to overcommit enormoulsy... Overcommiting will not cause HA to fail. HA will continue to work as long as your HA agent is working and your cluster passes a sanity check..

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[DSTAVERT]

The question to ask yourself. If one host failed -- take your pick -- would the remaining hosts have enough resources to run the added VMs. It becomes especially dificult when you have different amounts of RAM in each host. 75% might be OK the more hosts you have to spread the load.

[bilalhashmi]

Also, I recommend you read this book co-authored by Duncan and Frank... its a must read for anyone who want to work with vSphere.. its great for everyone regardless of your level of knowledge about HA/DRS.. good luck..

http://www.cloud-buddy.com/?s=deep+&x=0&y=0

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