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AllBlack
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Memory usage in vCOPS v OS

Hi,

I am taking my first steps with vCOPS and it confirms what I always have known. We wasting resources.

The big problem is convining people that they don't need it!

Today someone asked to increase their SQL VM from 20GB to 40GB because of slow performance.
It is now up to me to proof that they don't need it.

vCOPS is actually recommending 5.5GB. Current demand is about 3.5GB. I have 3 months worth of data and I'd say it averages around the recommended number. In short I see nothing wrong in vCOPS.

Within Windows it is pretty much showing as using all its memory. The developer takes this as a sign of memory shortage.

My question is how do you convince the non-believers? I can show all the fancy graphs but they still think they know better.

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vcpguy
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It is going to be a tough call. If someone decides not to believe, then there isn't much you can do.

what kind of license do you have ? I think, having a charge back model, even though you don't implement any financial transaction, goes a long way helping users to understand, that they are hoarding resources.

involve management and show them the money that is being wasted.

show them historic usage, that may convinced

try to show them memory usage via esxtop, that might convince them...

try to show performane analysis from vsphere client.

check to see the health of the sql vm and when are they seeing this issue, may be a noisy neighbor problem.

These are he few things that I can think of. Hope this helps.

thanks

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admin
Immortal
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Hi,

We get this questions a lot and is very common. App owners want more resources as they look inside the OS and see that all memory is used...so we need to add more. The sad part is that that is 99% of the time this is not the case and by adding more resource one sometimes just make the issue worse. This is why we have the Demand model. It looks at the demand for resources.

Lets take your issue. You have an app owner that looks inside at his OS and sees no free memory. Two things from this:

1. SQL have been set to use all Memory. Yes you can set SQL to say use 5Gb and then you will see inside the OS 15Gb free memory suddenly. So even if you give it 40..SQL will take that again and OS will show no memory free...will the app owner then ask for more again ?

2. Have a look at your OS page file swop out rate. If that is being used a lot then you know you have a memory shortage. Thus the indication from with in the OS that there is a memory shortage is that your page file swop out rate will be high.

If they complaining about Slow performance you need to look at all aspects...VM Perforance/config/numa nodes/Hosts stats/disk/Network/....list is long...sadly.

vC Ops will show u which resource is the most in Demand...maybe start there.

Hope that helps.

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AllBlack
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Thanks,

Pretty much what I have been doing.

Sql is actually set to use 8GB but AFAIK windows 2008 caches the memory as well.

I will increase the RAM to proof a point. I am expecting the OS to show that is using all the additional memory indeed.

I checked the swap out rate in vcops and that was all fine. I will double check from within OS.

I am not disputing performance issues in this case as I did spot a few times a 100% disk workload. I am now waiting to hear from owner what times he experienced issues so I can compare it with reported  workloads in vcops.  I just need to get across that more RAM will not solve this.

vCOPS is a great tool but it does not take care of the politics you have to deal with 🙂

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admin
Immortal
Immortal

Hi,

Also look at your disk latency stats...sound more like you have a storage issue.

From a SQL perspective...look at cache hit rate....the hight that is the better indication that you might not need a memory increase. If you increase the memory on SQL you might then get rid of your disk issue as most of the data is then cached....so rather get to the bottom of the issue.(sounds like disk)

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AllBlack
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Expert

So we add a bit more RAM. I did notice that shortly after adding the RAM the guest demand shot up close to provisioned RAM amount and then dropped to the low demand we have seeing. At that time no one was using the system. What explains this behaviour? I assume it is vsphere doing something internally because of new configuration?

Cheers

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admin
Immortal
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Guest demand is calculated using Active memory. Thus as boot time the OS will "touch" all the memory blocks and thus showing high demand on memory. But like you have seen as soon as things settle after the boot it is back to "normal' again.

Would be interesting to know what the memmory demand was before and now after the VM mem upgrade ?

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AllBlack
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Expert

Thought it was something like that Smiley Happy

I will be monitoring it over next few days and get back to you. The demand has been very constant over last 3 months. There are one or two spikes but that will most likely be related to a reboot then.

Cheers

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