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FunkyD
Contributor
Contributor
‎12-11-2007 07:20 AM

Can I reduce client memory? - never goes above 25%

I have a SQL 2005 server that has 3GB of memory but the memory usage (as seen in VC) has not gone above 25% for the last year. Does that imply that I can reduce the amount of memory on the server to say 2GB - or even 1.5GB and it continue to run ok? I know I can test it and see but I am more itnerested to know if I am making the right conclusion.

Thanks

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vmroyale
Immortal
Immortal
‎12-11-2007 07:26 AM

I think that is a correct conclusion. Drop it to 2Gb and continue to monitor. Couldn't hurt!

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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MR-T
Immortal
Immortal
‎12-11-2007 07:47 AM

Go for it. I think you'll find it works just the same.

This is a fantastic opportunity to demponstrate how flexible a vm can be.

Being able to decrease the servers memory without physically opening boxes is great.

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esiebert7625
Immortal
Immortal
‎12-11-2007 08:26 AM

With VM's as a general best practice you should never give them more memory then they need. Start with a minimal amount of memory and only increase it if it will benefit the VM. On a SQL Server it will depend on your SQL memory settings. If you have it set to dynamically allocate memory then it will use all the memory it can from the host system. If you set it to a fixed amount then it will never use more then that amount. It's best to do an analysis of your SQL server and see what the optimal memory it needs for the databases it supports. Usually a SQL admin will be able to determine this. In your case I would reduce the amount of memory if it is not being used.

Eric Siebert

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RParker
Immortal
Immortal
‎12-11-2007 08:56 AM

VC reports HOST memory usage, not ACTUAL memory usage of the guest. You should use the SQL task manager to monitor the ACTUAL usage inside the VM. Taking 1 Gig away or 1.5Gig away from SQL may be a HUGE hit, due to the way SQL manages it's cache.

Some guests only need 700 Meg of HOST memory to give the Guest 3G of memory, if you reduce the memory for the guest by half, you are only hurting the VM itself, not the host, since the gain is minimal on the host.

I would monitor the memory inside the VM first, before you start assuming you can reduce the memory with no impact. And don't take giant chunks of memory away from SQL, take a little at a time and monitor performance, I wouldn't reduce it by more than 2.5G until you are SURE it's working like before...

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FunkyD
Contributor
Contributor
‎12-12-2007 08:06 AM 

Some guests only need 700 Meg of HOST memory to give the Guest 3G of memory, if you reduce the memory for the guest by half, you are only hurting the VM itself, not the host, since the gain is minimal on the host.
Believe it or not but I never knew this. I have read the documentation so I guess I just didn't interpret it correctly. I have always given guests the same memory that they had as physical machines - e.g. if an app says it needs a server with 2GB of memory then I've built a Vserver with 2GB of memory.
I have quite a few servers that have 1GB of memory but only seem to show around 10-20% guest usage. I guess all of these are potential targets to claw back some memory for new hosts?

					
				
			
			
				
			
			
			
			
			
			
			
		

		
		
	

	
	


	
				
		
			
		
			
		
			
					
			
		
				
		
			
					
		
	
				
		
			
					
		
	
				
		
			
					
		
	
				
		
			
					
		
	
				
		
			
					
		
	
				
		
	
	


		

	

		

			

	
		
			
					
				
		
			
		
			
					
		
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Here's some good reads if you want to know more about memory manegement in ESX...
 
Host Mem and Guest Mem % - http://www.vmware.com/community/thread.jspa?messageID=620581  
Memory Resource Management in VMWare ESX Server - http://www.stanford.edu/~stinson/cs240/cs240_1/revs/esx.txt
The Role of Memory in ESX Server 3 - http://www.vmware.com/pdf/esx3_memory.pdf
Memory resource management in Vmware ESX Server - http://www.vmware.com/pdf/usenix_resource_mgmt.pdf
Understanding memory usage in Windows 2000 - http://www.microsoft.com/technet/prodtechnol/windows2000serv/tips/w2mem.mspx
Memory performance - http://www.vmware.com/community/thread.jspa?threadID=65293
Memory Shares/Limits/Reservations - http://www.vmware.com/community/thread.jspa?threadID=73411
RAM, Virtual Memory, Pagefile and all that stuff - http://support.microsoft.com/?kbid=555223
Understanding the Impact of RAM on Overall System Performance - http://www.windowsnetworking.com/articles_tutorials/Understanding-Impact-RAM-Overall-System-Performa...
RAM, Virtual Memory, Pagefile and all that stuff - http://members.shaw.ca/bsanders/WindowsGeneralWeb/RAMVirtualMemoryPageFileEtc.htm
Eric Siebert
VMware Communities User Moderator
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