Fail-Over with Limited Resources

[TheKid7]

I am new to VMware.  I support a recently commissioned Dell VRTX Server (3 Blades).  Please answer the following questions:

1.  How does Fail-Over work if you have limited resources?  When I set-up the Dell VRTX Server, I got very conservative with RAM allocation to some of the VM's.  Mainly it is one VM that I am concerned about (64 GB RAM).  I have plenty of storage for both the current and future VM's, so I won't mention storage size/allocation in the discussion.  My current setup is:

Blade 1:

VM#1 8 CPU Cores, 64 GB RAM

VM#2 4 CPU Cores, 16 GB RAM

Blade 2:

VM#3 4 CPU Cores, 32 GB RAM

VM#4 4 CPU Cores, 16 GB RAM

Blade 3:

VM#5 8 CPU Cores, 32 GB RAM

Each Blade:  2 CPU's (20 Logical Cores/CPU), 128 GB RAM

Later this year I plan to add at least two (2) more VM's (The RAM allocation may be a little higher than listed.).

VM#6 4 CPU Cores, 16 GB RAM

VM#7 4 CPU Cores, 16 GB RAM

Operating System On All VM's:  Windows Server 2012 R2 64 bit

2.  I am concerned that if Blade 1 fails and later I have a lot more Total VM's, what happens if the RAM allocation of the VM's on the failed Blade exceeds what is available on the Blade(s) to which the VM's fail-over?

I plan to recommend to increase the amount of RAM to 192 GB (minimum) per Blade, just to be safe.  However, there is a chance that the RAM increase may not get approved.

Thanks in Advance.

[illvilja · Accepted solution]

Hi,

If the allocated amount of vRAM exceeds the available pRAM your VMs will have a bad time. Transparent page sharing, compression will help but eventually your VMs will begin to swap and it will be very noticeable.

http://www.vmware.se/pdf/Perf_Best_Practices_vSphere5.5.pdf

Regards,

Martin

[kiraa]

As stated by Illvilja above. If the VM starts using more than the host can provide it will start swapping memory which has a very noticeable performance impact.

I would push this as hard as you can for approval as the performance impact can be dramatic + the more RAM you have will allow you to future proof in case you need to add another VM or two in there.

Thanks,

Jake

[TheKid7]

Thanks everyone.

I will ask for more memory.