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R WFlag for United States of America

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Disk Latency with VMware

I am just setting up a VM (windows 7 to be exact) and I notice its taking a long time, going on two hours right now expanding at 30%. It should be done in less than 20-30 mins it shouldn't take this long. This particular VM is assigned 4 procs, 4 gigs of ram  directly connected to a Dell MD3220. There is six other virtual machines running on this host (PowerEdge 510 64 gigs of ram) When I look at the performance tab>Disk the latency seems high. See attached screenshot. We also use Unitrends that replicates other Virtual Machines from another ESXI host at another office to this machine local storage but there are no active jobs that I can see, these typically run at night. What can I do to troubleshoot this?
Avatar of Andrew Hancock (VMware vExpert PRO / EE Fellow/British Beekeeper)
Andrew Hancock (VMware vExpert PRO / EE Fellow/British Beekeeper)
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4 vCPUs is a little over kill for a workstation, I would suggest 1 vCPU or 2 vCPU at maximum, not necessarily if you add more, you could make performance worse.

We allocate between 4 and 16GB RAM to Windows 7 VDI workstations, but this very much depends on how many applications, will be running concurrently.

How is the MD3220 configured, what disks, what RAID ?

is this iSCSI ?

Where is the ISO located ? on a datastore ?

or across the network ? e.g. on your client.

see this about CPUs for reading...

vSMP (virtual SMP) can affect virtual machine performance, when adding too many vCPUs to virtual machines that cannot use the vCPUs effectly, e.g. Servers than can use vSMP correctly :- SQL Server, Exchange Server.

This is true, many VMware Administrators, think adding lots of processors, will increase performance - wrong! (and because they can, they just go silly!). Sometimes there is confusion between cores and processors. But what we are adding is additional processors in the virtual machine.

So 4 vCPU, to the VM is a 4 Way SMP (Quad Processor Server), if you have Enterprise Plus license you can add 8, (and only if you have the correct OS License will the OS recognise them all).

If applications, can take advantage e.g. Exchange, SQL, adding additional processors, can/may increase performance.

So usual rule of thumb is try 1 vCPU, then try 2 vCPU, knock back to 1 vCPU if performance is affected. and only use vSMP if the VM can take advantage.

Example, VM with 4 vCPUs allocated!

My simple laymans explaination of the "scheduler!"

As you have assigned 4 vCPUs, to this VM, the VMware scheulder, has to wait until 4 cores are free and available, to do this, it has to pause the first cores, until the 4th is available, during this timeframe, the paused cores are not available for processes, this is my simplistic view, but bottom line is adding more vCPUs to a VM, may not give you the performance benefits you think, unless the VM, it's applications are optimised for additional vCPUs.

See here
http://www.vmware.com/resources/techresources/10131

see here
http://www.gabesvirtualworld.com/how-too-many-vcpus-can-negatively-affect-your-performance/

http://www.zdnet.com/virtual-cpus-the-overprovisioning-penalty-of-vcpu-to-pcpu-ratios-4010025185/

also there is a document here about the CPU scheduler

www.vmware.com/files/pdf/perf-vsphere-cpu_scheduler.pdf

https://blogs.vmware.com/vsphere/2013/10/does-corespersocket-affect-performance.html
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ASKER

24 disks, 2 on standby. Raid 5 groups> 2. Virtual Disks >2. 16 Terabyte split in half basically.  It is directly attached to the esxi host via SAS cable.
How are you installing ?

any other issues with installations ?
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ASKER

Via WDS/PXE boot. Transfer of the WIM file from WDS seemed to be just fine, right now it is doing expanding. Just says Expanding Windows Files and the percent is going up but very slowly. No other issues that I have been made aware of yet.
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ASKER

I have two other ESXi hosts that I can try with..
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ASKER

I can, I will reset, and start another deployment with one proc. brb
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ASKER

Power On virtual machine 4/10/2015 2:48:54 PM, expanding windows files 1%, current time 3:01pm

1 CPU assigned, 2 gigs of ram
A quick test, to rule out WDS/PXE BOOT, quickly try and ISO.

This will certainly highlight if it's disk I/O or network.
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ASKER

Guess its WDS, were trucking along really fast as it should be. So my WDS server is having issues?
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Avatar of Andrew Hancock (VMware vExpert PRO / EE Fellow/British Beekeeper)
Andrew Hancock (VMware vExpert PRO / EE Fellow/British Beekeeper)
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ASKER

I need to open another question for that I suppose thanks for your help