Slow disk performance with vmdk

I have a Dell Server with a H330 Raid card, set up with 4 disks in a RAID 10 of 4 disks.

I have the latest esxi 7 and patch level installed on a usb stick.

I have a 8GB, 8 Core Windows 2019 virtual machine with a seperate vmdk of around 1.8tb for data.

I ahve installed the Dell extensions for esxi with their updated drivers etc.

The issue is that if i run diskmark, i'm getting only around 50-70mbps write speed out of my vmdk.

What i've tried so far.

I've an old server which is being retired (non esxi) It'sserver 2012 essentials installed directly to a raaid 5 array of 4 disks. This server also has a H330 card. Running diskmark on here, i'm getting  an average od 194mbps write and 380mbps read.

I decided to take a copy of the esxi vmdk's and set up virtualbox on the old server. I gave the VM the same, 8GB ram etc and re-ran the diskmark test. I got an average of 88mbps write, 110 read.

Now, I know that with a virtual machine, you'd expect a little loss in speed however this is ridiculous.

Is there something i'm doing wrong? or is this result expected?

I moved the VM to the old machine in VirtualBox with the plan of wiping the array on the new server and replacing it with raid5 however the test above looks as though it won't make any difference?

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2 Replies

Hey, hope you are doing fine:

Please check the following:
Install a new virtual machine on ESXi with any other operating system than Windows 10 1908 and Windows 2019 and check how is performance going.

Also, can you tell which virtual hardware have you assigned to the VM?
How many CPU, memory, which controller, etc

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I'm afraid that this is an expected result.

ESXi itself doesn't do any read/write caching, but relies on the RAID controller's cache. Since the H330 works in write-through mode (no cache), each singe write operation has to be acknowledged by the disks, which makes it so slow. For ESXi - except for vSAN configurations - a RAID controller with battery buffered write-back cache makes a huge difference.


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