What are differences in storage performance between virtual machine and physical one?

[kendzi87]

Has any one met with research regarding comparison in IOPS performance between virtual machine and physical one.
I am interested in information about 3 configurations (assuming OS is storage that is not tested):

1. IO from psychical OS to drive.

2. IO from virtual Os to drive that is part of datastore.

3. IO from virtual Os to drive that is passthrou to virtual machine.

I found information about CPU and memory usage but i didn't find straight answer to my questions

Theoretical answer is also appreciated.

[HassanAlKak88]

Hello,

IOPS (input/output operations per second) is the standard unit of measurement for the maximum number of reads and writes to non-contiguous storage locations.

IOPS is frequently referenced by storage vendors to characterize performance in solid-state drives (SSD), hard disk drives (HDD) and storage area networks.

IOPS numbers are affected by the size of the data block and workload performance, it's unlikely that vendors will use standardized variables when listing IOPS. Even if a standard system were used to determine IOPS, with a set block size and read/write mix, that number means nothing unless it matches up to a specific workload.

As conclusion, it is not related to Physical/Virtual OS.

Please consider marking this answer "CORRECT" or "Helpful" if you think your question have been answered correctly.

Cheers,

VCIX6-NV|VCP-NV|VCP-DC|

@KakHassan

linkedin.com/in/hassanalkak

[kendzi87]

Hi

I know what IOPS are

I just wonder is virtual layer somehow affecting, reducing number of it when comparing performance of virtual platform and psychical one.
I think that there are should be some delay because of Virtual Machine Monitor or VMKernel. I just want to confirm or deny my logic.

[continuum]

To create a VM you need to select one out of  the following options:	Overhead of VMFS-filesystem	IO-Performance benchmarks put your figures here	Overhead for scheduling resources	Overhead for virtual hardware inside VM	Overhead for NTFS filesystem	Reacts to power- failures like a physical ...	Readable when VMFS layer fails
VM uses a thick VMDK stored on VMFS	small	?	small	small	significant	almost as good as Windows	requires precautions
VM uses a thick VMDK stored on VMFS via iSCS	small	?	small	small	significant	almost as good as Windows	requires precautions
VM uses a thin VMDK stored on VMFS	small - very large	?	small	small	significant	ESXi	no
VM uses a thin VMDK stored on VMFS via iSCSI	small - very large	?	small	small	significant	ESXi	no
VM uses a thin VMDK stored on NFS	none	?	small	small	significant	like a NFS-server	yes
VM uses RDM-VMDK	very small	?	small	small	significant	Windows	yes
VM uses a separate SCSI-device in pass through	none	?	small	small	significant	Windows	yes

Folks use IO-benchmarks in the hope that it helps to decide the question:

What VMDK-type should I use in my case ?
Hope my little table helps to put the IO-benchmark-results in to perspective.
I highly recommend to decide this questions with the highest priority given to the column: Reacts to power-failures like a physical ...
IO-benchmarks may be useful - but dont ignore the other factors I listed.
The smaller the environment is the more relevant the other factors are.