msemon1
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Expert

Additional SCSI controller

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Is there a performance benefit from adding an additional SCSI controller? I have a VM with 2 virtual disks and 3 RDM's. I am thinking about adding a second SCSI controller for the RDM's.

Mike

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andosm
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Enthusiast

The answer is: it depends Smiley Happy

If you have vSphere and switch to PVSCSI adapter you can have up to 12% throughput and up to 18% less cpu utilization. More info here. There are also some drawbacks here.

There's also good KB Article.

If you don't have vSphere the only difference between one and two SCSI controllers will be possibility to separate "SCSI Bus Sharing settings" between disks.

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Pozdrawiam/Best Regards

Andrzej

Pozdrawiam/Best Regards Andrzej

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andosm
Enthusiast
Enthusiast

The answer is: it depends Smiley Happy

If you have vSphere and switch to PVSCSI adapter you can have up to 12% throughput and up to 18% less cpu utilization. More info here. There are also some drawbacks here.

There's also good KB Article.

If you don't have vSphere the only difference between one and two SCSI controllers will be possibility to separate "SCSI Bus Sharing settings" between disks.

--

Pozdrawiam/Best Regards

Andrzej

Pozdrawiam/Best Regards Andrzej
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msemon1
Expert
Expert

That's interesting. So PVSCSI and VMXNET3 cannot be used on FT VM's. Also, if PVSCSI cannot be used on boot disks than that is another drawback. We are on Vi 3.5. Is it worth adding another SCSI controller to separate the SCSI bus sharing setting between disks?

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andosm
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Enthusiast

only if you have plans to use clustering (for example MSCS) on VM's level.

for example to share data disk between VM1 and VM2 you will need:

VM1 - SCSI contro 1 - boot disk - sharing NONE, SCSI contro 2 - data disk - sharing YES (physical or virtual)

VM2 - SCSI contro 1 - boot disk - sharing NONE, SCSI contro 2 - data disk - sharing YES (physical or virtual)

You can set SCSI bus sharing in VM Settings -> SCSI controller settings

If you have plans to use more than 16 virtual disks for one VM you will also have to have second SCSI contro Smiley Happy

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Pozdrawiam/Best Regards

Andrzej

Pozdrawiam/Best Regards Andrzej