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ssd to hdd ratio recommendation for VSAN deployment

Ben Conner
Ben Conner asked
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Hi,

I'm considering converting to a VSAN architecture with a hybrid model and am curious if there is any recommended ssd vs hdd ratio that is recommended?  One host I already have a 500GB ssd in, but will need to buy one for the 2nd one.

Right now, I have 4.8TB of hdd space on the host that has the 500TB ssd drive, and 7.8TB of hdd space on the host that has no ssd on it.

Not all of this space is active VMs, and of those that are, 90% of the time they are lightly loaded.

--Ben
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Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017
Commented:

If you are considering Hybrid, it's one SSD device per Disk group of HDD.


e.g. once caching tier per HDD per disk group.


and then you can build one or more disk groups per host, either SSDs and HDDs.


Unless you do all flash.


Tread very carefully with vSAN, that you purchase a vSAN Ready Node, or MAKE absolutely certain ALL hardware and firmware are on the HCL.


It's not just a case of bung in SSD and HDD, 10GBe networking, and off we go into production.


If Lab okay experiment.

Ben ConnerCTO, SAS developer

Author

Commented:
Thanks, Andrew.  Is there a minimum size ssd or a ssd to hdd ratio(e.g., 1tb SSD to 5TB hdd) I should be a ware of, or is that not as important?

--Ben
VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017
Commented:

The flash caching device must provide at least 10 percent of the anticipated storage that virtual machines are expected to consume, not including replicas such as mirrors.


Source

https://docs.vmware.com/en/VMware-vSphere/6.5/com.vmware.vsphere.virtualsan.doc/GUID-1D6AD25A-459A-43D6-8FF5-52475499D6A2.html

Ben ConnerCTO, SAS developer

Author

Commented:
Perfect.  Thank you sir.
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017

Commented:

no problems.