Do you have to use a cache tier with vSAN?

[SRussell]

I am looking at Project NanoEDGE and the layout seems wonky. They are using SuperMicro E300-9D-8CN8TP with dual NVMe m.2 drives. Why would you use a flash tier to cache a capacity tier that is capable of the same r/w profile as the flash tier?

reference: https://www.vmware.com/content/dam/.../products/vsan/vmw-nanoedge-sddc-solution.pdf

 

[markpower28]

Good question, that's the current architecture.

 

[SRussell]

Good question, that's the current architecture.

Does that mean you just have to build it that way?

 

[markpower28]

Correct, that's the current requirement.

 

[Evan]

Bit silly right but yes that’s the way it is.
Remember was developed before NVMe disks were available.

 

[SRussell]

Bit silly right but yes that’s the way it is.
Remember was developed before NVMe disks were available.

Appreciate any feedback. I am trying to keep my lab costs as low as possible. I am looking for anywhere I can lessen the number of parts without impacting performance too much.

 

[Evan]

Can reduce the size of the disk. Smaller size usually = less performance though.
It’s a pretty good minimal config for a modern cluster.
Using older SAS SSD in a bigger chassis for vSAN can make cheaper options I am sure but the appeal of that config is size, power consumption, performance and reasonable cost.

 

[Evan]

Maybe you can partition NVMe to put the cache and data on the same device ? I read somebody else has done that.

 

[Rand__]

Maybe you can partition NVMe to put the cache and data on the same device ? I read somebody else has done that.

I don't think that will work as vSan wants to use the whole disk - it won't accept pre-partitioned disks.

Also bear in mind that with an All Flash setup your cache drive will decide your write performance while the capacity drive will decide your read performance.

 

[Evan]

I don't think that will work as vSan wants to use the whole disk - it won't accept pre-partitioned disks.

Also bear in mind that with an All Flash setup your cache drive will decide your write performance while the capacity drive will decide your read performance.

sorry I should have said namespace rather than partition. NVMe namespaces ‘should’ appear as separate disks to vSAN
Intel SSD as I know don’t support multi-namespace but some others like HGST do...

 

[Rand__]

That might work if you can set these up at device or bios level - but thats going to need hardware thats capable of it which might defeat the idea of cheap (no idea which would, couldnt find much on a quick search)

 

[Spartacus]

Maybe you can partition NVMe to put the cache and data on the same device ? I read somebody else has done that.

vSAN is a software raid solution, it works the similar to FreeNAS, unRAID or the like with JBOD.
I don't believe you can split a drive for SSD and Data, if you could make it work, it would wreck any standardization hope of support/troubleshooting, not recommended.

You can however use a configuration edit to 'mark' drives as SSD to trick it into thinking it has them.

 

[CaptainPoundSand]

sorry I should have said namespace rather than partition. NVMe namespaces ‘should’ appear as separate disks to vSAN
Intel SSD as I know don’t support multi-namespace but some others like HGST do...

NVME disks are hit/miss for namespace support. (M.2 do not, some newer intel do)

I'm currently have 3x ESXI hosts with 1x NVME 1725b spit into 5 name spaces each, so I have 1x 600gb Cache, and 4x 590GB capacity drives. VSAN see's it fairly easily.


VMware vSAN + NVMe namespace magic: Split 1 SSD into 24 devices for great storage performance

 

[Rand__]

Nice!