Maximum SSD to HDD Ratio

  • 23 August 2016
  • 4 replies
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Badge +7
just wondering the following:Everywhere you look it shows nutanix configuration of 2 or 4 SSD with the rest being HDD. With the advance of having all flash nodes on every model, is there anything stopping us having lets's say 6 SSD and 4 HDD? Or 5 of each in a node supporting 10 Disks?Does the Pro License also enable us to pin VM or part of it to SSD?

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4 replies

Userlevel 1
Badge +4
This is just my .02 but generally speaking, the idea behind hybrid is that your active dataset can fit within the SSD tier with a little bit of head room to spare to be the most cost efficient, and I suppose with the caveat that occasionally you may hit some infrequently used data in the cold tier before/without it getting moved to SSD. Whereas with all flash, you either want/need to guarantee that all IO occurs on SSD and/or have lots of money to spend. My guess would be if you started getting towards the 50/50 SSD/HDD or 60/40 SSD/HDD ratio you're probably getting close to the price of an all flash config anyway so I guess you'd just be getting a little extra overall capacity thanks to the HDD tier.

Will you run out of CPU and memory before disk performance becomes an issue? I always do. If so then perhaps more nodes will be required anyway to support the workload from a CPU & memory perspective and you might not truly need the extra capacity in the HDD tier, or maybe the amount of flash you're targeting.

Interesting idea though.
Badge +7
What about the pin to ssd feature?
Badge +7
Now that all models supports all flash, will there be the pin to ssd available on pro licenses as well or is that still being restricted to ultimate?

Also if you had to choose between this two config what would you choose?

3 x Nodes:
6 x 400GB SSD
4 x 2TB SATA

or

3 x Nodes:
4 x 400GB SSD
6 x 2TB SATA
Userlevel 6
Badge +29
Going to send a note to our Product Management team to triple check, but I'm almost certain "VM Flash Mode" is going to stay an Ultimate feature.

IMHO, while it is neat for things like service provider use cases, I dont see this widely applicable to the enterprise, especially since All Flash is so pervasive now. I'd rather have you go higher on SSD spindle count, rather than HDD spindle count if you are concerned with the amount of "hot data" within a cluster, rather than you trying to partition the existing flash with VM Flash Mode (i.e Pin to SSD).

This of course assumes that you are not capacity contrained, or your capacity is otherwise taken care of through data reduction techniques like in-line compression (which we highly recommend on just about any workload, and it works across SSD and HDD too).

That said, just curious, is there a specific driver for this Pin to SSD question (i.e performance issue, demand from the business, demand from a specific application, etc)?

Jon