Contributor
Contributor

Hybrid vSAN Configuration

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Hi Everyone,

I'm having some troubles sizing the cache tier for a vSAN Stretched Cluster.

So basically I should use a 1:10 flash to disk ratio, but doesn't vSAN only use up too 600 GB on a single Flash Device?

When I use 800 GB SSDs as a cache tier, does vSAN use the whole 800 GB oder does it only use 600 GB?

Or maybe I'm confusing it with the write buffer of All-flash vSAN.

Hope somebody can answer my question.

I'd like to have multiple disk groups and therefore multiple SSDs, but having the limit of 600 GB somewhat limits my configuration options.

Thanks a lot everyone

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Leadership
Leadership

for hybrid you will do 10% cache to capacity ratio, you don't need to take anything else into account, so don't worry about the 70/30 split, that has been included in our 10% recommendation.

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Leadership
Leadership

In hybrid 30% is used for the write buffer, the rest is read cache. So even with a flash device larger than 600GB all capacity will be used.

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Contributor
Contributor

Thanks a lot.

In that case I've got another question.

If I use a 800 GB SSD, which uses 30% for read buffer, what does that mean for my "flash to disk ratio"?

Do I calculate with the remaining 70% or do I calculate the full 800 GB for my 10% ratio?

E.g. I have 8TB of Capacity. (no overhead or anything calculated for easy of use)

Do I need 1x 800 GB SSD or do I calculate with the remaining 560 GB (70% of 800 GB)?

From my point of view and what I understood from the sizing guide, I'd calculate with 800 GB.

Anyway thanks again for your help and I hope you can also answer my second question.

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Leadership
Leadership

for hybrid you will do 10% cache to capacity ratio, you don't need to take anything else into account, so don't worry about the 70/30 split, that has been included in our 10% recommendation.

View solution in original post

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Leadership
Leadership

I would also highly recommend looking at the ready node configurations, those are usually spot on!

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Contributor
Contributor

Hi Duncan,

thanks again.

So I looked at the ready node configurations and took the used IO controllers and stuff, but I needed a disk set with a quite specific amount of capacity.

Otherwise the ready nodes are good.

For everyone else reading this discussion I marked the answer above as "correct" because it answered my follow-up question regarding the 70/30 ratio.

So my design is complete now and this discussion can be closed.

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