vSAN sizing calculator - why so much overhead

[jooji_marsh]

Hi,

Im struggling to find justification in the vSAN sizing calculators vs real life. I've configured a couple of hybrid and all-flash clusters over the last few years and im currently speccing a 76TB all flash cluster. the vSAN calculator is telling me i need 5 nodes with 12 x 3.84TB capacity disks giving 225 raw and 92 useable. Thats a lot of overhead?

Looking at another 45TB cluster i deployed last year i have 5 nodes with 8 x 1.2TB capacity disk per node giving me 43TB raw and basically the same useable. The overhead is only about 700GB.

So whats the crack?

[TheBobkin]

Hello jooji_marsh​

Assuming FTT=1,RAID=1 Storage Policy and the VMware recommended ~25% slack space, 92TB usable = 230TB raw, thus I don't see what the issue with this is.

"Looking at another 45TB cluster i deployed last year i have 5 nodes with 8 x 1.2TB capacity disk per node giving me 43TB raw and basically the same useable. The overhead is only about 700GB."

43TB raw and "basically the same useable" implies everything here is FTT=0 and you are not caring for slack space recommendations (both of which choices are by all means your own choices).

"So whats the crack?"

Sorry, pedantic Irish person here - the phrase is "What's the Craic" assuming you meant 'what is up with this' :smileygrin:

Bob

[jooji_marsh]

No yes i think penny has dropped. I was expecting useable to be the actual figure you see in vSphere but you actually see 230TB but taking into consideration what you actually need + overheads + FTT RAID etc.

Yes i meant craic haha

Thanks

[ZibiM]

Hello

My favourite VSAN calculator is:

vSAN-usage

It really shows in easy way the impact of different approaches to VSAN cluster design and what really eats this space

Hope it helps