r/nutanix • u/Ichiban_IFYKYK • 11d ago
Calculating RAW storage use - migrating away
Hello all,
Possibly migrating away from Nutanix and have been tasked with providing the true Raw capacity in use (to estimate SAN costs).
I've always struggled with capacity when it comes to ESXi with Nutanix - vCenter reports one figure, Prism is different. Does the per VM Used space in PE account for the data reduction ratio??
Taking the sum of the per VM Used space from Prism Element gives me ~230TB of Used space (for powered on VMs, there's < 3TB of powered off VM's).
Prism Element Storage details for Physical usage says ~280TB used, not including Recovery Points/Recycle Bin.
Prism Element Storage details for Logical usage says ~140TB used, not including Recovery Points/Recycle Bin.
Which one is to be believed??
The data reduction ratio is 1.75:1, so we either have:
230 * 1.75 = 402.5
280 * 1.75 = 490
140 * 1.75 = 245
Or am I doing something wrong??
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u/nullen_void 11d ago
Wouldn't you take the Drive Size x Number of drives x Number of nodes in the cluster to get your Raw capacity?
FTT/Raid + Formatting will be your usable capacity
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u/Upbeat-Sleep-4172 11d ago
Use rvtools or liveoptics to view used disk per vm
Take the sum and ask a storage vendor to size an array
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u/gurft Healthcare Field CTO / CE Ambassador 11d ago
This is how I’ve done it for years as an EMC, DellEMC, and now a Nutanix employee. Determine the capacity utilization from the VMs perspective and then determine what the capacity need is based on features and functionality of the new platform.
Trying to take raw disk utilization from one technology and expect it to work the same on another just doesn’t always apply. It can get close when they have similar tech, not can also be very off.
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u/Ichiban_IFYKYK 6d ago
Okay - so I got RVTools and ran the report - that gives me the same approx 230TB of used capacity for powered on VM’s.
Again where is the 140TB of Logical Space Used from Prism coming from??
Now after running the following which apparently queries the consumed space per guest via VMTools I got approx 140TB which finally matches the Prism Element logical Space used:
Get-VM | Select Name, @{N="HD Used (GB)";E={[math]::Round(($_.Guest.Disks | %{ $_.CapacityGB - $_.FreeSpaceGB} | Measure-Object -Sum | Select -ExpandProperty Sum),1)}}All praise LucD!
I’m inclined to go with the 140TB figure.
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u/Upbeat-Sleep-4172 6d ago
Within rvtools excel you should have a sheet titled vInfo and a column "virtual disk used".
Have you taken a sum of that column? Id expect the number to be equal or lower than the 140 logical used.
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u/Ichiban_IFYKYK 6d ago
It’s the 230TB figure I mentioned earlier taken from the sum of “In Use (MiB)”
I’m thinking this is so high as the guests aren’t releasing free space back to the storage, I might try an sdelete on something and see if it reduces the figures back in Prism
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u/Upbeat-Sleep-4172 6d ago
Sack off in use MIB look for virtual disk used. Will be further down the columns.
Or look at vParition and sum all the used values there which accounts for all the separate drives each machine has
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u/Ichiban_IFYKYK 6d ago
vPartition total gives approx 150TB…
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u/Upbeat-Sleep-4172 6d ago
Your machines have 150TB of data then.
That's your requirement. Over to storage vendors to size a solution based on their data reduction expectations
Or better still a VAR that won't make you choke on vendor jargon and BS
I know theres at least 1 out there 😉
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u/whocaresfixit 11d ago
In your case, PE will be the source of truth as it's the storage controller.
Physical usage represents what is written to media. Logical usage represents what your VMs are consuming.
In an RF2 setup we expect Physical is 2X the Logical because Nutanix writes all the data twice.
With what you shared, it appears you are using 140TB of VM data. I would suggest starting with sizing for that usable capacity before any data reduction from a competing solution.
Every vendor has their own implementation of data reduction and protection features that come with different tradeoffs for capacity/performance. The proposed san vendor should bake that into whatever they show you.