(nested) VSAN memory requirements


I’m writing this post as there maybe more people like me that don’t read the manual and requirements prior facing errors…

The problems described in this post won’t probably happen with real servers, as they have enough memory. But with lab environments, which always doesn’t have enough memory, you try to give your VMs the least amount of memory possible.

I won’t cover how to setup a nested VSAN environment. William did a great job doing so:
How to quickly setup and test VMware VSAN (Virtual SAN) using Nested ESXi

 

Problem 1: VSAN service not enabled

You either haven’t read the VSAN requirements or haven’t taken them seriously when you encounter following error: 
“Host is in a VSAN enabled cluster but does not have VSAN service enabled”

If you encounter this error you most likely have assigned your (nested) esxi host only 4GB of memory. Once again William blogged already about this:
Re: Host is in a VSAN enabled cluster but does not have VSAN service enabled
And the easy solution is to increase the memory to 5GB.

Ok now you (and I was too) are a little bit smarter and increased the memory to 5GB, added one SSD and one disk and everything was working. Great!
Next thing to test: adding a second disk.

 

Problem 2: Cannot add 1 disks to SSD

Whoops:

vsan_error

“A general system error occured: Cannot add 1 disks to SSD. Currently mapped 1 disks, maximum 1 disks.”

Why am I receiving this error? Actually VSAN is quite picky regarding the memory configuration!
I’ve read again the VSAN requirements and noticed that the minimum memory requirements are not 5GB but 6GB! (William posted 5GB and I’m quite sure that the KB was also writing 5GB in an earlier version)

Again I increased the memory, now to 6GB, tried to add a disk and it worked!

Finally I did some more search and found a blog post from Cormac Hogan:
VSAN Part 14 – Host Memory Requirements
There you can find a table with the memory recommendation for VSAN:

Memory Amount (GB)
Max Number of Disks
Max Number of Disk Groups
Max Number of Disks per Disk Group
6
2
2
2
8
5
5
5
12
10
5
7
16
15
5
7
20
20
5
7
24
25
5
7
28
30
5
7
32
35
5
7

These are no recommendation, these are minimum requirements!

To doublecheck I added a third disk to my esxi with 6GB memory and again received a similar error but now stating that I only can have 2 disks:
“A general system error occured: Cannot add 1 disks to SSD. Currently mapped 2 disks, maximum 2 disks.”


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