Difference between single site cluster and single site cluster with custom fault domain

[baber]

When we want enable vSAN , there are two options :

1- Single site cluster

2- Single site cluster with custom fault domain .

Imagine I have 5 esxi hosts in my cluster by default each host is a fault domain in single site cluster I can use FTT=1 raid5

1- but if I create fault domain have to create 3 FD ( 2 fault domain with 2 hosts and 1 fault domain with one host) so in this type I cannot use FTT=1 raid5 .   Is that correct ?

2- If I want use FTT=1 raid5 had to exist 5 fault domain so we have to had about 10 esxi host in the cluster (5 fault domain with 2 hosts). Is that correct ?

[TheBobkin]

@baber If this is a single-site cluster with all servers in one rack then just use 'Single site cluster'.

"Imagine I have 5 esxi hosts in my cluster by default each host is a fault domain in single site cluster I can use FTT=1 raid5"
FTT=1,FTM=RAID5 requires 4 nodes/Fault Domains(FDs) for component placement and when not defined by FD configuration each node is a FD so yes.

"1- but if I create fault domain have to create 3 FD ( 2 fault domain with 2 hosts and 1 fault domain with one host) so in this type I cannot use FTT=1 raid5 . Is that correct ?"
Correct. No as it has 3 FDs and 4 are required.

"2- If I want use FTT=1 raid5 had to exist 5 fault domain so we have to had about 10 esxi host in the cluster (5 fault domain with 2 hosts). Is that correct ?"
You would need 4 FDs, if wanted to go N+1 then 5 FDs, this would only be of any possible benefit if each 2 servers were in 5 different racks or something like that.

[baber]

Thanks. I have 5 esxi hosts and resided on 2 Racks (2 hosts in one rack and 3 hosts in the other rack) I want use FTT=1 with raid5 . Is that possible machine' disk reside on hosts in rack1 and replica disk reside on hosts in rack2?

[TheBobkin]

No because that is not how RAID5 works - it doesn't store data as 2 replicas like RAID1 does, it provides redundancy via all data-components containing a mix of data and parity data that could be used to rebuild the data in the event of a failure, storing the data in this manner requires a minimum of 4 nodes/FDs.

[baber]

Imagine I am using FTT=1 raid 1 and I have 3 esxi hosts (2esxi hosts placed in rac1 and one esxi host reside in rac2) I want when create vm with FTT=1 replica disk place on the other rac actually I just want replica disk or replica components reside on the other host in rac2 while each host is one FD