minimum hosts/Fault Domains for FTT=2

[vmb01]

I'm trying to figure out the minimum number of hosts (fault domains) required for an FTT=2 policy.

I believe that if we use RAID 6 in OSA, it creates a 4+2 setup. As a result, the minimum number of hosts/fault domains needed is 6.

However, I don't understand why the admin guide states:
"For n failures tolerated, each piece of data written is stored in n+1 places, including parity copies if using RAID-5 or RAID-6."

Could someone help me understand this, please?

[Geogee]

Hello,

the exact formula is 2n+1 for RAID1 - mirroring. - 2,3,4 mirrors and some witness components to have odd number of components.

For Erasure coding (RAID5/RAID6) it is  2n+2

Fx.

RAID 1 - FTT 2 = 2*2+1 = 5 hosts minimum

RAID 6 - FTT 2 = 2*2+2 = 6 hosts minimum

------------------------------
Jiri Viktorin
VCIX-DCV, VCIX-NV, VCF-VCI, vExpert
------------------------------

[Pawel Koc]

[vmb01]

Great Table Pawel,

Please, where can customer find a VMware documentation about it?

Thanks in advance

Bye

[Pawel Koc]

Description of vSAN Policies:

https://docs.vmware.com/en/VMware-vSphere/8.0/vsan-administration/GUID-C8E919D0-9D80-4AE1-826B-D180632775F3.html

RAID Space Requirements:
https://docs.vmware.com/en/VMware-vSphere/8.0/vsan-administration/GUID-AD408FA8-5898-4541-9F82-FE72E6CD6227.html 

[vmb01]

Thank you, Pavel.

The first link you mentioned is the same one I referred to at the beginning of this thread. It includes the formula for calculating Fault Domains in a RAID1 configuration but does not cover RAID5/6.