This task explains how to calculate the capacity of a VSA cluster that uses hardware RAID5 or RAID6 configuration.

In this configuration, the capacity of the VSA cluster depends on the following variables:

Number of hard disks in the hardware RAID set. The number of disks you can have in the RAID5 configuration is 4 to 8. In RAID6, the number of disks is 5 to 8. VMware recommends that you use RAID5 for SAS drives and RAID6 for SATA drives.

Capacity of a hard disk in the hardware RAID set. For simplicity, assume that all hard disks are of equal capacity.

Number of ESXi hosts in the VSA cluster (2 or 3).

1

Calculate the storage capacity available on each ESXi host. The formula you use depends on your RAID configuration.

For RAID5, use the following formula. The number of disks you can have in the RAID5 configuration is 4 to 8.

total storage capacity per host = (number of hard disks in the RAID - 1) times hard disk capacity

For RAID6, use the following formula. The number of disks you can have in the RAID6 configuration is 5 to 8.

total storage capacity per host = (number of hard disks in the RAID - 2) times hard disk capacity
Note

If your hosts have different total storage capacities, the lowest value among all VSA cluster hosts becomes the basis for calculating the capacity of every VSA datastore. Some of the total storage capacity remains unused in this case.

2

Calculate the capacity of a RAID5 or RAID6 VSA datastore by using the following formula:

capacity of a VSA datastore = total storage capacity per host divided by 2

The value that you get is a combination of the storage efficiency of the hardware RAID5 or RAID6 configuration on each of the ESXi hosts and the mirroring of VSA volumes between VSA cluster members.

3

Calculate total capacity of a VSA cluster by using the following formula:

total VSA cluster capacity = capacity of a VSA datastore times number of hosts in the VSA cluster

For the RAID5 example, the following parameters are used:

Number of hard disks in the hardware RAID5 set: 8

Capacity of each hard disk: 500GB

Number of ESXi hosts in the VSA cluster: 3

total storage capacity per host = (8-1) * 500GB = 3.5TB
capacity of a VSA datastore = 3.5TB/2 = 1.75TB
total VSA cluster capacity = 1.75TB * 3 hosts = 5.25TB

For the RAID6 example, the following parameters are used:

Number of hard disks in the hardware RAID5 set: 8

Capacity of each hard disk: 1TB

Number of ESXi hosts in the VSA cluster: 3

total storage capacity per host = (8-2) * 1TB = 6TB
capacity of a VSA datastore = 6TB/2 = 3TB
total VSA cluster capacity = 3TB * 3 hosts = 9TB