Heterogenous Datastore

Hybrid Datastore (Three Hosts and Above)

Requirements

Condition 1: The sum of the data disk capacity between hosts, the highest capacity, cannot exceed 80% of the sum of all the remaining hosts. Example: host A 5TB, host B 5TB, host C 5TB, host D is not allowed to exceed 12TB.

Condition 2: The ratio of the cache disk capacity to the data disk capacity of each host should not be less than 5%. For example, host A configuration with two 480GB SSDs and ten 4TB HDDs is not allowed.

Condition 3: The ratio of each host’s cache disks and data disks should be within 1:6. For example, host A has two cache disks and fifteen data disks, which is not allowed.

Condition 4: It is allowed to have a data disk with different capacities in a single host, but the capacity gap of the largest data disk should not exceed two times of the smallest data disk. For example, a 1TB disk and a 4TB disk can form virtual storage but do not form a 1TB disk and a 4TB disk in the same disk group. The capacity of a 4TB disk is four times larger than a 1TB disk, but the performance is the same as a 1TB disk, so a 4TB disk can easily become a performance bottleneck. The bigger the gap, the bigger the bottleneck.

Precautions

1. The HDD in the host allows SAS disks and SATA disks to be mixed, but it will cause the performance of SAS disks to be equal to SATA disks (barrel effect).

2. The host is allowed to have a varying number of disks between disk groups. The main impact is that the write performance will drop slightly when the storage pool is almost full.

All-Flash Datastore (Three Hosts and Above)

The following requirements are for hosts within a single storage datastore. There is no heterogeneity requirement between multiple datastores.

Condition 1: The sum of the data disk capacity between hosts, the highest capacity, cannot exceed 80% of the sum of all the remaining hosts. Example: host A 5TB, host B 5TB, host C 5TB, host D is not allowed to exceed 12TB.

Precautions

1. For all-flash datastores, configuring cache disks is not required. However, it is recommended to configure all SSDs as data disks.

2. It is allowed to have a data disk with different capacities in a single host, which will not affect the performance.

Two Hosts Scenario

Heterogenous Requirements

Condition 1: The total capacity of the two hosts must be equal.

Condition 2: The ratio of the cache disk capacity to the data disk capacity of each host should not be less than 5%. For example, host A configuration with two 480GB SSDs and ten 4TB HDDs is not allowed.

Condition 3: The ratio of the number of cache disks to data disks of each host should exceed or equal to 1:6. For example, host A has two cache disks, and fifteen data disks are not allowed.

Condition 4: It is allowed to have a data disk with different capacities in a single host, but the largest data disk capacity is not allowed to exceed two times the capacity of the smallest data disk. For example, a 1TB disk and a 4TB disk can form a virtual storage datastore but do not form a 1TB disk and a 4TB disk in the same disk group. The capacity of a 4TB disk is four times larger than a 1TB disk, but the performance is the same as a 1TB disk, so a 4TB disk can easily become a performance bottleneck. The bigger the gap, the bigger the bottleneck.

Precautions

When expanding the capacity of two hosts in a datastore, the entire HCI cluster needs to be restarted.

Precautions for Multi-Datastore Expansion

1. A cluster can have up to six virtual storages.
2. Two hosts’ environment does not support expanding the second virtual storage.
3. When having multiple virtual storage datastore, each datastore requires at least three hosts.
4. The disk-based datastore only allows two ordinary datastore to be created on one host.
5. Versions earlier than HCI 6.2.0 do not support disk-based datastore. Only one virtual datastore can be created on a host.
6. The stretched cluster does not support creating a second virtual storage. A host also cannot have both stretched and ordinary datastore.
7. The hosts spanning a datastore cannot belong to the other two storage datastores.