When a node is lost in a vSAN cluster, the vSAN will automatically begin to rebuild objects in order to meet the storage policy compliance. However, if the storage policy includes RAID-5 with a "Failures to Tolerate" (FTT) value of 2, it won't be possible to rebuild the objects and meet the storage policy compliance with only 5 nodes. In this case, the vSAN administrator needs to change the RAID-5 FTT from 2 to 1, this will allow the vSAN to rebuild the objects and meet the storage policy compliance with only 5 nodes. With RAID-5, the FTT value of 1 is the minimum value supported by vSAN.

This is explained in VMware vSAN documentation in the section "RAID-5 and RAID-6 Erasure Coding" Reference: https://docs.vmware.com/en/VMware-vSphere/7.0/vsphere-vsan-70-config-guide/GUID-1A5F48D5-F8C9-4C7E-9D9B-F9D4B4E4A4F4.html

Changing the RAID-5 FTT from 2 to 1 will ensure that the virtual machines on the vSAN datastore are in compliance with the storage policy. This is because, with a RAID-5 FTT of 2, the cluster needs at least 6 nodes to meet the redundancy requirements. With a single node lost, the cluster cannot meet this requirement and so the virtual machines on the datastore will be out of compliance. By changing the FTT from 2 to 1, the cluster will be able to meet the redundancy requirements with only the remaining 5 nodes, ensuring compliance with the storage policy. Reference: https://docs.vmware.com/en/VMware-vSphere/7.0/com.vmware.vsphere.troubleshooting.doc/GUID-F7A0FECC-E95E-4A89-B3B3-9699D9F7D87D.html

The RAID configuration that the administrator must use in this storage policy to achieve the best performance for the database virtual machines is RAID-6.

RAID-6 is an effective configuration for a vSAN cluster with eight hosts as it allows for two hosts to fail and still maintain protection of the data. RAID-6 is a data striping configuration with two parity bits stored across multiple disks, which improves read performance while also providing fault tolerance.

For more information, see the official VMware guide on vSAN Storage Policies: https://docs.vmware.com/en/VMware-vSphere/6.7/com.vmware.vsphere.vsan.doc/GUID-DAC07A3E-A077-4A93-A9D0-9CBB2F4F4B4D.html

Each site in the stretched cluster is configured as a fault domain. Fault domains are used to spread redundancy components across servers. In a traditional vSAN cluster, redundant components are spread across servers in separate computing racks, and as a result, can tolerate rack failures, cache and capacity device failures, network device failures, and power failures. When used in a stretched cluster, fault domains spread redundancy components across sites, and therefore can tolerate the failure of an entire data site. The minimum number of hosts in a stretched cluster is three, one host in each data site plus the witness host in the witness site. The maximum number of hosts in a stretched cluster is 31, fifteen hosts in each data site plus the witness host in the witness site.

Site Recovery Manager (SRM) provides disaster recovery orchestration for workloads on a vSAN stretched cluster to a third site. SRM is a disaster recovery solution that automates the recovery and migration of virtual machines between sites. It allows you to protect your applications and data by failing over to a secondary site in case of a disaster or planned maintenance. SRM also enables testing of recovery procedures without impacting production workloads.

The three steps to configure the vSAN Direct Configuration for vSphere with Tanzu are: C. Create a storage policy for vSAN Direct; D. Create a vSAN storage policy with FTT=0; and F. Claim unused disks for vSAN Direct.

According to VMware's documentation, the "No Data Migration" option for maintenance mode should be used when the expected maintenance time is less than one hour. This option will allow the administrator to complete their maintenance without having to wait for a full data migration, which can be time consuming and also has additional capacity and performance considerations. It is important to note that this option will not guarantee the same level of availability as the other options, so it should only be used when the expected maintenance time is less than one hour.

vSAN 2-Node Cluster Guide | VMware

https://core.vmware.com/resource/vsan-2-node-cluster-guide

Deploying a vSAN Witness Appliance

https://docs.vmware.com/en/VMware-vSphere/7.0/com.vmware.vsphere.vsan-planning.doc/GUID-05C1737A-5FBA-4AEE-BDB8-3BF5DE569E0A.html

vSAN Stretched Cluster Guide | VMware

https://core.vmware.com/resource/vsan-stretched-cluster-guide

The TRIM and UNMAP capability of vSAN is used to reclaim space on an all-flash vSAN cluster by discarding blocks that are no longer in use. In order to use this capability, the following prerequisites must be met:

• The VM guest operating system must support the ATA TRIM or SCSI UNMAP command. This will allow the guest OS to communicate with the vSAN datastore to inform it of blocks that are no longer in use.
• The vSAN cluster must be an all-flash architecture. TRIM and UNMAP can only be used on all-flash vSAN clusters, as it doesn't make sense on the hybrid vSAN cluster.

This is explained in VMware vSAN documentation in the section "vSAN Space Reclamation" Reference: https://docs.vmware.com/en/VMware-vSphere/7.0/vsphere-vsan-70-admin-guide/GUID-7E8F6C98-7C0B-4D21-8F1A-F3A3A9F4F4A4.html

The maximum time range that can be stored by the vSAN health check history is 180 days (C). According to the VMware Official Guide, “The vSAN Health Check history is stored for up to 180 days before it is automatically purged.”

The Cache Disk will be marked as failed, and the Ensure Accessibility option will be required before any components are rebuilt. When a single cache disk fails within one of the vSAN hosts, the Disk Group will be marked as failed and the Ensure Accessibility option will be required before any components are rebuilt. The Ensure Accessibility option will rebuild the components on other cache disks, as long as sufficient capacity is available.

Self-Monitoring, Analysis and Reporting Technology (SMART) is an industry-standard technology that allows hard drives to report on their own health, including the ability to predict possible future failures. When configuring the vSAN Adapter Instance in vRealize Operations Manager, the administrator should enable SMART data collection to be able to receive analytical information from the hard drives and monitor their health.

By enabling SMART data collection, the administrator can use the data to identify potential issues with hard drives, monitor their health status, and take appropriate actions to prevent data loss.

This is explained in VMware vSAN documentation in the section "Monitoring vSAN Disk Health with vRealize Operations Manager" Reference: https://docs.vmware.com/en/VMware-vSphere/7.0/vsphere-vsan-70-admin-guide/GUID-9A9B1E1A-7D56-4C0B-A8C2-2A7E27AED9B9.html

According to the VMware documentation [1], vSAN HCI Mesh is a feature of vSAN that enables the allocation of storage from one vSAN enabled vSphere cluster to another, allowing for the sharing of resources between clusters. This is particularly useful in scenarios such as the one described, where additional storage needs to be allocated from another vSAN enabled cluster. [1] https://docs.vmware.com/en/VMware-vSphere/7.0/vsphere-esxi-vcenter-server-70-vsan-hci-mesh-guide.pdf

To verify object resynchronization progress and impact after a global policy change, you can use vRealize Log Insight (C). According to the VMware Official Guide, “The vRealize Log Insight dashboard can be used to verify object resynchronization progress and impact after a global policy change.”

When a host goes offline, it may cause errors on the vCenter dashboard, and the summary page of the VMs may display Noncompliant VM Storage Policies. The administrator should check the vSAN object health to identify and repair any objects that are in a non-compliant state. The following steps can be taken:

• Go to the vCenter Server's Monitor tab
• Select vSAN from the left-hand menu
• Select Skyline Health from the sub-menu
• Select Data from the sub-sub-menu
• Select vSAN object health

This will give you an overview of the vSAN object health, you can check the objects that are in a non-compliant state and use the "Repair Objects" button to repair them.

It's important to also check the reason why the host was offline, and fix it before bringing it back to the cluster.

You can also check the triggered alarms related to vSAN in Monitor -> Triggered Alarms -> vSAN object alarms, to ensure that all issues related to vSAN are resolved.

This page will display any objects that are not compliant with the storage policy and will allow the administrator to take the necessary steps to repair the objects and bring the VMs back into compliance.

The three topics that would impact the design of a new vSAN cluster to host production mission critical workloads are A. The amount of ESXi host memory, D. The size of the cache tier according to workload characteristics, and E. The supported CPU type of the ESXi host.

The amount of ESXi host memory is important because it determines the amount of memory available to virtual machines, which can impact the performance of the applications running on them.

The size of the cache tier according to workload characteristics is also important as it determines how much write buffer memory is available to the vSAN cluster. This is essential as write buffer memory helps to ensure high performance and low latency.

Finally, the supported CPU type of the ESXi host is important as this will impact the performance of the cluster, as well as compatibility with certain applications.

For more information, see the official VMware guide on vSAN cluster design: https://docs.vmware.com/en/VMware-vSphere/6.7/com.vmware.vsphere.vsan.doc/GUID-E1A6F9E6-8D6B-4F2D-A554-E8D97