Cloud Wiki Notes

 What is Multipathing and Failover

To maintain a constant connection between a host and its storage, ESXi supports multipathing. Multipathing is a technique that lets you use more than one physical path that transfers data between the host and an external storage device.

In case of a failure of any element in the SAN network, such as an adapter, switch, or cable, ESXi can switch to another physical path, which does not use the failed component. This process of path switching to avoid failed components is known as path failover.

In addition to path failover, multipathing provides load balancing. Load balancing is the process of distributing I/O loads across multiple physical paths. Load balancing reduces or removes potential bottlenecks.

Note

Virtual machine I/O might be delayed for up to sixty seconds while path failover takes place. These delays allow the SAN to stabilize its configuration after topology changes. In general, the I/O delays might be longer on active-passive arrays and shorter on active-active arrays

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CONSOLIDATE SNAPSHOT:

Consolidate Snapshot is a new function in the later versions of vSphere which will merge ALL the snapshots into the Parent VMDK file.

Snapshot consolidation is useful when snapshot disks fail to compact after a Delete or Delete all operation or if the disk did not consolidate. This might happen, for example, if you delete a snapshot but its associated disk does not commit back to the base disk.

The snapshot Consolidation  searches for hierarchies or delta disks to combine without violating data dependency. After consolidation, redundant disks are removed, which improves virtual machine performance and saves storage space.

When initiating a snapshot delete action, the delta disk changes are then written to the base or parent VMDK file and the snapshot is deleted. With vSphere 5, a new option called consolidate was introduced. The purpose of consolidate is if the snapshot deletion process was not successful. In the past there were incidents where a user would initiate a snapshot deletion thinking the snapshot got deleted, yet to find out later that that’s not the case. With the consolidation option, when you initiate a snapshot deletion, if the snapshot fails to delete, the VM will then generate a warning letting you know that a consolidation is required. You would then run the snapshot consolidation option and the snapshot would get committed.

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Different versions of VMFS-5 are created by different versions of ESXi 5.x.

• ESX 3.0.0 is provided with VMFS 3.21 (initial release)
• ESX 3.5.0 is provided with VMFS 3.31
• vSphere (ESX 4.0) is provided with VMFS 3.33
• vSphere (ESX 4.1) is provided with VMFS 3.46
• vSphere (ESXi 5.0) is provided with VMFS 5.54

5.0 - 5.54
5.1 - 5.58
5.5 - 5.60

ESXi 6.0

6.0 - 5.61

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Connecting to a virtual machine console fails with the error: The VMRC Console has Disconnected. Trying to reconnect (2050470)

Symptoms

• Attempting to connect to a virtual machine console fails.
• The VMRC session can be opened with the vSphere Web Client, but not with the vSphere Client.
• You see the error :
  
  Error: The VMRC Console has Disconnected.. Trying to reconnect
  

Cause

This issue occurs due to an Application Control software such as antivirus Software that has the ability to block certain applications or functions of installed software on client/server systems.

Note: Depending on antivirus architecture it is necessary to have access to web GUI of the security server or hosted portal to disable certain settings.

Resolution

To resolve this issue, use one of these options:

• Disable application control for virtual applications through the antivirus software.
• Uninstall and reinstall the vSphere Client.
• Stop the vmware-vmrc.exe*32 service from Windows Task Manager and then log in again.

Link: 

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