Fixing network related issues of AWS hosted Windows servers

There are some cases when working with AWS hosted Windows systems, all of a sudden the network related issues start to trigger

These issues may relate to;

  • Lack of network connectivity.
  • Low throughput
  • No connectivity with the Windows based VPN solutions.

to fix all the above issues, you just needa to update the Para-Virtualization Drivers on Your Windows Instances.

Para-Virtualization – what is PV

Amazon Windows AMIs contain a set of drivers to permit access to virtualized hardware. These drivers are used by Amazon EC2 to map instance store and Amazon EBS volumes to their devices. We recommend that you install the latest drivers to improve stability and performance of your EC2 Windows instances.


Simply, please install / update the PV drivers for Windows

Operating System Corruption due to snapshot consolidation

There are some cases where due to VMware snapshot consolidation the VM disk systems get corrupted. I faced with the same issue on ESXi 6.5 environment. I researched on the issue and finally found out that this is a known issue on some VMWare versions. The symptoms are as follows;


  • Applications such as databases may report block-level data inconsistency.
  • Guest operating systems may report file system metadata inconsistencies
  • The VM fails to boot when it is running from an SEsparse snapshot. (SEsparse is a snapshot format introduced in vSphere 5.5 for large disks, and is the preferred format for all snapshots in vSphere 6.5 and above with VMFS-6)

Affected Environments:

VMFS-5 or NFS Datastores: VMs with virtual disks >2TB and snapshots. On VMFS-5 and NFS, the SEsparse format is used for virtual disks that are 2 TB or larger
VMFS-6 Datastores: VMs with snapshots. SEsparse is the default format for all snapshots on VMFS-6 datastores.

Impacted vSphere releases: vSphere 6.5 and above with VMFS-6 and any VM with snapshots | vSphere 5.5 and above when VMs with virtual disks >2TB have snapshots.

So basically if the VM size is more than 2TB in size and the VMFS versions are VMFS5 & VMFS6, there might be data corruptions on the infrastructure.

The issue has been resolved starting from the following ESXi versions;

  • vSphere 6.7 Update 1 
  • vSphere 6.5 Patch
  • vSphere 6.0 Patch

As a workaround, disabling “IO coalescing” for SEsparse can be carried out on host system level.

for more information, please refer the KB

[source: VMware Knowledge Base]