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- Tips for DAG Exchange Backup and Replication in vSphere
Tips for DAG Exchange Backup and Replication in vSphere
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This article was initially written when vSphere 5 snapshot operations were known and expected to cause small amounts of I/O stun to a VM's guest OS. Improvements in the latter vSphere versions, including significant changes to snapshot operation methodology in vSphere 6 and vSphere 7, have reduced the impact of snapshots on VM Guest OS I/O.
When using vSphre 6.x or newer, the advice in this article should only be implemented if node failover issues occur due to snapshot-induced VM Guest OS I/O stun.
Challenge
Cause
Solution
The suggestions below are general advice intended to help alleviate and prevent issues. Every environment is different, and while these settings and suggestions may work in one environment, they may have little or no impact in others. Generally speaking stability issues which occur are often environmental, and will require investigation of all components involved, both physical and software.
The suggestions below include configuration changes to VMware as well as Microsoft Exchange. Veeam is not responsible for any issues incurred after making the suggested changes. You are advised to contact and review all setting changes with the respective product support organization.
- Place the Exchange Virtual Machine's disks on the fastest available datastores.
- Disable all background scanning and/or maintenance tasks occurring in Exchange or any other tools being leveraged against the system during backup.
- Perform the Exchange Backup singularly as opposed to concurrently with other jobs.
- Review cluster failover sensitivity using this command line tool and switch.
See note below if running Server 2012 or newer.
cluster /prop
Adjust Microsoft settings for failover sensitivity (in bold, run from the command line)
cluster /prop SameSubnetDelay=2000:DWORD ::(Default: 1000 in Server 2008 R2) cluster /prop CrossSubnetDelay=4000:DWORD ::(Default: 1000 in Server 2008 R2) cluster /prop CrossSubnetThreshold=10:DWORD ::(Default: 5 in Server 2008 R2) cluster /prop SameSubnetThreshold=10:DWORD ::(Default: 5 in Server 2008 R2)
- Add the line snapshot.maxConsolidateTime = "1" to the .vmx (configuration) file for the primary node.
Please note that this is an undocumented vmx alteration and should be validated by VMware support before use. - If possible, reduce the impact of snapshot operations by reducing the total number of disks (.vmdks) for the primary node.
- If the VM resides on a datastore backed by NFS storage, consider migrating the VM to VMFS storage.
- Test snapshot operations directly to ESX(i) host instead of vCenter. (In some cases, gaps in communication between vCenter and ESX(i) host can impact snapshot operations, including VSS operation timing.)
Note: In Server 2012 or newer, cluster.exe may not be available. As such, you will need to install and use the PowerShell cmdlets. The cmdlets may need to be enabled using the following command:
Install-WindowsFeature -name RSAT-Clustering-CmdInterface
View cluster settings:
Get-cluster | fl *subnet* - provides current settings for timeout
Adjusting cluster settings:
(get-cluster).SameSubnetThreshold = 20 #(Default 10 in Windows 2012R2+) (get-cluster).SameSubnetDelay = 2000 #(Default 1000 in Windows 2012R2+) (get-cluster).CrossSubnetThreshold = 40 #(Default 20 in Windows 2012R2+) (get-cluster).CrossSubnetDelay = 4000 #(Default 1000 in Windows 2012R2+)
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