Azure replication failing between source and destination despite low churn.

Question

Azure replication failing between source and destination despite low churn.

TR 0

We have a virtual machine that is being replicated from Canada Central to Canada East. We occasionally see a critical error in the replication health. We include 3 disks in the replication, a 127GB OS disk, a 128GB mostly static storage disk, and a 2TB disk that has more frequent churn.

When I look at the status of the disks I see the Pending data as follows

Disk 0 (OS): 1.0MB Pending data
Disk 1 (low churn): 0.86MB
Disk 2 (higher churn): 0.33MB

All disks are set to "High Churn" but the status of the replication health remains critical and the "Latest crash-consistent" recovery point is from 11 hours ago. The only errors that the UI is giving me are as follows

Replication is delayed due to network connectivity issues or low bandwidth availability.
The data change rate (write bytes/sec) for one or more disks of the source machine has exceeded

If neither the network or the data change rate can handle a few MB then something is seriously wrong with this service. Would anyone here have any suggestions?

Thanks for any advice.

Naveena Patlolla 4,960 Reputation points Microsoft External Staff Moderator

2025-08-13T01:35:38.6+00:00
Hi TR

Azure Site Recovery has limits on data change rates, depending on the type of disk. To see if this problem is recurring or temporary, find the data change rate of the affected virtual machine. Go to the source virtual machine, find the metrics under Monitoring, and add the metrics as shown in this screenshot:

Select Add metric, and add OS Disk Write Bytes/Sec and Data Disk Write Bytes/Sec.

Monitor the spike as shown in the screenshot.

View the total write operations happening across OS disks and all data disks combined. These metrics might not give you information at the per-disk level, but they indicate the total pattern of data churn.

Reference link:
https://learn.microsoft.com/en-us/azure/site-recovery/azure-to-azure-troubleshoot-replication#network-connectivity-problems
https://learn.microsoft.com/en-us/azure/site-recovery/azure-to-azure-troubleshoot-replication#network-connectivity-problems
let us know if you have any further queries. I’m happy to assist you further.

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Naveena Patlolla 4,960 Reputation points Microsoft External Staff Moderator

2025-08-13T01:35:38.6+00:00

Hi TR

Azure Site Recovery has limits on data change rates, depending on the type of disk. To see if this problem is recurring or temporary, find the data change rate of the affected virtual machine. Go to the source virtual machine, find the metrics under Monitoring, and add the metrics as shown in this screenshot:

Select Add metric, and add OS Disk Write Bytes/Sec and Data Disk Write Bytes/Sec.

Monitor the spike as shown in the screenshot.

View the total write operations happening across OS disks and all data disks combined. These metrics might not give you information at the per-disk level, but they indicate the total pattern of data churn.

Reference link:
https://learn.microsoft.com/en-us/azure/site-recovery/azure-to-azure-troubleshoot-replication#network-connectivity-problems
https://learn.microsoft.com/en-us/azure/site-recovery/azure-to-azure-troubleshoot-replication#network-connectivity-problems
let us know if you have any further queries. I’m happy to assist you further.

If the comment was helpful, please click "Upvote"

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Azure replication failing between source and destination despite low churn.

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