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What Causes Hyper-V Replication Failures?

Hyper-V replication failures happen rarely, but their impact can exist catastrophic when they do. Know the scenarios that are probable to trigger a replication failure.

Over the years, I have developed something of a love/hate relationship with Hyper-V replication. On one manus, replication is one of my favorite Hyper-V features. Since my own production environment is not big plenty to justify me building a Hyper-5 cluster, I utilise replication every bit a way to protect myself confronting a host-level failure.

But as much equally I may similar the Hyper-5 replication characteristic, information technology occasionally fails pretty catastrophically.

The way that Hyper-V replication is supposed to work is whenever a block is changed inside a virtual hard deejay that is configured for replication, that cake is replicated to another host during the next replication bicycle. What happens sometimes, nevertheless, is that the synchronization process just comes to a terminate.

There is usually a corresponding error message that says, "Hyper-V suspended replication for virtual machine <VMName> due to a non-recoverable failure. (Virtual Car ID <VMId>). Resume replication afterwards correcting the failure." When this happens, Hyper-V lets you right-click on the virtual machine and choose a Resume Replication control from the shortcut menu. Sometimes this fixes the problem, but other times it is incommunicable to resume virtual motorcar replication.

When that happens, there is little that can be washed besides disabling replication, deleting the replica and then setting upwards replication from scratch. This puts the virtual auto at hazard until its entire contents can exist resynchronized.

And then what causes these replication failures? Unfortunately, I don't have a definitive respond. I've searched TechNet for an explanation whenever I have experienced this problem in the past, but take always come upwardly empty-handed. Even so, I think that I might have finally figured out what is going on.

I take been having problems with periodic replication failures for as long as the replication characteristic has existed. The problems have go far less frequent over time, which I attribute to Hyper-Five condign more mature. Today, Hyper-5 replication failures are kind of a rarity (at least in my organization), but I have noticed that there are a couple of things that seem to happen just before a replication failure.

One of the events that seems to trigger a replication failure is a Hyper-V outage. Last autumn, for example, I found myself in the projected path of a hurricane. In preparation for the hurricane, I shut down my replica server and stored it somewhere condom. When I somewhen brought the server dorsum online, however, I had to bargain with an irrecoverable replication failure. I will concede that the timing of this failure could peradventure be a coincidence -- but I don't think so.

The other thing that seems to cause replication failures is copying large amounts of data to a virtual machine. About a twelvemonth ago, for example, I had to copy simply under 3TB of data to a virtual file server. Shortly thereafter, the replication process stopped working.

I take long held theories as to why these two types of events might trigger replication failures, just I have always resisted the temptation to write about them because all of the evidence in support of my theories was coexisting at best. I causeless that the replica was simply being overloaded with replication data, and that replication would fail because the replication process could not be completed within a single bicycle. Again, this was simply a theory.

This morn, all the same, I accidentally stumbled onto an interesting TechNet article while looking for something else. The article, which yous can read here, lists two reasons why this blazon of replication failure occurs.

The get-go reason is insufficient storage space. However, I accept e'er had enough of free storage space when failures have occurred in my environment, so that explanation does not account for my problems.

The second reason is that a power failure has occurred on the replica side and the replica server was restarted. The article goes on to explain that data that needs to be replicated tin can accumulate while the replica server is offline. When the server comes back online, replication fails because the bandwidth is inadequate to handle the volume of data that needs to exist replicated.

This explanation seems to fit both of my suspected replication failure triggers. The TechNet article says indicate-blank that replication can fail if the replica server is disconnected and then restarted. Still, it also seems plausible that trying to copy massive amounts of data to a virtual automobile could overwhelm the available bandwidth, resulting in a replication failure. Hopefully, this explanation volition shed some lite on the state of affairs for anyone else who may take been struggling with replication failures.

Most the Author

Brien Posey is a 20-time Microsoft MVP with decades of IT experience. Every bit a freelance writer, Posey has written thousands of articles and contributed to several dozen books on a wide variety of IT topics. Prior to going freelance, Posey was a CIO for a national chain of hospitals and health intendance facilities. He has too served as a network ambassador for some of the state's largest insurance companies and for the Department of Defence at Fort Knox. In addition to his continued work in Information technology, Posey has spent the last several years actively grooming as a commercial scientist-astronaut candidate in preparation to fly on a mission to report polar mesospheric clouds from infinite. You can follow his spaceflight training on his Spider web site.

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Source: https://redmondmag.com/articles/2019/05/16/hyperv-replication-failure-causes.aspx

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