We have two environment of XCP-ng, lets say DC and DR connected over WAN.
DC and DR have multiple 3-4 XCP-ng hosts(XCP-ng 8.0) each.
We are using XO built from source. (5.42 build, xo-server 5.55.0, xo-web 5.55.0)
We are using XO for following:

• Continuous VM replication of VM from DC to DR XCP-ng host.
  This failed with the error: Error: VDI_IO_ERROR(Device I/O errors)
  As per readings and recommendations from various threads(GH and forum) related specifically to this VDI_IO_ERROR, I have added following line in config.toml on xoa machine.
  guessVhdsize = true

But this have not helped to resolve the issue.
Copying/continuous replication of VM within(intra) XCP-ng hosts of DC or DR environment works fine.
But the same operations fails when we perform them between DC and DR XCP-ng hosts.
Following errors are found in xensource.log of destination xcp-ng host:
Importing raw VDI R:<id>|vhd_tool_wrapper] vhd-tool failed, returning VDI_IO_ERROR
Importing raw VDI R:<id>|vhd_tool_wrapper] vhd-tool output: vhd-tool: Non-zero size required (either a pre-existing destination file or#012 specified via --destination-size on the command line)

Importing raw VDI R:<id>|import] Caught exception: VDI_IO_ERROR: [ Device I/O errors ]
Importing raw VDI R:<id>|taskhelper] the status of R:<id> is failure; cannot set it to `failure
VDI.import D****|backtrace] Importing raw VDI R:<id> failed with exception Server_error(VDI_IO_ERROR, [ Device I/O errors ])
VDI.import D****|backtrace] Raised Server_error(VDI_IO_ERROR, [ Device I/O errors ])
VDI.import D****|backtrace] 1/12 xapi @ xcp-10 Raised at file ocaml/xapi/vhd_tool_wrapper.ml, line 59
VDI.import D****|backtrace] 2/12 xapi @ xcp-10 Called from file lib/xapi-stdext-pervasives/pervasiveext.ml, line 24
VDI.import D****|backtrace] 3/12 xapi @ xcp-10 Called from file lib/xapi-stdext-pervasives/pervasiveext.ml, line 35
VDI.import D****|backtrace] 4/12 xapi @ xcp-10 Called from file lib/xapi-stdext-pervasives/pervasiveext.ml, line 24
VDI.import D****|backtrace] 5/12 xapi @ xcp-10 Called from file lib/xapi-stdext-pervasives/pervasiveext.ml, line 35
VDI.import D****|backtrace] 6/12 xapi @ xcp-10 Called from file ocaml/xapi/import_raw_vdi.ml, line 81
VDI.import D****|backtrace] 7/12 xapi @ xcp-10 Called from file ocaml/xapi/import_raw_vdi.ml, line 105
VDI.import D****|backtrace] 8/12 xapi @ xcp-10 Called from file ocaml/xapi/server_helpers.ml, line 80
VDI.import D****|backtrace] 9/12 xapi @ xcp-10 Called from file ocaml/xapi/server_helpers.ml, line 99
VDI.import D****|backtrace] 10/12 xapi @ xcp-10 Called from file lib/xapi-stdext-pervasives/pervasiveext.ml, line 24
VDI.import D****|backtrace] 11/12 xapi @ xcp-10 Called from file lib/xapi-stdext-pervasives/pervasiveext.ml, line 35
VDI.import D****|backtrace] 12/12 xapi @ xcp-10 Called from file lib/backtrace.ml, line 177
VDI.import D:****|backtrace]

If anybody faced similar issue and found any solution for it kindly reply to this.

@DustinB Thanks for replying, will definitely try this once.

I fetched current master and followed the same instructions that we follow for building xo from sources and start it.
The initial requirements(exact node version and other build requirements) of building from sources were in place.
The build worked fine but I was facing issues while starting the xo using yarn start.
It complains about undefined parameters. e.g. config.blockedAtOptions
As per installation instructions I copied sample-config.toml and I observed that those parameters are not present in sample-config.toml.
I found those parameters in config.toml (in packages/xo-server)
So I copied config.toml file but again I was facing some issues with that configuration file as well.
I was getting, following response in this case after login and even login page was also appearing without icons. :
Cannot GET /
this was related to checking of xo-web in wrong location.
When I hard coded path of xo-web, it worked.
If anyone have tried new master and followed same installation from sources instructions, kindly share their experiences.

@ben20ben Thanks, This works. Do you know the reason why we need to select video RAM as 16 MB instead of 8 MB?

Changed it to run after every 10 mins. I was missing the correct configuration.
Thank you very much.

We have configured backup job as follows:

I have a xo-server which is built from source and version found in CHANGELOG.md is 5.55.0.
Clocks of xo-server VM and all the xcp-ng hosts are in sync
I am trying to schedule a continuous replication job through backup menu.
The problem I am facing is this:
Continuous replication does not proceed as scheduled(after every 10 mins).
I don't see any errors in logs or in the console from where xo-server is running.
I had to manually start the continuous replication task to perform it.

I am attaching a screenshot of the scheduled continuous replication backup.