@olivierlambert Thanks a lot.
The Max vCPU was larger than the Physical CPU. Now it migrates successfully.

Thanks for your quick response.
My host has 4 vCPU and the VM is just 1 vCPU as shown in the screenshot.

Re: Trying to migrate

I tried to migrate VM from host1 to host2 it failed. the error message in log is:

vm.migrate
{
  "vm": "08e2baeb-0e58-c037-0e63-97b3cf41871a",
  "mapVifsNetworks": {
    "cbc74384-2167-a72f-f707-52d7179b76c3": "fab39b68-c54e-d23a-2e21-9e905f6dbbe9"
  },
  "migrationNetwork": "b0123e39-89e2-0fd6-47dc-5509552d1615",
  "sr": "bf8ec472-f0d5-1a0f-946f-97b854c6f82d",
  "targetHost": "5e57c2a7-5894-4116-bfbe-241eba3e9da3"
}
{
  "code": 21,
  "data": {
    "objectId": "08e2baeb-0e58-c037-0e63-97b3cf41871a",
    "code": "HOST_NOT_ENOUGH_PCPUS"
  },
  "message": "operation failed",
  "name": "XoError",
  "stack": "XoError: operation failed
    at operationFailed (/usr/local/lib/node_modules/xo-server/node_modules/xo-common/src/api-errors.js:21:32)
    at file:///usr/local/lib/node_modules/xo-server/src/api/vm.mjs:578:15
    at Xo.migrate (file:///usr/local/lib/node_modules/xo-server/src/api/vm.mjs:564:3)
    at Api.#callApiMethod (file:///usr/local/lib/node_modules/xo-server/src/xo-mixins/api.mjs:445:20)"
}

@olivierlambert
Thank you very much for your assistance. Unfortunately, I have encountered another issue that I would like to address. I have forgotten the password for the XOA VM , but I do have the root password.

@Rashid @BenjiReis @olivierlambert
I appreciate your patience and guidance throughout the process. I am pleased to inform you that I have successfully completed the task at hand. However, I encountered two issues along the way. Firstly, one of my SMB Storage was corrupted and was not disconnecting properly. Secondly, the system was stuck in a restart loop. After resolving the SMB storage problem, I was able to restart the system and successfully add the new host to the existing pool.
Thanks all.

@BenjiReis @olivierlambert Thanks for your response. I have run the yum update & yum upgrade in both servers. no package is available.
And I think the problem is that both servers are Master, Am I correct?

@olivierlambert Thanks for your response. I have run the yum update & yum upgrade in both servers. no package is available.
And I think the problem is that both servers are Master, Am I correct?

I currently own two Dell Servers, one being the R710 with dual CPUs and 16 GB of RAM, and the other being the R20 with a single CPU and 32 GB of RAM. Recently, I installed XCP-ng 8.2.1 on both servers. After the installation was complete, each server became a master by default, resulting in two separate pools. However, I would like to have only one pool with one master and have my R720 server act as a slave in that pool. I have attempted various methods to resolve this issue, but unfortunately, none have been successful. It is worth mentioning that both of my XCP-ng installations are up to date. Please find the attached error log and screenshot for further reference.
Thank you in Advanced.

pool.mergeInto
{
  "sources": [
    "b341a66a-6ec2-2c61-300a-2675b0edb575"
  ],
  "target": "5b11bc18-bb1f-93b5-62f9-1d45a2c69179",
  "force": true
}
{
  "code": "POOL_JOINING_HOST_MUST_HAVE_SAME_DB_SCHEMA",
  "params": [
    "5.603",
    "5.602"
  ],
  "call": {
    "method": "pool.join_force",
    "params": [
      "10.87.5.205",
      "root",
      "* obfuscated *"
    ]
  },
  "message": "POOL_JOINING_HOST_MUST_HAVE_SAME_DB_SCHEMA(5.603, 5.602)",
  "name": "XapiError",
  "stack": "XapiError: POOL_JOINING_HOST_MUST_HAVE_SAME_DB_SCHEMA(5.603, 5.602)
    at Function.wrap (file:///usr/local/lib/node_modules/xo-server/node_modules/xen-api/_XapiError.mjs:16:12)
    at file:///usr/local/lib/node_modules/xo-server/node_modules/xen-api/transports/json-rpc.mjs:35:21
    at runNextTicks (node:internal/process/task_queues:60:5)
    at processImmediate (node:internal/timers:447:9)
    at process.callbackTrampoline (node:internal/async_hooks:130:17)"
}