GutoVeronezi commented on issue #6836:
URL: https://github.com/apache/cloudstack/issues/6836#issuecomment-1285524454

   Hello, @whitetiger264
   
   KVM disk snapshots in ACS are divided in two processes: take the snapshot, 
and backup the snapshot to the secondary storage.
   
   In ACS 4.17.0.0, a new way of taking disk snapshots for KVM was introduced 
(you can read the full specification in #5124). In this new process, a delta is 
created for the disk, the base file is copied to the snapshot directory in the 
primary storage `<primary-storage-path>/snapshots/<snapshot-uuid>` (which 
generates data transference between the KVM host and the primary storage), and 
the delta is merged to the base file. Then, if the first process finishes with 
success, the second process is executed according to your configuration. Here 
follows a diagram of the create snapshot process:
   
   ![Proposed Create Snapshot 
Workflow](https://user-images.githubusercontent.com/38945620/128731100-e186239e-a1e1-4e07-ba9b-fdd92e390e14.jpeg)
   
   The timeout error you see in the MS is related to the job that waits for the 
result from the agent; in the KVM agent, the process keeps running (as there is 
no timeout configured for the copy base file step) and finishes successfully as 
we can see in 
https://github.com/apache/cloudstack/issues/6836#issuecomment-1283521520. 
Therefore, it took more than 1 hour to copy the file 
`635fd5b5-bf14-4cf4-979c-be8a649d5189` (15G) to the snapshot directory and the 
job in the MS expired.
   
   In https://github.com/apache/cloudstack/issues/6836#issuecomment-1283540475 
you said that your KVM host and the MS are connected via public network. The 
KVM host and the primary storage are also connected via public network? What is 
the bandwidth of the connection between the KVM host and the primary storage?


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