4 Replies Latest reply on Mar 18, 2016 11:52 PM by linotelera

    Query on VMware Snapshot and TCP IP connections

    sachin30 Lurker

      One of our supplier is opting for Vmware snapshots to take VM server (Windows 2012 server) backup on a daily basis. We have TCP/ IP socket processes that connect and exchange data with this server. My question is whether there would be any adverse impact on TCP/IP socket connections to the server at the moment snapshot is made? Is there possibility that these TCP/IP connections will get dropped at the time snapshot is taken?

       

      Can Users/ TCP IP processes continue to access VM during snapshot backup process?

       

      I would appreciate any help on this query. Please let me know if any other details required in order to understand the query better.

       

      regards

      Sachin

        • 1. Re: Query on VMware Snapshot and TCP IP connections
          linotelera Hot Shot
          vExpert

          Hi and welcome

          during snapshot creation process a delta file is creating and I/O virtual disk performance could be decreased. See https://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1015180

          TCP/IP performance should not be compromized except in case if it is correlated to a process that depends on disk. If your vm is a web-server it could be impacted... if your vm is a proxy server it should not. In all cases if your VM is configured using the right ratio between cpu, mem and disk and virtual nic are vmxnet3 (vmware tools is mandatory) performance loss during snapshot are very low.

           

          Answering your question: user could be use VM, but snapshot process should be don during off-peak time window.

          In all cases tcp/ip connection should not be dropped (sometime latency could be increased but never dropped).

           

          Because in most of the cases snapshot is a perfomance impact process I leave this KB: https://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1025279

          • 2. Re: Query on VMware Snapshot and TCP IP connections
            sachin30 Lurker

            Thanks linotelera for taking time to respond. The VM is database server and we have separate data replication process for backup and recovery. The snapshot backup would therefore only be used as a system/ OS level backup so that it could be stood up in case of problems with original VM.

             

            TCP/IP is a sensitive traffic. TCP/IP socket connections between 2 processes that run on different machines will be dropped immediately if a request made by the sending process is not acknowledged within a very limited timeframe by the receiving process.

             

            As mentioned, there are TCP/ IP connections that are made from another server to this database VM on which snapshot will be taken. And wanted to find out whether these connections would get dropped either at time of 'stun' or at the moment snapshot is made?

             

            Regards

            Sachin

            • 3. Re: Query on VMware Snapshot and TCP IP connections
              MKguy Virtuoso

              TCP/IP is a sensitive traffic. TCP/IP socket connections between 2 processes that run on different machines will be dropped immediately if a request made by the sending process is not acknowledged within a very limited timeframe by the receiving process.

              TCP is by definition not a "sensitive" protocol. It's entire purpose is to deal with packet loss, delays, buffer handling etc. to ensure a reliable connection stream of data for the upper application layer protocols. Modern applications and OSes typically have TCP-timeouts between multiple seconds and sometimes minutes, way more time than typically required to stun/unstun a VM.

               

              A snapshot stun/unstun cycle is completely transparent to the network stack, I have never seen "dropped" TCP connections and can't imagine why it should happen.

              You may lose a ping or 2, but this kind of delay is nothing special and entirely the reason your application is relying on TCP to deal with such cases. Basiscally it will cause the same kind of network "impact" as a vMotion.

              Just test it by connecting via RDP/SSH to your server, take a snapshot, you most likely won't notice anything and your connection will not be dropped - because the underlying TCP session is still fine.

              • 4. Re: Query on VMware Snapshot and TCP IP connections
                linotelera Hot Shot
                vExpert

                Just to say that VM snapshot could be used during backup job but it is not a backup alternative.

                Like confirmed by MKguy snapshot process does not affect to TCP/IP connection... but if db machine is doing many transaction and snapshot is made using quiesce mode it could take too long period and performance impacts disk I/O and replication process, that is not dependent to the connection, but depends on virtual disk read/write latency.

                In your case I suggest to do using san snapshot instead of vm snapshot. Depends on your storage array, a serious storage vendor offers lun snapshot features available (free or pay).

                Regards