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vultr live snapshots
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vultr live snapshots

Hi,

With Vultr you can take a snapshot of a running vps. What happens if the disk is modified while the snapshot is occurring? (Say a database transaction that occurs in between the start of the snapshot and the end?) Does the snapshot process "freeze" the VPS until the snap is over, to maintain consistency? Any ideas? I could, of course, as them but I thought I would hit up the LET crowd first.

-Adam

Comments

  • jarjar Patron Provider, Top Host, Veteran

    I think the safe assumption is that anything receiving constant writes during the process may be corrupted, but it's probably a good idea to ask their support for clarification. Just imagine an InnoDB database receiving constant changes during a live backup of the data, for example.

  • ExpertVMExpertVM Member, Host Rep

    I would highly recommend that you do a SQL dump as a second layer of backup protection

    Thanked by 1yomero
  • I guess just running a DB dump before the snapshot will do the trick. I will ask Vultr and see what they have to say.

  • you should shutdown the vps before doing the snapshot.

  • Someone (a non-staff member) on the vultr forums said this :

    a snapshot freezes the filesystem, redirects all system writes elsewhere temporarily,
    It copies the frozen filesystem somewhere,
    it then unfreezes the filesystem, overlays the writes that happened in the meantime,
    Continues on as normal.

    in other words, the snapshot is of that instant, and is not inconsistent.

  • @AdamM said:
    Someone (a non-staff member) on the vultr forums said this :

    a snapshot freezes the filesystem, redirects all system writes elsewhere temporarily,
    It copies the frozen filesystem somewhere,
    it then unfreezes the filesystem, overlays the writes that happened in the meantime,
    Continues on as normal.

    in other words, the snapshot is of that instant, and is not inconsistent.

    Is this r1 I wonder or something else. It sounds non trivial for sure

  • sidewinder said: Is this r1 I wonder or something else. It sounds non trivial for sure

    Agreed, sounds very complex to implement correctly.

    Thanked by 1raindog308
  • jarjar Patron Provider, Top Host, Veteran
    edited December 2016
  • perennateperennate Member, Host Rep

    The snapshot will be a consistent state of the disk. The reason it is still recommended to shutdown the VPS is because the filesystem may still be in an inconsistent state wrt the parts of the filesystem that have been written to disk.

    Thanked by 1yomero
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