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martinfrancis's avatar
martinfrancis
Level 3
2 years ago

instant snapshot (vxsnap) - multiple volumes - are the snapshots consistent between each other ?

Using tradition 3rd mirror break off snapshot using vxassist, when multiple volumes are specified on the snapshot command, all the volumes are split atomically and all the volumes are split exactly a...
atomic
instant snap
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point in time
vxsnap
  • sdighe1's avatar
    sdighe1
    2 years ago

    Hi Martin, 

    Your understanding is write about freeze and thaw. You can certainly recommend using vxsnap command for snapshots as I mentioned with multiple tuples of "vol/snap" entries. This works fine and we test this functional in our pipelines in almost daily fashion.

    vxsnap manpage is missing this information, which needs to be taken care. 

sdighe1's avatar
sdighe1
Level 3
2 years ago

Hi Martin,

With vxsnap command, if you take snapshot of multiple volumes in single invocation , all the file-systems involved in operation will be freezes one-by-one and then volumes snapshot is created.

This way the snapshot are exact point-in-time copy with all volumes involved.

Typically one can do this by specifying multiple tuples of "source=volname/snap=volname_snapid" or "source=volname/new=volname_snapid/cachesize=<>" or "source=volname/new=volname_snapid/cache=cache-obj-name" tuples in single command line.

e.g. vxsnap -g dg1 make source=vol1/new=vol1_snap/cache=cache_obj_1 source=vol2/new=vol2_snap/cache=cache_obj_1 .....

 

 

  • martinfrancis's avatar
    martinfrancis
    Level 3
    2 years ago

    When you say the file systems will be frozen one by one, do you mean they will be frozen one by one but they will not be thawed until the snapshot of ALL the volumes are taken - correct?
    If this is how it is done, then it is great for my use case because then ALL the volumes will be consistent from a vxfs point of view between each other.

    The reason for my original query is because on vxassist manpage it clearly documents the legacy third mirror snapshot feature: Quoting from vxassist man page.
    "The snapshot command accepts more than one volume. All the given volumes are split atomically (in a single transaction). That is, all the given volumes are relatively consistent as a result of taking the snapshot"
    The key word is "Single transaction"
    https://sort.veritas.com/public/documents/vie/8.0/linux/manualpages/html/man/volume_manager/html/man1m/vxassist.1m.html
    On the vxsnap man page or vxsnap documenation, this key piece of information is missing