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johhny B
Asked: 2017-03-09 11:31:38 +0800 CST

LVM Snapshot mapping into new logical volume that's bigger

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If I create a snapshot say:

lvcreate --size 100M --snapshot --name homeSnap /dev/vg1/home

then i back up this snapshot:

dd if=/dev/vg1/homeSnap of=/mnt/data/backup.img

then create a new logical volume

lvcreate --size 50G --name test vg1

then copy the snapshot to the new logical drive:

dd if=/mnt/data/backup.img of=/dev/vg1/test

Now say that the original /dev/vg1/home is only 10G size. The /dev/vg1/test is 50G. What happens to the other 40G will i be able to use this as normal or does the new /dev/vg1/test only become 10G and I lose the 40G without some type of resizing?

backup lvm

1 Answers

  1. Best Answer

    It of course depends on whatever you have on the /dev/vg1/homeSnap volume. But most filesystems will not automatically resize, you must issue a command to resize the filesystem.

    In a comment you mentioned XFS, the command you want is xfs_growfs, I believe maybe xfs_growfs /dev/vg1/test in your situation.

    One other thing you might need to watch out for is that some filesystems have a unique ID, and if you try to mount two copies of the filesystem that have the same unique ID you can have problems. I am not sure about the current state, but in the past XFS required special steps like generating a new ID, or passing a mount option to ignore the ID.

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