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[linux-lvm] What happens with full snapshots



Hello,

I’m relatively new to lvm, I’m using Fedora for almost 3 years, but up to now I just set up lvm on install, formatted my ext3/ext4 and it just works.

Now I want to go somehow deeper playing around with snapshots.

 

I know you should size your snapshot volume to a size that can hold all the changes. As I see a snap lv only contains the “original” datachunks and the original lv is in a normal state as if there were no snapshot.

 

My questions:

1.       What happens if the snap gets full (e.g. someone copies large data from one lv to a snapshotted lv or something other you didn’t expect), some sites say it original and snapshot gets deactivated, some sites say the snap lv gets invalidated. What does this mean? Is my original volume just crap afterwards or can I work on as usual (with the difference that nothing is written on the snap anymore), or just need to remove the snap ….

2.       What happens if there is a problem with a snap? I’ve heard on reboot the snapshots are lost. What if there is a power shortage, so the snap is lost, you boot and the original lv just seeks for the snap? Are there implications on this. Can you just mount such a original lv or do you have to remove the (non existent) snap lv before (How can you remove a snapshot that doesn’t exist anymore)

 

That would be nice to know before I use snaps.

Thanks in advance,

Harald (Harry) Heigl

 


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