[linux-lvm] CoW under the hood

Far Had farhadk.it at gmail.com
Mon Dec 3 06:17:42 UTC 2018

I'm trying to understand how LVM thick snapshots work under the hood. I can
see that when new write requests are comming to the original volume that
has a snapshot, the current contents of storage blocks copy to the snapshot
space then the new data overwrites on the volume. No problem so far.
the question is when I delete a file on a volume that has snapshot, the
content is gone on the volume so the pointer which points from volume
object to that certain blocks on the volume should now point to empty
blocks. On the other hand I can see that the contents of deleted parts from
the original volume did not copy to the snapshot space, meaning that the
snapshot pointers that were pointing to that blocks on the original volume,
still point that direction.
In other words the pointers from both snapshot and original volume are
pointing to the same blocks on the storage media but they don't show the
same contents when you mount them on the filesystem.
Please enlighten me about this situation
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