Comments on: How to Take ‘Snapshot of Logical Volume and Restore’ in LVM – Part III

By: Tom Lovell

Tom Lovell — Sun, 09 Feb 2020 13:57:12 +0000

Your first paragraph has a somewhat misleading statement, “If source volume has a huge changes made to sum of 1GB the same changes will be made to the snapshot volume,“ In fact, the same changes will NOT be made to the snapshot. What is written to the snapshot is the data of the original LV prior to update. That is how the snapshot is a ”point in time” copy of the original LV.

By: vinci

vinci — Mon, 11 Nov 2019 22:40:36 +0000

“It is the best idea to have the same size of Source while creating a snapshot, tecmint_datas size was 10G” Generally I think this is really bad advice, especially if you want to do a backup.

If you have, let’s say, 1TB of data that you want a snapshot of, and of which let’s say a maximum of 1% (10GB) is going to change during the copying of a snapshot, then you don’t want that snapshot to be no more than 10GB.

Saying it is ‘the best idea’ to allocate the whole size of the source is really not clever. That would mean you’d need to have yet another Terabyte in the volume group just for doing a backup, let alone space you take up with the backup itself.

By: pepa65

pepa65 — Wed, 27 Feb 2019 05:31:33 +0000

In reply to Alex. The snapshot is not tecmint_datas (but tecmint_datas_snap), and indeed the snapshot is not mounted at this point. But the volume that the snapshot was taken off (tecmint_datas) was and is still mounted, and the point is to move some files to the 'original', which doesn't affect the snapshot. But if the amount of changes is larger than the storage space allows, the snapshot is (silently) dropped.

By: Alex

Alex — Wed, 27 Feb 2019 01:38:30 +0000

After the step to create the snapshot via “lvcreate”, the next step says to “Let’s add some new files into tecmint_datas”, but you cannot copy anything to it because it has not been mounted yet.

I think you’re missing the step of mounting the snapshot.

By: pepa65

pepa65 — Fri, 27 Jul 2018 14:19:37 +0000

In reply to Babin Lonston.

This can’t be right. What if you just remove the snapshot? The source volume should continue as is, with all the changes since the snapshot was made.

The merge of the snapshot means that you are “rolling back” to the snapshot, so you lose all the changes made since the snapshot. Please clarify!