[linux-lvm] What is the use of thin snapshots if the external origin cannot be set to writable ?

[Gionatan Danti]

Il 2020-11-21 04:10 Sreyan Chakravarty ha scritto:
> I mean what is the point of creating a snapshot if I can't change my
> original volume ?
> 
> Is there some sort of resolution ?

External thin snapshot are useful to share a common, read-only base (ie: 
a "gold-master" image) with different writable thin lvm overlay volumes. 
They can not be merged into external origin; otherwise, a single merge 
operation would invalidate *all* other thin snapshot relying on the same 
origin.

Classical LVM snapshots are good for temporary, short-lived snapshots - 
basically taken for backup purpose only (and immediately removed after 
the backup completed). You should not use them for long-lived snapshots 
(otherwise you can see much lower performance and delayed boot).

If you want to have long-lived snapshot you should use LVM thin 
snapshots. For root volumes, you have two choices:
- use a thin lvm volume for root, which is a supported use case (but it 
will probably require a system reinstallation);
- continue using your classical LVM as a immutable base and use a thin 
lvm with external snapshot to store all new writes.

Regards.


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Danti Gionatan
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