[linux-lvm] Does LVM always do 'dm suspend' when lvcreating a thin snapshot?

[Mike McCracken]

When creating a thin snapshot of a thin volume, does LVM always freeze the
FS?

I see when I run lvcreate with -vvv that it sends the 'dm suspend' message
to the origin lv, but on looking at the code I wasn't quite able to
convince myself that it will always do that, or under what circumstances it
won't.

Thanks,
-mike

[Zdenek Kabelac]

When creating a thin snapshot of a thin volume, does LVM always freeze the FS?
I see when I run lvcreate with -vvv that it sends the 'dm suspend' message to
the origin lv, but on looking at the code I wasn't quite able to convince
myself that it will always do that, or under what circumstances it won't.

Hi

Yes - suspend of thin's snapshot origin is always enforced
as you normally want snapshot FS to be in consistent state.

Zdenek

[Mike McCracken]

OK, thanks for confirming!
I'd like to help improve the documentation about this - did I miss a place
where it was mentioned explicitly? If not, where would a discussion of FS
suspending fit? I'm happy to contribute a patch.

Post by Zdenek Kabelac

When creating a thin snapshot of a thin volume, does LVM always freeze the FS?
I see when I run lvcreate with -vvv that it sends the 'dm suspend' message to
the origin lv, but on looking at the code I wasn't quite able to convince
myself that it will always do that, or under what circumstances it won't.

Hi
Yes - suspend of thin's snapshot origin is always enforced
as you normally want snapshot FS to be in consistent state.
Zdenek
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