[linux-lvm] what is free space in LVM

[Angelo Moreschini]

Hi,

I am new to LVM and I would like to have an exact answer to the question :

what is the criteria that allows to distinguishes the "free space" on the
all the space in a Volume Group?

or (if you prefer)...

how the command pvscan does to obtain information about the free space in
LVM ?

------------
According to my current knowledge, I know that the definition of "free
space" concerns with with the set of blocks for which, in the FAT, is not r
egistered a significant link to access a file.

But I think that in the context of LVM there should be a different criterion to
define the "free space" inside a Volume Group.
----------

Thank you

Regards

Angelo

[Mauricio Tavares]

Post by Angelo Moreschini
Hi,
what is the criteria that allows to distinguishes the "free space" on the

all the space in a Volume Group?

Post by Angelo Moreschini
or (if you prefer)...
how the command pvscan does to obtain information about the free space

in LVM ?
This may sound like a naive reply but I always thought free space in
a VG is space not allocated to its LVs.

Post by Angelo Moreschini
------------
According to my current knowledge, I know that the definition of "free

space" concerns with with the set of blocks for which, in the FAT, is not
registered a significant link to access a file.

Post by Angelo Moreschini
But I think that in the context of LVM there should be a different

criterion to define the "free space" inside a Volume Group.

Post by Angelo Moreschini
----------
Thank you
Regards
Angelo
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[Zdenek Kabelac]

Hi,
what is the criteria that allows to distinguishes the "free space" on the all
the space in a Volume Group?
or (if you prefer)...
howthe command pvscan does to obtain information about the free space in LVM ?
------------
According to my current knowledge, I know that the definition of "free space"
concerns with withthe set of blocks for which, in the FAT, is not registered
a significant link to access a file.
But I think that in the context of LVM there should be a different criterion
to define the "free space" insidea Volume Group.
----------

lvm2 is NOT filesystem

lvm2 is 'volume manager' - thus every PV is divided into extents.
And 'extent' could be associated with LV.

So easily - if PV has 32bit #extent count.
(Size of extent is again 32bit number -> in total 64bit address space).

So when you calc all extents in use (being member of any LV),
and subtracts this from number of all available extent
you will get number of 'free' extent.

Note - you put filesystem ON your LV - and then filesystem is managing free
space within this LV.

Zdenek