On Fri, 07 Sep 2012 13:27:15 +0530, "M. Mohan Kumar" <mo...@in.ibm.com> wrote:
> On Fri, 07 Sep 2012 09:35:10 +0300, Itamar Heim <ih...@redhat.com> wrote:
> > On 09/07/2012 08:21 AM, M. Mohan Kumar wrote:
> > > On Thu, 6 Sep 2012 18:59:19 -0400 (EDT), Ayal Baron <aba...@redhat.com> 
> > > wrote:
> > >>
> > >>
> >
> > >
> > > For start using the LVs we will always do truncate for the required
> > > size, it will resize the LV. I didn't get what you are mentioning about
> > > thin-provisioning, but I have a dumb code using dm-thin targets showing
> > > BD xlators can be extended to use dm-thin targets for thin-provisioning.
> > 
> > so even though this is block storage, it will be extended as needed? how 
> > does that work exactly?
> > say i have a VM with a 100GB disk.
> > thin provisioning means we only allocated 1GB to it, then as the guest 
> > uses that storage, we allocate more as needed (lvextend, pause guest, 
> > lvrefresh, resume guest)
> > 
> > 
> When we use device=lv, it means we use only thick provisioned logical
> volumes. If this logical volume runs out of space in the guest, one can
> resize it from the client by using truncate (results in lvresize at the
> server side) and run filesystem tools at guest to get added space.
> But with device=thin type, all LVs are thinly provisioned and allocating
> space to them is taken care by device-mapper thin target
> automatically. The thin-pool should have enough space to accomoodate the
> sizing requirements. 
As of now BD xlator supports only working with linear Logical volumes,
they are thick provisioned. gluster cli command "gluster volume create"
with option "device=lv" allows to work with logical volumes as files.

As a POC I have a code(not posted to external list), with option
"device=thin" to gluster volume create command it allows to work with
thin provisioned targets. But it does not take care of resizing
thin-pool when it reaches low-level threshold. Supporting thin targets
is in our TODO list. We have dependency on lvm2 library to provide apis
to create thin-targets.


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