Re: [Gluster-devel] LVM

[Onyx]

Krishna Srinivas wrote:
> Onyx,
>
> Just thinking about it, using snapshots as glusterfs storage volumes
> is not advisable unless you know what you are doing. If you roll back
> a volume, it will depend on how selfheal of unify/afr handle it. AFR
> would just update the rolled back volume with the other copy.
>   
Yes, that was what I was thinking. Newer will overwrite the older, witch 
is the rolled-back one in this case.

> Better use of LVM + glusterfs would be to grow the backend FS
> as an when needed.
>   
Yes I have been thinking of that too.
I was just  'brainstorming' on a solution to have snapshot features in 
glusterfs.

> I think use case of snapshots just in backend LVM in a glusterfs
> environment will not be much. However snapshots in a glusterfs
> as a whole filesystem will be useful.
>   
It surely would.
Now, what if I would setup a glusterfs volume with lvm on all it's 
subvolumes. It shouldn't be to hard to write something that, if I want 
to make a snapshot of the whole glusterfs filesystem, it sends my "take 
snapshot"-command to the all the lvm subvolumes and executes the actual 
lvm snapshot command over there. Or am I missing something here?



> Krishna
>
> On Sat, Jun 14, 2008 at 4:13 PM, Onyx <address@hidden> wrote:
>   
> > Hmm, yes, what was I thinking....
> >
> > But if I want to use LVM snapshots underneath glusterfs volumes (on
> > different bricks) who are then unified or afr'd,  won't there be a problem
> > because the snapshots aren't taken at exactly the same time? Or what would
> > be the expected behavior if I for example roll back one volume in an afr
> > setup and not the other?
> >
> >
> >
> >
> >
> > Anand Babu Periasamy wrote:
> >     
> > > --
> > > Anand Babu Periasamy
> > > GPG Key ID: 0x62E15A31
> > > Blog [http://ab.freeshell.org]
> > > The GNU Operating System [http://www.gnu.org]
> > > Z RESEARCH Inc [http://www.zresearch.com]
> > >
> > > Hi Onyx,
> > > GlusterFS volumes are file based. LVM requires block based
> > > store. You cannot have LVM over GlusterFS. I am assuming
> > > you are asking about GlusterFS over LVM. You can use LVM and
> > > its snapshotting ability underneath the GlusterFS posix volume.
> > > It will work transparently.
> > >
> > > --
> > > Anand Babu Periasamy
> > > GPG Key ID: 0x62E15A31
> > > Blog [http://ab.freeshell.org]
> > > The GNU Operating System [http://www.gnu.org]
> > > Z RESEARCH Inc [http://www.zresearch.com]
> > >
> > >
> > >
> > > Onyx wrote:
> > >       
> > > > Has anyone ever tested LVM on top of a glusterfs volume? Would this even
> > > > be possible?
> > > > I'm interested because of the snapshot feature of LVM.
> > > >
> > > > Thanks!
> > > >
> > > >
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