Re: LVM

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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 <lists@xxxxxxxx> 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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