[linux-lvm] LVM2 and OCFS2

[linux-lvm] LVM2 and OCFS2

[Michael Lessard]

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Hi Everyboy !

 I read that LVM2 is not cluster aware (specially with OCFS2) from different
post on internet forum... If it's true, could someone could confirm this
information and point me where i can find this affirmation in documentention
?

 I do some test with OCFS2 on LVM2 and it's seems to run correctly , so i
have some interrogation about this fact !

 If it's true that LVM2 are not cluster aware, doess anybody know how could
i run ocfs on technology who are offer similair fonctionnality ?

 Thanks in advance !

Michael

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Re: [linux-lvm] LVM2 and OCFS2

[Patrick Caulfield]

Michael Lessard wrote:
> Hi Everyboy !
> 
>  I read that LVM2 is not cluster aware (specially with OCFS2) from
> different post on internet forum... If it's true, could someone could
> confirm this information and point me where i can find this affirmation
> in documentention ?
> 
>  I do some test with OCFS2 on LVM2 and it's seems to run correctly , so
> i have some interrogation about this fact !

It's true that lvm is not cluster-aware. What that means is that if you update the volume groups on one node then the other nodes in
the cluster will not see the changes and you could end up with the block devices on the machines dangerously out of sync.

What you tried (it seems to me) is just created LVM volumes and run OCFS2 on them. that /will/ work provided you never change the
volume groups!

To get clustered LVM you need to use clvm (RPM package lvm2-cluster) which synchronises LVM metadata updates across the cluster.
This only works with Red Hat cluster suite though - you would need you write your own cluster management plugin for OCFS2 if you
wanted to use that (hard, but not impossible). Of course, RHCS does offer GFS as the cluster filesystem, if that's what you really need!

-- 

patrick

Re: [linux-lvm] LVM2 and OCFS2

[Morten Torstensen]

Patrick Caulfield wrote:
> To get clustered LVM you need to use clvm (RPM package lvm2-cluster) which synchronises LVM metadata updates across the cluster.
> This only works with Red Hat cluster suite though - you would need you write your own cluster management plugin for OCFS2 if you
> wanted to use that (hard, but not impossible). Of course, RHCS does offer GFS as the cluster filesystem, if that's what you really need!

Another option is GPFS from IBM, free as in beer. It really is a state 
of the art cluster filesystem and well worth the effort to look into if 
you are in the market for a cluster FS.

-- 

//Morten Torstensen
//Email: morten@mortent.org
//IM: Cartoon@jabber.no morten.torstensen@gmail.com

And if it turns out that there is a God, I don't believe that he is evil.
The worst that can be said is that he's an underachiever.

Re: [linux-lvm] LVM2 and OCFS2

[Nate Carlson]

On Mon, 11 Dec 2006, Morten Torstensen wrote:
> Another option is GPFS from IBM, free as in beer. It really is a state 
> of the art cluster filesystem and well worth the effort to look into if 
> you are in the market for a cluster FS.

GPFS is available for free now? I'm not finding it available for download 
anywhere - got a link?
y
------------------------------------------------------------------------
| nate carlson | natecars@natecarlson.com | http://www.natecarlson.com |
|       depriving some poor village of its idiot since 1981            |
------------------------------------------------------------------------

Re: [linux-lvm] LVM2 and OCFS2

[Michael Lessard]

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Thanks Patrick !  I appreciate and now understand why LVM are not cluster
aware !

 have good week !

Michael


On 12/11/06, Patrick Caulfield <pcaulfie@redhat.com> wrote:
>
> Michael Lessard wrote:
> > Hi Everyboy !
> >
> >  I read that LVM2 is not cluster aware (specially with OCFS2) from
> > different post on internet forum... If it's true, could someone could
> > confirm this information and point me where i can find this affirmation
> > in documentention ?
> >
> >  I do some test with OCFS2 on LVM2 and it's seems to run correctly , so
> > i have some interrogation about this fact !
>
> It's true that lvm is not cluster-aware. What that means is that if you
> update the volume groups on one node then the other nodes in
> the cluster will not see the changes and you could end up with the block
> devices on the machines dangerously out of sync.
>
> What you tried (it seems to me) is just created LVM volumes and run OCFS2
> on them. that /will/ work provided you never change the
> volume groups!
>
> To get clustered LVM you need to use clvm (RPM package lvm2-cluster) which
> synchronises LVM metadata updates across the cluster.
> This only works with Red Hat cluster suite though - you would need you
> write your own cluster management plugin for OCFS2 if you
> wanted to use that (hard, but not impossible). Of course, RHCS does offer
> GFS as the cluster filesystem, if that's what you really need!
>
> --
>
> patrick
>
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>

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Re: [linux-lvm] LVM2 and OCFS2

[Boris Ostrovsky]

(Resending with cc: fixed)

> It's true that lvm is not cluster-aware. What that means is that if you update the
> volume groups on one node then the other nodes in the cluster will not see the
> changes and you could end up with the block devices on the machines dangerously
> out of sync.

What if I can guarantee that other nodes will not access LVM metadata
(i.e. they will not issue any LVM command) until I run 'vgchange -ay'
on them? The only access that those other nodes will have to volumes
is that they will have some of them mounted.

Is this still dangerous? My (limited) understanding of metadata is
that it is stored in the first few blocks of a disk (or striped, if
necessary) and is cached in lvm.cache. vgchange will sync disk and
cache, so it should be OK, right?

Thanks.
-boris


> What you tried (it seems to me) is just created LVM volumes and run OCFS2 on
> them. that will/ work provided you never change the volume groups!

Re: [linux-lvm] LVM2 and OCFS2

[Patrick Caulfield]

Boris Ostrovsky wrote:
> (Resending with cc: fixed)
> 
>> It's true that lvm is not cluster-aware. What that means is that if
>> you update the
>> volume groups on one node then the other nodes in the cluster will not
>> see the
>> changes and you could end up with the block devices on the machines
>> dangerously
>> out of sync.
> 
> What if I can guarantee that other nodes will not access LVM metadata
> (i.e. they will not issue any LVM command) until I run 'vgchange -ay'
> on them? The only access that those other nodes will have to volumes
> is that they will have some of them mounted.
> 
> Is this still dangerous? My (limited) understanding of metadata is
> that it is stored in the first few blocks of a disk (or striped, if
> necessary) and is cached in lvm.cache. vgchange will sync disk and
> cache, so it should be OK, right?

Yes, that should work.

Just be VERY, VERY careful!

patrick