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Re: [Linux-cluster] pool and LVM, and changes since 2000



On Wed, Oct 06, 2004 at 10:36:41AM -0400, Ed L Cashin wrote:
> In his 2000 OLS talk, Ken Preslan talks about some older software like
> "pool" and "memexp".  I want to make sure I understand how things have
> changed since 2000.  Are the following paragraphs correct?
> 
>   Pool is software that the GFS folks created before LVM was ready.
>   LVM does volume management today, and pool is obsolete.

Well, pool is still in production use but will be substituted by CLVM
further down the road. CLVM is a superset of LVM2 and you can download it
with the LVM2 archive. It comes with builtin pool support, so that migrations
to CLVM from pool are going to happen smoothly.

>   
>   One of the features of pool that he mentions is also in LVM:
>   identifying physical block devices by their contents instead of
>   their location.  The example he gives is of a SCSI drive in a
>   fiber channel network, where adding a drive in one room can change
>   the LUN of a drive in another room.  Pool allowed tracking of
>   drives regardless of their location.  LVM does the same thing.

Yes. Everything is identified using UUIDs (PVs, VGs, LVs).
UUIDs on PVs give you location independency of drives.

> 
>   The memexp locking module that was new at the time of the 2000 OLS
>   talk was designed to use RAM exported by fancy storage hardware for
>   coordinating locking.  A single node could stand in, though, taking
>   the place of the fancy RAM-exporting storage hardware.  Today, most
>   GFS installations use DLM instead.
> 
>   Preslan mentions that after acquiring a lock, a node must "heartbeat
>   the drive" because the locking state is on the storage hardware.
> 
> How is that done these days?  Does a lock owner heartbeat the lock
> master or does cluster management take care of this issue?
> 
> -- 
>   Ed L Cashin <ecashin coraid com>
> 
> --
> Linux-cluster mailing list
> Linux-cluster redhat com
> http://www.redhat.com/mailman/listinfo/linux-cluster

-- 

Regards,
Heinz    -- The LVM Guy --

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Heinz Mauelshagen                                 Red Hat GmbH
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Mauelshagen RedHat com                            +49 2626 141200
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