[Linux-cluster] pool and LVM, and changes since 2000
Heinz Mauelshagen
mauelshagen at redhat.com
Thu Oct 7 09:04:05 UTC 2004
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 LVM does volume management today, and pool is obsolete.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 at coraid.com>
>
> --
> Linux-cluster mailing list
> Linux-cluster at redhat.com
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--
Regards,
Heinz -- The LVM Guy --
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Heinz Mauelshagen Red Hat GmbH
Consulting Development Engineer Am Sonnenhang 11
56242 Marienrachdorf
Germany
Mauelshagen at RedHat.com +49 2626 141200
FAX 924446
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