[Gllug] Come a cropper with LVM

[Bruce Richardson]

On Thu, Mar 19, 2009 at 12:48:21PM +0000, David wrote:
> Bruce Richardson wrote:
> > On Thu, Mar 19, 2009 at 12:07:36PM +0000, David wrote:
> >> The disk layout:
> >> There are three physical Volume Groups (p1, p2, p3). p1 (sda2) and p2
> >> (sda3) are primary partitions on the same physical drive, contain
> >> multiple logical volumes and free spaces. p3 is constructed from two
> >> logical partitions within a single extended partition on a single drive,
> >> but on physically separate areas of the disk, and consists of a single
> >> logical volume (LVsrv) and (currently) a little free space.
> > 
> > Erm, this sounds confused to me.  Are p1, p2 and p3 physical volumes or
> > volume groups?  You don't seem to be clear about the difference.  I'm
> > guessing that you mean volume groups, looking at the description of p3.
> > But it doesn't make much sense even if they are volume groups;  why
> > didn't you just create a bunch of PVs and make one single VG from them?
> 
> 
> Bruce,
> 
> Sorry to be confusing:
> p1, p2, and p3 are individual and separate Volume Groups
> p1 is a single physical volume

You mean it contains a single physical volume.  A volume group *is not*
a PV: it consists of one or more pvs and creates a storage pool out of
all the blocks made available to it by those PVs.

> p2 is another single physical volume
> p3 is made up of two physical volumes
> 
> I'm not sure that I had a good reason for having multiple VGs instead of
> just one: questionable logic or a learning experience way-back-when?

Questionable logic; since these PVs are on the same disk, there's really
no gain at all from having different VGs and you suffer a space
limitation that you would not have if you had unified the PVs into a
single VG.  If you had multiple PVs on multiple disks, then there can be
an argument for having one PV from each disk in each VG (but there are
other ways to enjoy RAID-like performance benefits in LVM).

-- 
Bruce

I unfortunately do not know how to turn cheese into gold.
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