[Novalug] Device naming.
Bryan J. Smith
b.j.smith at ieee.org
Mon Mar 15 22:21:14 EDT 2010
Not to cross you, but marking a partition as 8Eh (LVM [Physical Volume])
is actually is not much different than marking it 05h or 0Fh (Extended or
And in the case of only one** Physical Volume (PV), you slice it into Logical
Volumes (LVs), just like slicing an Extended Partition into Logical Partitions.
Both are disk labels with dedicated sectors for meta-data.
In the case of Extended Partitions, the header is a very simplistic, single
sector header, created when you create your first Logical Volume.
In the case of Physical Volumes, the "pvcreate" actually adds the meta-
data header (and "pvremove" explicitly removes it, so it's not seen as
a PV any more).
**Now LVM offers many advanced functions, as you know. And as you
know, you don't slice PV directly into LVs, you add it to a Volume
Group (VG). The VG is then -- as you explained -- is actually what gets
sliced. The actual slices could be located on any number of PVs in the VG.
And there are different types of LVs that can be created, including
snapshots and other things.
But keeping a 1:1 relationship for example's sake, a single PV in a single
VG, the PV gets sliced into LVs.
P.S. The hda5/sda5+ numbering for Logical Partitions in an Extended
Partition is actually a legacy Linux holdover, and other platforms and tools
don't always enumerate Logical Partitions after Primary Partitions. In
fact, Extended Partitions are actually only supposed to have up to four (4)
Logical Partitions (and several early DOS/NT kernels only support such).
It's always very important to remember Extended Partitions as a disk
label -- especially since the first Logical Partition will not begin on a perfect
boundary (because of the Extended Partition's disk label header).
----- Original Message ----
From: Peter Larsen <plarsen at famlarsen.homelinux.com>
Not at all. With LVM I don't even create a partition table. Well, for my
boot-drive I have to due to BIOS limitations, but hopefully that won't
be long. I usually "quipe" when people want to compare a logical volume
to a partition - but if it helps you understand the concept, you create
logical partitions with LVM. Logically from an admin perspective it's an
indefinite number of partitions (volumes).
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