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Re: [linux-lvm] VGDA Question



Rik Herrin wrote:

Hi,
According to the LVM man page, the VGDA (Volume Group
Descriptor Area) holds the metadata responsible for
keeping information about the LVs.  However, it is
contained in the PVs.  Why does the VGDA contain both
LV descriptors and PE descriptors?

Because there are LV's with PE's and both types of information must be stores somewhere.

 Shouldn't it just
have PE descriptors and leave the LV descriptors to
the volume group ?

The VGDA is where the volume group information is stored. The LV info is therefore exactly where it belongs.

 Also, when booting, what makes the
kernel know that there are VGs and LVs?

The vgscan command is run during boot (from a rc file) and it detects the volumegroups and makes them available.

 Does it look
at the type of the partition and if it detects that
it's a PV, extract the VGDA to help it build this
information?

Yes

 If this is so, how does it deal with
entire harddisks.  For example, if I run the command:
pvcreate /dev/sdd
how would the kernel know that this is a PV?.
If you use the enire harddisk, then there is no traditional partition table. In this case the vgscan command looks if the entire disk is a PV.

Finally, where exactly is the VGDA information held?.

At the beginning of the disk/partition you created with pvcreate.

Markus

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