On 02/15/2014 10:12 AM, Robert P. J. Day wrote:
at this point, before i go any further, if my math is correct, is
there some command that can be used to ask, "if i *tell* you that a PV
started at this offset, and the first part of it is trashed, can you
tell me what you can find in the *rest* of the PV if it should contain
valid LVs further down"?
All of the LVM metadata is at the beginning of the PV, so it's been
trashed. The rest is just raw content -- nothing specific to LVM.
You can see this for yourself fairly easily. First, create a large
sparse file to use as your volume.
dd if=/dev/null bs=1k seek=1024k of=/var/tmp/test.img
That creates a 1GB file that currently uses no space on the disk.
# losetup -f --show /var/tmp/test.img
/dev/loop0
# pvcreate /dev/loop0
Physical volume "/dev/loop0" successfully created
# vgcreate testvg1 /dev/loop0
Volume group "testvg1" successfully created
# lvcreate -l 25%FREE testvg1
Logical volume "lvol0" created
# lvcreate -l 100%FREE testvg1
Logical volume "lvol1" created
# echo "Start of testvg1-lvol0" >/dev/testvg1/lvol0
# echo "Start of testvg1-lvol1" >/dev/testvg1/lvol1
At each stage you can run "hexdump -C /var/tmp/test.img | less"
and see what shows up there. Beyond the first 384 sectors (offset
0x30000), the only non-zero lines will be the output from those
two "echo" commands.
--
Bob Nichols "NOSPAM" is really part of my email address.
Do NOT delete it.
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