On 02/15/2014 10:12 AM, Robert P. J. Day wrote:
i would think it would be simpler than that -- here's the top part
of the backup file:
===== start =====
... snip ...
description = "Created *after* executing '/usr/sbin/pvscan --cache --activate ay /dev/block/8:21'"
creation_host = "localhost.localdomain" # Linux localhost.localdomain 3.11.10-301.fc20.x86_64 #1 SMP Thu Dec 5 14:01:17 UTC 2013 x86_64
creation_time = 1388764989 # Fri Jan 3 11:03:09 2014
vg1 {
id = "T8PpR6-Dh0C-3rpj-HRkh-6T9E-0r3f-YNZjVL"
seqno = 7
format = "lvm2" # informational
status = ["RESIZEABLE", "READ", "WRITE"]
flags = []
extent_size = 8192 # 4 Megabytes
max_lv = 0
max_pv = 0
metadata_copies = 0
physical_volumes {
pv0 {
id = "Yc26dN-mfSd-sGGf-Q9KU-OutY-sJgM-4P74WB"
device = "/dev/sdb5" # Hint only
status = ["ALLOCATABLE"]
flags = []
dev_size = 1400690688 # 667.901 Gigabytes
pe_start = 384
pe_count = 170982 # 667.898 Gigabytes
}
}
===== snip rest of file =====
because this disk represented pretty much a default fedora
installation, i'm assuming that there is a first primary /boot
partition, and the remainder of the 750G drive after that was
formatted as a single physical volume (pv0), which was then assigned
to the single volume group (vg1), which was then broken up into
multiple LVs.
and from the above snippet, it would seem that physical volume pv0
started at pe_start * (4M) extent_size, or 384 * 4 = 1536M. would the
math really be that straightforward? is the above telling me that the
single PV on that drive used to start at, effectively, 1.5G?
No. That would be where the allocatable extents start _within_ the PV.
When I look at one of my VGs, a PV that is in /dev/sda10 (near the
end of the disk) shows that same "pe_start = 384". I'm not sure what the
units are, but the "Bad block HOWTO" at
http://smartmontools.sourceforge.net/badblockhowto.html
contains this snippet:
"The physical partition used by LVM2 is divided in PE (Physical
Extent) units of the same size, starting at pe_start' 512 bytes
blocks from the beginning of the physical partition."
Indeed, if I run "losetup -f --show -o $((384*512)) /dev/sda10", then
"file -s /dev/loop0" finds an ext2 filesystem there.
> note: remember that the MBR was trashed as well -- it contains info
> about an alleged 2G bootable image. if i *know* the offset of the
> (damaged) physical volume, i guess i can always go into fdisk and
> simply adjust the MBR to define a "Linux LVM" partition at precisely
> that offset so i have at least a special device file that now
> (theoretically) corresponds to the original PV. does that make sense?
Yes, exactly. The trick is knowing where the PV starts, and you don't
know that yet.
--
Bob Nichols "NOSPAM" is really part of my email address.
Do NOT delete it.
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