Q: how is 'dd' like motorcycles ?
A: there are 2 types of users, those who have crashed, and those who will.
Well, Ive now joined the ranks of folks who have. I blew away the hda partition table.
/dev/hda4 used to have a good PV.
Miraculously, Ive successfully recovered hda[1-3], by a combination of luck,
a simple partition table (1=vfat, 2=swap, 3=ext2, 4=lvm, on cylinder boundaries), good notes (I had the cylinder numbers mostly written down), and perseverance with fdisk. I wrote experimental partition-tables untill I was able to mount them.
Just imagine my glee when hda3 fsck'd good !
So now, Im trying to recover hda4 now, with LVM volumes intact;
vgcfgrestore -l -l -v -d -n _vgb, reports 2 PVs, hdb2, hda4, both are
available, with some unusable, ( I cant cut-paste here, different
computer, cant boot clean without /var
pvscan however reports 2 different PVs, hdb2, and hdc9
Im guessing that I did a pvcreate /dev/hdc9 after some snapshot/backup, since hdc9 isnt there. This suggests that my chances of recovery are poorer than otherwize. I never actually did a vgcfgsave - Ive only been a couple of weeks with LVM, and it was only /tmp...
anyway, pvdata /dev/hda4 shows bogus (ie unfavorable, not wrong) data in the PV, it also segfaults, $? is 139
PV size 8 / Not usable 262 GB [LVM 3.71 GB]
PE Size(KB) 250
btw - 3.71 GB is reasonable, the hda4 has ~3.9 GB
$> pvdisplay /dev/hda4
-- no physical volume identifier
vgcfgrestore gives error when I try above:
ERROR: pv_read(): PV identifer invalid" reading physical volume
I should mention; I dont understand how sectors in hda4 got corrupted,
at least by my dd ( I did have bs=512 count=1, and hda[1-3] are ok).
Something else may be missing..
SO, WHAT IF ANY ARE MY OPTIONS ?
1) Would a carefully considered set of 'dd' commands possibly
restore it? I have nothing to lose in hda4 at this point.
2) IS IT POSSIBLE THAT DESPITE MY SUCCESS MOUNTING hda 1-3, particularly hda3, since thats ext2, (ie a real filesystem, with a real fsck). Ive somehow got the partitions wrong, and thus pvdata is looking in the wrong disk sector for its meta-data ?
3) is it possible to use fdisk to change partition type to Linux, then do an fsck ?
Im theorizing that fsck will find 3 different ext2 super-blocks somewhere within the previously mountable LVM partition ?
I think I can claim enough space elsewhere, and make a file-clone of the partition, if so, I can let fsck do all its repair attempts w/o trashing the possibility
of using approaches 1,2