Recently I've had to backup/restore data from a failing drive with LVM over Raid.
Luckily I had access to the backup of the current metadata configuration located in "/etc/lvm/backup/".
Below is what the volumegroup looked like:
vg0 {
id = "xvni1W-24Xu-dVoR-PlXh-gQvQ-62fL-QX64O3"
seqno = 9
status = ["RESIZEABLE", "READ", "WRITE"]
flags = []
extent_size = 65536 # 32 Megabytes
max_lv = 0
max_pv = 0
physical_volumes {
pv0 {
id = "9gbyhX-Owvj-u4Q4-wR1E-IEf2-gyUA-CJBCJK"
device = "/dev/md3" # Hint only
status = ["ALLOCATABLE"]
flags = []
dev_size = 1928892288 # 919.768 Gigabytes
pe_start = 384
pe_count = 29432 # 919.75 Gigabytes
}
}
logical_volumes {
lv0_sites {
id = "Sg1fYr-NTzr-8AA2-v29K-tcz5-rUMj-uRoXY1"
status = ["READ", "WRITE", "VISIBLE"]
flags = []
segment_count = 1
segment1 {
start_extent = 0
extent_count = 1280 # 40 Gigabytes
type = "striped"
stripe_count = 1 # linear
stripes = [
"pv0", 0
]
}
}
lv0_m {
id = "scNeN4-4bmg-Y6kq-zKuO-n8B8-s8mw-FTUYqk"
status = ["READ", "WRITE", "VISIBLE"]
flags = []
segment_count = 1
segment1 {
start_extent = 0
extent_count = 12800 # 400 Gigabytes
type = "striped"
stripe_count = 1 # linear
stripes = [
"pv0", 1280
]
}
}
}
}Now to extract data with dd, use the below formula (this will only work for linear stripe):
skip=$[extent_size*stripes+pe_start] count=$[extent_size*(extent_count-1)]So to get the lv0_m data off of the volume:
dd if=/dev/sdb4 of=/opt/bak/lv0_m.iso bs=512 skip=$[65536*1280+384] count=$[65536*(12800-1)] conv=sync,noerrorOnce the iso is created, it can then be loop mounted via:
mount -o loop -t ext3 /opt/bak/lv0_m.iso /mnt/lv0_mYou should then be able to see all the files in the mount point which can then be used for data restoration.
