[linux-lvm] vg disappeared after replacing disc in raid10
Björn Nadrowski
bjrnfrdnnd at gmail.com
Tue Mar 26 18:13:34 UTC 2013
On Mar 26, 2013, at 14:41 , Stuart D Gathman <stuart at bmsi.com> wrote:
> Long ago, Nostradamus foresaw that on 03/25/2013 05:45 PM, Björn
> Nadrowski would write:
>> You were right,
>> the data has been overwritten.
>> It now reads thus (or rather, the first instance of human-readable
>> volume group description reads thus; my old volume group description
>> is still there, but further down...):
> Now you are getting somewhere. The offset of your PV has shifted.
> First, copy that 2nd human readable part to removable media somewhere.
> If possible, backup your drives (e.g. to USB drives) so you can recover
> from further mistakes.
>
> Why has the offset shifted? Possibilities:
>
> 1) different md driver version on knoppix (although using an older
> version would move the md superblock from end of drive to beginning of
> drive - shifting the opposite way). Or different options. BUT mdadm
> seemed to recognize your RAID, so let's
> discount this theory.
>
> 2) alignment options to pvcreate - but it still should have been seen by
> lvs!
>
> 3) the offset hasn't shifted, but you've written over the first few
> sectors with the empty VG. Is the 2nd human readable part, by any
> chance, missing the first part? You could post both parts for us to
> look at.
>
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> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
Thanks for all these hints.
I can actually just restore the first bytes of the device as I saved the output of the original dd command to a file.
sudo dd if=/dev/md127 bs=512 count=255 skip=1 of=md0.txt
So I could just do
sudo dd if=md0.txt bs=512 count=255 skip=1 of=/dev/md127
Might this be the appropriate action?
I doubt that the entire array has shifted, as md0.txt contained two complete human-readable descriptions of my volume groups and my
logical volumes. This is the human-readable part of md0.txt (result of the dd command right after disc replacement):
------------------------------
vol0 {
id = "2daJft-nq2X-zJen-2VO1-c2Od-HREv-zyjKTz"
seqno = 7
status = ["RESIZEABLE", "READ", "WRITE"]
extent_size = 8192
max_lv = 0
max_pv = 0
physical_volumes {
pv0 {
id = "WFo1On-anFb-2av8-DuRq-vKee-nJEt-ZLnu26"
device = "/dev/md0"
status = ["ALLOCATABLE"]
dev_size = 5820316928
pe_start = 384
pe_count = 710487
}
}
logical_volumes {
root {
id = "iO0y32-L53R-msRI-3JiE-t7j1-Ija2-3SOnpC"
status = ["READ", "WRITE", "VISIBLE"]
segment_count = 1
segment1 {
start_extent = 0
extent_count = 11920
type = "striped"
stripe_count = 1 # linear
stripes = [
"pv0", 0
]
}
}
home {
id = "1Vk6QQ-c3NF-6z6h-zw7E-fkFU-mRWU-DKLM6t"
status = ["READ", "WRITE", "VISIBLE"]
segment_count = 1
segment1 {
start_extent = 0
extent_count = 674725
type = "striped"
stripe_count = 1 # linear
stripes = [
"pv0", 11920
]
}
}
}
}
# Generated by LVM2 version 2.02.39 (2008-06-27): Wed Jun 10 13:21:55 2009
contents = "Text Format Volume Group"
version = 1
description = ""
creation_host = "cn-b204-4" # Linux cn-b204-4 2.6.28-11-generic #42-Ubuntu SMP Fri Apr 17 01:58:03 UTC 2009 x86_64
creation_time = 1244640115 # Wed Jun 10 13:21:55 2009
vol0 {
id = "2daJft-nq2X-zJen-2VO1-c2Od-HREv-zyjKTz"
seqno = 8
status = ["RESIZEABLE", "READ", "WRITE"]
extent_size = 8192
max_lv = 0
max_pv = 0
physical_volumes {
pv0 {
id = "WFo1On-anFb-2av8-DuRq-vKee-nJEt-ZLnu26"
device = "/dev/md0"
status = ["ALLOCATABLE"]
dev_size = 5820316928
pe_start = 384
pe_count = 710487
}
}
logical_volumes {
root {
id = "iO0y32-L53R-msRI-3JiE-t7j1-Ija2-3SOnpC"
status = ["READ", "WRITE", "VISIBLE"]
segment_count = 1
segment1 {
start_extent = 0
extent_count = 11920
type = "striped"
stripe_count = 1 # linear
stripes = [
"pv0", 0
]
}
}
home {
id = "1Vk6QQ-c3NF-6z6h-zw7E-fkFU-mRWU-DKLM6t"
status = ["READ", "WRITE", "VISIBLE"]
segment_count = 1
segment1 {
start_extent = 0
extent_count = 674725
type = "striped"
stripe_count = 1 # linear
stripes = [
"pv0", 11920
]
}
}
empty {
id = "YToY9o-223w-nMrv-X5qU-0S8t-oUbG-Zk6ZmV"
status = ["READ", "WRITE", "VISIBLE"]
segment_count = 1
segment1 {
start_extent = 0
extent_count = 23842
type = "striped"
stripe_count = 1 # linear
stripes = [
"pv0", 686645
]
}
}
}
}
# Generated by LVM2 version 2.02.39 (2008-06-27): Wed Jun 10 13:22:04 2009
contents = "Text Format Volume Group"
version = 1
description = ""
creation_host = "cn-b204-4" # Linux cn-b204-4 2.6.28-11-generic #42-Ubuntu SMP Fri Apr 17 01:58:03 UTC 2009 x86_64
creation_time = 1244640124 # Wed Jun 10 13:22:04 2009
---------------------------
This is the human-readable part of the beginning of the device after my vgcreate action:
---------------------------
vol0 {
id = "8kEHPL-yDuF-7ffg-GeGH-dEg6-D0Qn-lUrKoh"
seqno = 1
format = "lvm2" # informational
status = ["RESIZEABLE", "READ", "WRITE"]
flags = []
extent_size = 8192
max_lv = 0
max_pv = 0
metadata_copies = 0
physical_volumes {
pv0 {
id = "WFo1On-anFb-2av8-DuRq-vKee-nJEt-ZLnu26"
device = "/dev/md127"
status = ["ALLOCATABLE"]
flags = []
dev_size = 5820316928
pe_start = 384
pe_count = 710487
}
}
}
# Generated by LVM2 version 2.02.95(2) (2012-03-06): Sun Mar 24 23:39:50 2013
contents = "Text Format Volume Group"
version = 1
description = ""
creation_host = "Microknoppix" # Linux Microknoppix 3.6.11 #12 SMP PREEMPT Thu Dec 20 04:04:10 CET 2012 i686
creation_time = 1364168390 # Sun Mar 24 23:39:50 2013
vol0 {
id = "2daJft-nq2X-zJen-2VO1-c2Od-HREv-zyjKTz"
seqno = 8
status = ["RESIZEABLE", "READ", "WRITE"]
extent_size = 8192
max_lv = 0
max_pv = 0
physical_volumes {
pv0 {
id = "WFo1On-anFb-2av8-DuRq-vKee-nJEt-ZLnu26"
device = "/dev/md0"
status = ["ALLOCATABLE"]
dev_size = 5820316928
pe_start = 384
pe_count = 710487
}
}
logical_volumes {
root {
id = "iO0y32-L53R-msRI-3JiE-t7j1-Ija2-3SOnpC"
status = ["READ", "WRITE", "VISIBLE"]
segment_count = 1
segment1 {
start_extent = 0
extent_count = 11920
type = "striped"
stripe_count = 1 # linear
stripes = [
"pv0", 0
]
}
}
home {
id = "1Vk6QQ-c3NF-6z6h-zw7E-fkFU-mRWU-DKLM6t"
status = ["READ", "WRITE", "VISIBLE"]
segment_count = 1
segment1 {
start_extent = 0
extent_count = 674725
type = "striped"
stripe_count = 1 # linear
stripes = [
"pv0", 11920
]
}
}
empty {
id = "YToY9o-223w-nMrv-X5qU-0S8t-oUbG-Zk6ZmV"
status = ["READ", "WRITE", "VISIBLE"]
segment_count = 1
segment1 {
start_extent = 0
extent_count = 23842
type = "striped"
stripe_count = 1 # linear
stripes = [
"pv0", 686645
]
}
}
}
}
# Generated by LVM2 version 2.02.39 (2008-06-27): Wed Jun 10 13:22:04 2009
contents = "Text Format Volume Group"
version = 1
description = ""
creation_host = "cn-b204-4" # Linux cn-b204-4 2.6.28-11-generic #42-Ubuntu SMP Fri Apr 17 01:58:03 UTC 2009 x86_64
creation_time = 1244640124 # Wed Jun 10 13:22:04 2009
---------------------------------
It seems, in both cases I have the description of the two last configurations of my volume group. The first one is the actual one.
Both are complete.
So, should I rewrite the beginning of the device with the dd command?
What then?
Thanks a lot for all your help!
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