Dear Andreas,
In message <20160516083903.GA29380@xxxxxxxxxxxxxxx> you wrote:
>
> First, you can use hexdump after all to have a look at the first chunk
> (assuming the 136KiB you found is actually the data offset).
>
> dd bs=136K skip=1 if=/dev/mapper/sda | hexdump -C | less
>
> (same for sd?)
>
> LVM metadata is in plaintext, example:
Well, this does not look so bad:
00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00000200 4c 41 42 45 4c 4f 4e 45 01 00 00 00 00 00 00 00 |LABELONE........|
00000210 3c fe 50 23 20 00 00 00 4c 56 4d 32 20 30 30 31 |<.P# ...LVM2 001|
00000220 34 79 78 49 78 69 48 73 6a 68 79 64 48 6f 76 58 |4yxIxiHsjhydHovX|
00000230 55 4f 30 48 47 31 5a 70 51 45 50 53 33 43 49 61 |UO0HG1ZpQEPS3CIa|
00000240 00 00 65 83 a3 03 00 00 00 00 03 00 00 00 00 00 |..e.............|
00000250 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000260 00 00 00 00 00 00 00 00 00 10 00 00 00 00 00 00 |................|
00000270 00 f0 02 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000280 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00001000 3a fe b8 5d 20 4c 56 4d 32 20 78 5b 35 41 25 72 |:..] LVM2 x[5A%r|
00001010 30 4e 2a 3e 01 00 00 00 00 10 00 00 00 00 00 00 |0N*>............|
00001020 00 f0 02 00 00 00 00 00 00 80 00 00 00 00 00 00 |................|
00001030 46 0b 00 00 00 00 00 00 65 8d d7 42 00 00 00 00 |F.......e..B....|
00001040 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00001200 63 61 73 74 6f 72 30 20 7b 0a 69 64 20 3d 20 22 |castor0 {.id = "|
00001210 56 33 52 6e 30 55 2d 47 4d 41 64 2d 34 55 73 4e |V3Rn0U-GMAd-4UsN|
00001220 2d 61 6d 35 69 2d 66 50 59 50 2d 41 43 37 70 2d |-am5i-fPYP-AC7p-|
00001230 66 4d 50 51 32 35 22 0a 73 65 71 6e 6f 20 3d 20 |fMPQ25".seqno = |
00001240 31 0a 73 74 61 74 75 73 20 3d 20 5b 22 52 45 53 |1.status = ["RES|
00001250 49 5a 45 41 42 4c 45 22 2c 20 22 52 45 41 44 22 |IZEABLE", "READ"|
00001260 2c 20 22 57 52 49 54 45 22 5d 0a 65 78 74 65 6e |, "WRITE"].exten|
00001270 74 5f 73 69 7a 65 20 3d 20 38 31 39 32 0a 6d 61 |t_size = 8192.ma|
00001280 78 5f 6c 76 20 3d 20 30 0a 6d 61 78 5f 70 76 20 |x_lv = 0.max_pv |
00001290 3d 20 30 0a 0a 70 68 79 73 69 63 61 6c 5f 76 6f |= 0..physical_vo|
000012a0 6c 75 6d 65 73 20 7b 0a 0a 70 76 30 20 7b 0a 69 |lumes {..pv0 {.i|
000012b0 64 20 3d 20 22 34 79 78 49 78 69 2d 48 73 6a 68 |d = "4yxIxi-Hsjh|
000012c0 2d 79 64 48 6f 2d 76 58 55 4f 2d 30 48 47 31 2d |-ydHo-vXUO-0HG1-|
000012d0 5a 70 51 45 2d 50 53 33 43 49 61 22 0a 64 65 76 |ZpQE-PS3CIa".dev|
000012e0 69 63 65 20 3d 20 22 2f 64 65 76 2f 6d 64 32 22 |ice = "/dev/md2"|
000012f0 0a 0a 73 74 61 74 75 73 20 3d 20 5b 22 41 4c 4c |..status = ["ALL|
00001300 4f 43 41 54 41 42 4c 45 22 5d 0a 64 65 76 5f 73 |OCATABLE"].dev_s|
00001310 69 7a 65 20 3d 20 37 38 31 34 30 39 39 35 38 34 |ize = 7814099584|
00001320 0a 70 65 5f 73 74 61 72 74 20 3d 20 33 38 34 0a |.pe_start = 384.|
00001330 70 65 5f 63 6f 75 6e 74 20 3d 20 39 35 33 38 36 |pe_count = 95386|
00001340 39 0a 7d 0a 7d 0a 0a 7d 0a 23 20 47 65 6e 65 72 |9.}.}..}.# Gener|
00001350 61 74 65 64 20 62 79 20 4c 56 4d 32 20 76 65 72 |ated by LVM2 ver|
00001360 73 69 6f 6e 20 32 2e 30 32 2e 33 39 20 28 32 30 |sion 2.02.39 (20|
00001370 30 38 2d 30 36 2d 32 37 29 3a 20 54 75 65 20 4a |08-06-27): Tue J|
00001380 61 6e 20 31 38 20 31 33 3a 30 31 3a 30 31 20 32 |an 18 13:01:01 2|
00001390 30 31 31 0a 0a 63 6f 6e 74 65 6e 74 73 20 3d 20 |011..contents = |
...
> For me this starts at offset 0x1200 (roughly 4K) should be well within
> your 16K chunk. It should look similar for you on one of your disks if
> the offset is correct.
Confirmed. So we can assume the offset if OK...
> You are using your disks in alphabetical order, are you sure this is
> the same order your RAID originally used? Maybe the drive letters
> changed?
I rechecked again...
> You found LABELONE on sda, which is your first drive (Device Role 0)
> in your RAID (see mdadm --examine after you create it), but when I
> create a new RAID based on loop devices, pvcreate and vgcreate it,
> the LABELONE actually appears on the 2nd drive (Device Role 1).
Confirmed. When I create a new array and pvcreate and vgcreate it, I
also see the LABELONE on /dev/mapper/sdb, at offset
134218240 LABELONE
= 131072 kB.
OK, so I started playing around with the disk order - even though I
checked yet another time from the disk serial numbers that the drive
order "a b c d e f" is what was used when initially creating the
array. When swapping the first two disks (so sda where the LABELONE
is present) becomes the second disk (i. e. "b a c d e f"), then LVM
will recognize the volume group and volumes, but data are corrupted.
So I guess I have to try the possible permutations (probably with sda
being the second disk only).
Doing that now. But I have no idea what could cause this...
Best regards,
Wolfgang Denk
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