[linux-lvm] trying to restore data after Harddisk breakdown

[Kai Iskratsch <kai@stella.at>]

I had a lvm System which was made of 3 PVs the Harddisks hde (30 GB),hdf 
(80 GB) and hdg (120 GB). The first harddisk on which I created the vg  
was hdf, then I  created  3 LVs on it. Moved the existing data from hde 
the VG, added hde as a PV and expanded one of the LVs.  After some 
months I added hdg and resized all LVs. Some time later I moved a bit of 
free Space between the LVs but forgot to backup my configuration.
Not very much longer one of the harddisks hde had a complete breakdown, 
it couldn't be found by the bios anymore. Since I still had waranty on 
it I sent it in and got some time later a replacement disk.
In the meantime I was able to extract the data from the 2 LVs which 
didnt span on the defect disk by using LVM2 and using
""vgscan ; vgchange -a y -P"".

Im Using now kernel 2.4.20 and device-mapper + lvm checked out from cvs 
yesterday night.
(Compilation was not that easy,  i had to make some changes for 
device-mapper
 lib/ioctl/libdevmapper.c,v
479c479
<       char *outbuf = (char *) dmi + dmi->data_offset;
---
 >       char *outbuf = (char *) dmi + dmi->data_start;
536c536
<                                  dmt->dmi.v3->data_offset);
---
 >                                  dmt->dmi.v3->data_start);
671c671
<       dmi->data_offset = sizeof(struct dm_ioctl);
---
 >       dmi->data_start = sizeof(struct dm_ioctl);
which  i hope is correct since the struct dm_ioctrl had no member 
data_offst and reading the comments for this struct  suggested that  
data_start should be an offset

and in lvm2 I needed to include  the kernel Include files into the 
INCLUDE part of  the MAKEFILE)

Now I have the replacement disk which should be only one large segment 
in one of the LVs.  So I thought that it could maybe possible to get the 
lvm up again by exracting the actual configuration that is used by 
"vgscan ; vgchange -a y -P" and making a vgcfgbackup of it with lvm2 and 
edit the backup since it is humanreadable and  restore it to the new  
harddisk.

so I  tried to make a vgcfgbackup which worked with the -P option
and got somthing which seemed a bit irritating for me:

--------------------------------------------------------
# Generated by LVM2: Sun Apr 27 09:26:39 2003

contents = "Text Format Volume Group"
version = 1

description = "Created *after* executing './vgcfgbackup -P'"

creation_host = "fuckup"    # Linux fuckup 2.4.20 #1 SMP Sun Apr 27 
00:32:28 CEST 2003 i686
creation_time = 1051428399    # Sun Apr 27 09:26:39 2003

Data {
    id = "PUHFUx-71YI-m24t-7aZQ-J9ZM-PSrD-F10Y3t"
    seqno = 0
    status = ["RESIZEABLE", "PARTIAL", "READ"]
    system_id = "matin1023540844"
    extent_size = 8192        # 4 Megabytes
    max_lv = 255
    max_pv = 255

    physical_volumes {

        pv0 {
            id = "3yHeIp-kPYG-dqYk-3Qvz-czTC-m05v-Hs44sq"
            device = "/dev/hdg1"    # Hint only

            status = ["ALLOCATABLE"]
            pe_start = 8696
            pe_count = 29310    # 114.492 Gigabytes
        }

        pv1 {
            id = "834fZw-DSuv-0gGa-2313-Ud40-uqyh-mh3zbW"
            device = "/dev/hdf1"    # Hint only

            status = ["ALLOCATABLE"]
            pe_start = 8696
            pe_count = 19078    # 74.5234 Gigabytes
        }
    }

    logical_volumes {

        MP3 {
            id = "000000-0000-0000-0000-0000-0000-000000"
            status = ["READ", "WRITE", "VISIBLE"]
            allocation_policy = "next free"
            read_ahead = 120
            segment_count = 1

            segment1 {
                start_extent = 0
                extent_count = 12800    # 50 Gigabytes

                type = "striped"
                stripe_count = 1    # linear

                stripes = [
                    "pv0", 0
                ]
            }
        }

        DATA {
            id = "000000-0000-0000-0000-0000-0000-000001"
            status = ["READ", "WRITE", "VISIBLE"]
            allocation_policy = "next free"
            read_ahead = 120
            segment_count = 1

            segment1 {
                start_extent = 0
                extent_count = 5120    # 20 Gigabytes

                type = "striped"
                stripe_count = 1    # linear

                stripes = [
                    "pv0", 15360
                ]
            }
        }

        VIDEO {
            id = "000000-0000-0000-0000-0000-0000-000002"
            status = ["READ", "WRITE", "VISIBLE"]
            allocation_policy = "next free"
            read_ahead = 120
            segment_count = 7328

            segment1 {
                start_extent = 0
                extent_count = 8830    # 34.4922 Gigabytes

                type = "striped"
                stripe_count = 1    # linear

                stripes = [
                    "pv0", 20480
                ]
            }
            segment2 {
                start_extent = 8830
                extent_count = 1    # 4 Megabytes

                type = "striped"
                stripe_count = 1    # linear

                stripes = [
                    "Missing", 0
                ]
            }
....  (many more Missing Segments)
            segment7326 {
                start_extent = 16154
                extent_count = 1    # 4 Megabytes

                type = "striped"
                stripe_count = 1    # linear

                stripes = [
                    "Missing", 0
                ]
            }
            segment7327 {
                start_extent = 16155
                extent_count = 19078    # 74.5234 Gigabytes

                type = "striped"
                stripe_count = 1    # linear

                stripes = [
                    "pv1", 0
                ]
            }
            segment7328 {
                start_extent = 35233
                extent_count = 2560    # 10 Gigabytes

                type = "striped"
                stripe_count = 1    # linear

                stripes = [
                    "pv0", 12800
                ]
            }
        }
    }
}
-----------------------------------------------

first this says that the 120GB disk is my PV0 and the 80 GB is my PV1, 
second it says that my 2 working LVs are entirely on the 120 GB 
Harddisk, but I created them before on the 80 GB Disk so I thought they 
would be spanning  over both discs.

Is this backup wrong, then how do I get the data that  the system uses 
when I mount the two working LVs readonly?
Or has lvm moved the LVs on one of my resizes so that this data is 
correct and I only need to add the new PV and  replace all the Missing 
Segments by one on the new PV?

best regards

Kai Iskratsch