Scenario
I have old server installed on one hard drive, without hardware/software RAID and without LVM - summarizing without any protection for system files. I would like to protect this system from disk hardware damages. How? I want implement LVM volume, exactly mirror volume. Now I have one hard drive for system, I need a second hard drive. With two hard drive we can create mirrored LVM logical volume.
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| Convertion single disk to LVM mirrored volume. |
Of course I would like to do this migration in the most possible easy way and which not taking too long. All procedure which it I presented here I doing in the test installation system on virtual environment (KVM) using Debian distribution.
Main problem
The biggest problem in this migration process is the low capabilities between GRUB bootloader and LVM volumes format. Of course GRUB have "lvm" module and LVM developers work to LVM more compatible with GRUB, but today GRUB can't start from e.g. LVM raid1 volume, so we must use mirrored volume.
Our main goals is to creating replication system from standalone (single disk) system.
LVM migration procedure
So we have system installed on single disk 2GB and this installation using only one partition for all system points e.g. /home, /var.
root@host1:~# df -h
Filesystem Size Used Avail Use% Mounted on
rootfs 2.0G 593M 1.3G 31% /
udev 10M 0 10M 0% /dev
tmpfs 49M 180K 49M 1% /run
/dev/disk/by-uuid/993c1a89-40b6-456a-8478-d1c2915782fd 2.0G 593M 1.3G 31% /
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 97M 0 97M 0% /run/shm
root@host1:~# fdisk /dev/vda
Command (m for help): p
Disk /dev/vda: 2147 MB, 2147483648 bytes
244 heads, 47 sectors/track, 365 cylinders, total 4194304 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000b7ab3
Device Boot Start End Blocks Id System
/dev/vda1 * 2048 4192255 2095104 83 Linux
Command (m for help): q
In this particular examples we have 2GB partition, but we can create more or less capacity partition. Because I want continue to use old disk (vda) with new bigger disk (vdb has 3GB) in mirror, I can't create greater partition in vdb than has vda, because in vda can fit only <= 2GB mirror images (both images of mirror must by the same size). Furthermore LVM to create mirrored volume require small amount of free space.
So, for this reason we create smallest partitions that has vda < 2GB, exactly 1990MB.
root@host1:~# fdisk /dev/vdb
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0xbb09b322.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.
Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)
Command (m for help): p
Disk /dev/vdb: 3221 MB, 3221225472 bytes
16 heads, 63 sectors/track, 6241 cylinders, total 6291456 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xbb09b322
Device Boot Start End Blocks Id System
Command (m for help): n
Partition type:
p primary (0 primary, 0 extended, 4 free)
e extended
Select (default p): p
Partition number (1-4, default 1):
Using default value 1
First sector (2048-6291455, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-6291455, default 6291455): +1990M
Command (m for help): t
Selected partition 1
Hex code (type L to list codes): L
0 Empty 24 NEC DOS 81 Minix / old Lin bf Solaris
1 FAT12 27 Hidden NTFS Win 82 Linux swap / So c1 DRDOS/sec (FAT-
2 XENIX root 39 Plan 9 83 Linux c4 DRDOS/sec (FAT-
3 XENIX usr 3c PartitionMagic 84 OS/2 hidden C: c6 DRDOS/sec (FAT-
4 FAT16 <32M 40 Venix 80286 85 Linux extended c7 Syrinx
5 Extended 41 PPC PReP Boot 86 NTFS volume set da Non-FS data
6 FAT16 42 SFS 87 NTFS volume set db CP/M / CTOS / .
7 HPFS/NTFS/exFAT 4d QNX4.x 88 Linux plaintext de Dell Utility
8 AIX 4e QNX4.x 2nd part 8e Linux LVM df BootIt
9 AIX bootable 4f QNX4.x 3rd part 93 Amoeba e1 DOS access
a OS/2 Boot Manag 50 OnTrack DM 94 Amoeba BBT e3 DOS R/O
b W95 FAT32 51 OnTrack DM6 Aux 9f BSD/OS e4 SpeedStor
c W95 FAT32 (LBA) 52 CP/M a0 IBM Thinkpad hi eb BeOS fs
e W95 FAT16 (LBA) 53 OnTrack DM6 Aux a5 FreeBSD ee GPT
f W95 Ext'd (LBA) 54 OnTrackDM6 a6 OpenBSD ef EFI (FAT-12/16/
10 OPUS 55 EZ-Drive a7 NeXTSTEP f0 Linux/PA-RISC b
11 Hidden FAT12 56 Golden Bow a8 Darwin UFS f1 SpeedStor
12 Compaq diagnost 5c Priam Edisk a9 NetBSD f4 SpeedStor
14 Hidden FAT16 <3 61 SpeedStor ab Darwin boot f2 DOS secondary
16 Hidden FAT16 63 GNU HURD or Sys af HFS / HFS+ fb VMware VMFS
17 Hidden HPFS/NTF 64 Novell Netware b7 BSDI fs fc VMware VMKCORE
18 AST SmartSleep 65 Novell Netware b8 BSDI swap fd Linux raid auto
1b Hidden W95 FAT3 70 DiskSecure Mult bb Boot Wizard hid fe LANstep
1c Hidden W95 FAT3 75 PC/IX be Solaris boot ff BBT
1e Hidden W95 FAT1 80 Old Minix
Hex code (type L to list codes): 8e
Changed system type of partition 1 to 8e (Linux LVM)
Command (m for help): p
Disk /dev/vdb: 3221 MB, 3221225472 bytes
16 heads, 63 sectors/track, 6241 cylinders, total 6291456 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xbb09b322
Device Boot Start End Blocks Id System
/dev/vdb1 2048 4077567 2037760 8e Linux LVM
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
Now we can create a normal LVM volume, but before this first we must install LVM.
root@host1:~# aptitude install lvm2
root@host1:~# pvcreate /dev/vdb1
Writing physical volume data to disk "/dev/vdb1"
Physical volume "/dev/vdb1" successfully created
root@host1:~# vgcreate system /dev/vdb1
Volume group "system" successfully created
root@host1:~# lvcreate -n rootfs -L 1900MB system
Logical volume "rootfs" created
root@host1:~# lvs -a
LV VG Attr LSize Pool Origin Data% Move Log Copy% Convert
rootfs system -wi-a--- 1.86g
Now we got LVM volume and we can create the file system on this volume.
root@host1:~# mkfs.ext4 /dev/system/rootfs
In this point we have all we need to start copy system files to the new partition. But as you know you can't copy from the mounted system, so we must run server from another system. For this goal we use SystemRescueCd. SystemRescueCd has the advantage of it has built in LVM supports.
But before we start copy system files, first we do other things which minimize counts of server restart. Now we create the new GRUB menu entry which allows boot our system from vdb1 (VG system, LV rootfs). Please note that boot the bootloadrer installed in vda will boot system storage in vdb (LVM volume). We don't have there system yet, but first we creates this entry in GRUB menu.
root@host1:~# blkid /dev/system/rootfs
/dev/system/rootfs: UUID="7fa359c8-6bde-4ecd-835b-2f753fd16a49" TYPE="ext4"
root@host1:~# vim /boot/grub/grub.cfg
/dev/system/rootfs: UUID="7fa359c8-6bde-4ecd-835b-2f753fd16a49" TYPE="ext4"
root@host1:~# vim /boot/grub/grub.cfg
 |
| Add new menu entry to GRUB |
You must copy the first menu entry and changes the four things:
Of course this value depends of how you name your LVM groups nad volumes, in this cases it is 'system' and 'rootfs'. The last thing you need to do now is change the name of menu entry e.g. append " LVM".
- add load LVM module ('insmod lvm') before load DOS partition
- change 'set root' value to LVM style: 'system-rootfs'
- update UUID in command 'search' on '--set' parameter
- change is in 'linux' command, the 'root' parameter - also must write to LVM style: '/dev/mapper/system-rootfs'.
Of course this value depends of how you name your LVM groups nad volumes, in this cases it is 'system' and 'rootfs'. The last thing you need to do now is change the name of menu entry e.g. append " LVM".
Now we can back to the copy system files process.
First we must boot our server from CD/DVD and choose default boot options. SystemRescueCd automation scans available drive to LVM metadata, but I do this manually to show that system detect our VG.
Next step we mount both partitions vda1 and vdb1, and copy all system files from it to new LVM volume.
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| Run server from SystemRescueCd and work on LVM volume. |
After we copy system files to the new volume we can boot our system from it. So reboot Live system and this time select from menu options 'Run from first hard drive' then we see our new entry in GRUB menu.
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| Boot system from vdb using bootloader on vda. |
Now we boot our system from the new copy and you can see different root system file mount point.
root@host1:~# df -hT
Filesystem Type Size Used Avail Use% Mounted on
rootfs rootfs 1.9G 596M 1.2G 34% /
udev devtmpfs 10M 0 10M 0% /dev
tmpfs tmpfs 49M 188K 49M 1% /run
/dev/mapper/system-rootfs ext4 1.9G 596M 1.2G 34% /
tmpfs tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs tmpfs 97M 0 97M 0% /run/shm
root@host1:~# lvs -a -o +devices
LV VG Attr LSize Pool Origin Data% Move Log Copy% Convert Devices
rootfs system -wi-ao-- 1.86g /dev/vdb1(0)
LV VG Attr LSize Pool Origin Data% Move Log Copy% Convert Devices
rootfs system -wi-ao-- 1.86g /dev/vdb1(0)
To have a complete system on our new hard drive with LVM volume yet we miss only bootloader on this disk. So now we install GRUB on the new disk (vdb).
root@host1:~# grub-install /dev/vdb
/usr/sbin/grub-probe: error: no such disk.
Auto-detection of a filesystem of /dev/mapper/system-rootfs failed.
Try with --recheck.
If the problem persists please report this together with the output of "/usr/sbin/grub-probe --device-map="/boot/grub/device.map" --target=fs -v /boot/grub" to <bug-grub@gnu.org>
root@host1:~# grub-install --recheck /dev/vdb
Installation finished. No error reported.
I have done yet command 'update-grub' but this is not necessary, even unnecessary!
root@host1:~# update-grub
Generating grub.cfg ...
Found linux image: /boot/vmlinuz-3.2.0-4-amd64
Found initrd image: /boot/initrd.img-3.2.0-4-amd64
Found Debian GNU/Linux (7.4) on /dev/vda1
done
Ok, from this moment we have all completed system with bootloader in new disk, totally independent from original hard drive. In this moment we finished the migration process to LVM. Now we start new process - convert normal LVM volume to mirrored LVM volume.
But first, it is the good moment to check if all service in system work properly, in particular if this is a productions server. You can now reboot system from new disk and try boot them from new disk (vdb).
If all work properly on new disk, then you can go to the next step witch is destroy original disk - yes we need second disk to create LVM mirror volume. For this goal we delete existing data and partition on vda.
root@host1:~# fdisk /dev/vda
Command (m for help): p
Disk /dev/vda: 2147 MB, 2147483648 bytes
244 heads, 47 sectors/track, 365 cylinders, total 4194304 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000b7ab3
Device Boot Start End Blocks Id System
/dev/vda1 * 2048 4192255 2095104 83 Linux
Command (m for help): d
Selected partition 1
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
root@host1:~# fdisk /dev/vda
Command (m for help): p
Disk /dev/vda: 2147 MB, 2147483648 bytes
16 heads, 63 sectors/track, 4161 cylinders, total 4194304 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000b7ab3
Device Boot Start End Blocks Id System
Command (m for help): n
Partition type:
p primary (0 primary, 0 extended, 4 free)
e extended
Select (default p): p
Partition number (1-4, default 1):
Using default value 1
First sector (2048-4194303, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-4194303, default 4194303):
Using default value 4194303
Command (m for help): t
Selected partition 1
Hex code (type L to list codes): 8e
Changed system type of partition 1 to 8e (Linux LVM)
Command (m for help): p
Disk /dev/vda: 2147 MB, 2147483648 bytes
16 heads, 63 sectors/track, 4161 cylinders, total 4194304 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000b7ab3
Device Boot Start End Blocks Id System
/dev/vda1 2048 4194303 2096128 8e Linux LVM
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
Next we create identical LVM structure on vda like we have on vdb - first create the new PV, extend VG (system) for new PV (vda1) and last convert exist LV volume (rootfs) to the mirrored volume. LVM automatically use new free PV (vda1) from 'system' VG.
root@host1:~# pvcreate /dev/vda1
Writing physical volume data to disk "/dev/vda1"
Physical volume "/dev/vda1" successfully created
root@host1:~# vgextend system /dev/vda1
Volume group "system" successfully extended
root@host1:~# vgs -a -o +devices
VG #PV #LV #SN Attr VSize VFree Devices
system 2 1 0 wz--n- 3.94g 2.08g /dev/vdb1(0)
root@host1:~# pvs -a
PV VG Fmt Attr PSize PFree
/dev/root --- 0 0
/dev/vda1 system lvm2 a-- 2.00g 2.00g
/dev/vdb1 system lvm2 a-- 1.94g 88.00m
/dev/vdc --- 0 0
/dev/vdd --- 0 0
root@host1:~# lvconvert -m1 system/rootfs
system/rootfs: Converted: 0.6%
system/rootfs: Converted: 74.7%
system/rootfs: Converted: 100.0%
root@host1:~# lvs -a -o +devices
LV VG Attr LSize Pool Origin Data% Move Log Copy% Convert Devices
rootfs system mwi-aom- 1.86g rootfs_mlog 100.00 rootfs_mimage_0(0),rootfs_mimage_1(0)
[rootfs_mimage_0] system iwi-aom- 1.86g /dev/vdb1(0)
[rootfs_mimage_1] system iwi-aom- 1.86g /dev/vda1(0)
[rootfs_mlog] system lwi-aom- 4.00m /dev/vdb1(475)
In this moment we have the same data in two disk (vda1 and vdb1), to fully happy we miss only bootloader on vda.
root@host1:~# grub-install /dev/vda
Installation finished. No error reported.
Now we can reboot our system and boot it from original disk (vda).
root@host1:~# reboot
Broadcast message from root@host1 (pts/0) (Mon Oct 6 18:44:54 2014):
The system is going down for reboot NOW!
root@host1:~# Connection to 192.168.122.248 closed by remote host.
Connection to 192.168.122.248 closed.
grzesiek@probook:~$ ssh root@192.168.122.248
root@192.168.122.248's password:
Linux host1 3.2.0-4-amd64 #1 SMP Debian 3.2.54-2 x86_64
The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.
Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Mon Oct 6 18:34:20 2014 from 192.168.122.1
root@host1:~# df -hT
Filesystem Type Size Used Avail Use% Mounted on
rootfs rootfs 1.9G 596M 1.2G 34% /
udev devtmpfs 10M 0 10M 0% /dev
tmpfs tmpfs 49M 200K 49M 1% /run
/dev/mapper/system-rootfs ext4 1.9G 596M 1.2G 34% /
tmpfs tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs tmpfs 97M 0 97M 0% /run/shm
root@host1:~# lvs -a -o +devices
LV VG Attr LSize Pool Origin Data% Move Log Copy% Convert Devices
rootfs system mwi-aom- 1.86g rootfs_mlog 100.00 rootfs_mimage_0(0),rootfs_mimage_1(0)
[rootfs_mimage_0] system iwi-aom- 1.86g /dev/vdb1(0)
[rootfs_mimage_1] system iwi-aom- 1.86g /dev/vda1(0)
[rootfs_mlog] system lwi-aom- 4.00m /dev/vdb1(475)
root@host1:~# grub-install /dev/vdb
Installation finished. No error reported.
root@host1:~#
The last, what we must do, it is install GRUB on vdb, this operaions overwrite existing menu entry witch adds command 'update-grub'.
So now we have identical two disk with LVM mirrored volume. Also we have on each fo them installed bootloader so we can boot from any of them. When one of it is crashed we can boot server from SystemRescueCd and convert missing pair mirrored volume to normal LVM volume from one good disk, and we have our system.
Remember, each time you update kernel or GRUB you must also install GRUB on vdb to be able boot your system from vbd in future. I test this and is working properly :)
 |
| Boot from new disk. |
 |
| Bootloadre in new disk. |
If all work properly on new disk, then you can go to the next step witch is destroy original disk - yes we need second disk to create LVM mirror volume. For this goal we delete existing data and partition on vda.
root@host1:~# fdisk /dev/vda
Command (m for help): p
Disk /dev/vda: 2147 MB, 2147483648 bytes
244 heads, 47 sectors/track, 365 cylinders, total 4194304 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000b7ab3
Device Boot Start End Blocks Id System
/dev/vda1 * 2048 4192255 2095104 83 Linux
Command (m for help): d
Selected partition 1
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
root@host1:~# fdisk /dev/vda
Command (m for help): p
Disk /dev/vda: 2147 MB, 2147483648 bytes
16 heads, 63 sectors/track, 4161 cylinders, total 4194304 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000b7ab3
Device Boot Start End Blocks Id System
Command (m for help): n
Partition type:
p primary (0 primary, 0 extended, 4 free)
e extended
Select (default p): p
Partition number (1-4, default 1):
Using default value 1
First sector (2048-4194303, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-4194303, default 4194303):
Using default value 4194303
Command (m for help): t
Selected partition 1
Hex code (type L to list codes): 8e
Changed system type of partition 1 to 8e (Linux LVM)
Command (m for help): p
Disk /dev/vda: 2147 MB, 2147483648 bytes
16 heads, 63 sectors/track, 4161 cylinders, total 4194304 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000b7ab3
Device Boot Start End Blocks Id System
/dev/vda1 2048 4194303 2096128 8e Linux LVM
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
Next we create identical LVM structure on vda like we have on vdb - first create the new PV, extend VG (system) for new PV (vda1) and last convert exist LV volume (rootfs) to the mirrored volume. LVM automatically use new free PV (vda1) from 'system' VG.
root@host1:~# pvcreate /dev/vda1
Writing physical volume data to disk "/dev/vda1"
Physical volume "/dev/vda1" successfully created
root@host1:~# vgextend system /dev/vda1
Volume group "system" successfully extended
root@host1:~# vgs -a -o +devices
VG #PV #LV #SN Attr VSize VFree Devices
system 2 1 0 wz--n- 3.94g 2.08g /dev/vdb1(0)
root@host1:~# pvs -a
PV VG Fmt Attr PSize PFree
/dev/root --- 0 0
/dev/vda1 system lvm2 a-- 2.00g 2.00g
/dev/vdb1 system lvm2 a-- 1.94g 88.00m
/dev/vdc --- 0 0
/dev/vdd --- 0 0
root@host1:~# lvconvert -m1 system/rootfs
system/rootfs: Converted: 0.6%
system/rootfs: Converted: 74.7%
system/rootfs: Converted: 100.0%
root@host1:~# lvs -a -o +devices
LV VG Attr LSize Pool Origin Data% Move Log Copy% Convert Devices
rootfs system mwi-aom- 1.86g rootfs_mlog 100.00 rootfs_mimage_0(0),rootfs_mimage_1(0)
[rootfs_mimage_0] system iwi-aom- 1.86g /dev/vdb1(0)
[rootfs_mimage_1] system iwi-aom- 1.86g /dev/vda1(0)
[rootfs_mlog] system lwi-aom- 4.00m /dev/vdb1(475)
 |
| Synchronization two volume. |
root@host1:~# grub-install /dev/vda
Installation finished. No error reported.
Now we can reboot our system and boot it from original disk (vda).
root@host1:~# reboot
Broadcast message from root@host1 (pts/0) (Mon Oct 6 18:44:54 2014):
The system is going down for reboot NOW!
root@host1:~# Connection to 192.168.122.248 closed by remote host.
Connection to 192.168.122.248 closed.
grzesiek@probook:~$ ssh root@192.168.122.248
root@192.168.122.248's password:
Linux host1 3.2.0-4-amd64 #1 SMP Debian 3.2.54-2 x86_64
The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.
Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Mon Oct 6 18:34:20 2014 from 192.168.122.1
root@host1:~# df -hT
Filesystem Type Size Used Avail Use% Mounted on
rootfs rootfs 1.9G 596M 1.2G 34% /
udev devtmpfs 10M 0 10M 0% /dev
tmpfs tmpfs 49M 200K 49M 1% /run
/dev/mapper/system-rootfs ext4 1.9G 596M 1.2G 34% /
tmpfs tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs tmpfs 97M 0 97M 0% /run/shm
root@host1:~# lvs -a -o +devices
LV VG Attr LSize Pool Origin Data% Move Log Copy% Convert Devices
rootfs system mwi-aom- 1.86g rootfs_mlog 100.00 rootfs_mimage_0(0),rootfs_mimage_1(0)
[rootfs_mimage_0] system iwi-aom- 1.86g /dev/vdb1(0)
[rootfs_mimage_1] system iwi-aom- 1.86g /dev/vda1(0)
[rootfs_mlog] system lwi-aom- 4.00m /dev/vdb1(475)
root@host1:~# grub-install /dev/vdb
Installation finished. No error reported.
root@host1:~#
The last, what we must do, it is install GRUB on vdb, this operaions overwrite existing menu entry witch adds command 'update-grub'.
So now we have identical two disk with LVM mirrored volume. Also we have on each fo them installed bootloader so we can boot from any of them. When one of it is crashed we can boot server from SystemRescueCd and convert missing pair mirrored volume to normal LVM volume from one good disk, and we have our system.
Remember, each time you update kernel or GRUB you must also install GRUB on vdb to be able boot your system from vbd in future. I test this and is working properly :)