LVM2: device filter and LVM metadata restore

Customize LVM device filter to get rid of the annoying “/dev/cdrom: open failed” warning

##/dev/cdrom: open failed warning

$pvcreate /dev/sdb1

/dev/cdrom: open failed: Read-only file system

$ vgcreate vg01 /dev/sdb1

/dev/cdrom: open failed: Read-only file system

##The error because LVM scan all device files by default, you can exclude some device files by device filters

##File /etc/lvm/cache/.cache contains the device file names scanned by LVM

$ cat /etc/lvm/cache/.cache

persistent_filter_cache {

valid_devices=[

"/dev/ram11",

"/dev/cdrom",

##Edit /etc/lvm/lvm.conf, Change default filter  

filter = [ "a/.*/" ]

#to

filter = [ "r|/dev/cdrom|","r|/dev/ram*|" ]

##You need to delete the cache file or ran vgscan to regenerate the file

$rm /etc/lvm/cache/.cache   OR vgscan

LVM metadata backup and restore 
LVM record every LVM VG and LV metadata operation and save it to /etc/lvm/backup automatically, old version backup files are archived to /etc/lvm/archive.
The backup file can be used to rollback LVM metadata changes, for example, if you have removed the VG/PV or even re-initialize disk with pvcreate, Don’t panic,as long as file system was not re-created, you can use vgcfgrestore to restore all the data.
The following is to demonstrate how to recover a LV after it is completed destroyed from PV level (pvremove)
1.Create test LV and write some data

$pvcreate  /dev/sdb1 /dev/sdb2

Physical volume "/dev/sdb1" successfully created

Physical volume "/dev/sdb2" successfully created

$vgcreate vg01  /dev/sdb1 /dev/sdb2

Volume group "vg01" successfully created

$ lvcreate -L100M -n lv01 vg01

Logical volume "lv01" created

$ mkfs.ext3 /dev/vg01/lv01

$ mount /dev/vg01/lv01 /mnt/

$cp /etc/hosts /mnt/

$ ls /mnt/

hosts  lost+found

2.Destroy LV,VG,and PV

$vgremove vg01

Do you really want to remove volume group "vg01" containing 1 logical volumes? [y/n]: y

Do you really want to remove active logical volume lv01? [y/n]: y

Logical volume "lv01" successfully removed

Volume group "vg01" successfully removed

#VG is removed and PV was also wiped out

$ pvcreate /dev/sdb1 /dev/sdb2

Physical volume "/dev/sdb1" successfully created

Physical volume "/dev/sdb2" successfully created

3.Lets recover the LV and the data

##Find out the backup file to restore from

$vgcfgrestore -l vg01

..

file:         /etc/lvm/archive/vg01_00002.vg

VG name:      vg01

Description:  Created *before* executing 'vgremove vg01'

Backup time:  Tue May 10 15:41:31 2011

##first attempt failed, because PV UUID is changed

$ vgcfgrestore -f /etc/lvm/archive/vg01_00002.vg vg01

Couldn't find device with uuid 'pVf1J2-rAsd-eWkD-mCJc-S0pc-47zc-ImjXSB'.

Couldn't find device with uuid 'J14aVl-mbuj-k9MM-63Ad-TBAa-S0xF-VElV2W'.

Cannot restore Volume Group vg01 with 2 PVs marked as missing.

Restore failed.

##Find old UUID

$ grep -B 2 /dev/sdb /etc/lvm/archive/vg01_00002.vg

pv0 {

id = "pVf1J2-rAsd-eWkD-mCJc-S0pc-47zc-ImjXSB"

device = "/dev/sdb1"    # Hint only

--

pv1 {

id = "J14aVl-mbuj-k9MM-63Ad-TBAa-S0xF-VElV2W"

device = "/dev/sdb2"    # Hint only

$

##Recreate PV with the old UUID

$ pvcreate -u pVf1J2-rAsd-eWkD-mCJc-S0pc-47zc-ImjXSB /dev/sdb1

Physical volume "/dev/sdb1" successfully created

$ pvcreate -u J14aVl-mbuj-k9MM-63Ad-TBAa-S0xF-VElV2W  /dev/sdb2

Physical volume "/dev/sdb2" successfully created

##run vgcfgrestore again

$ vgcfgrestore -f /etc/lvm/archive/vg01_00002.vg vg01

Restored volume group vg01

##data was also recovered

$ mount /dev/vg01/lv01 /mnt/

mount: special device /dev/vg01/lv01 does not exist

$ lvchange -a y vg01/lv01

$ mount /dev/vg01/lv01 /mnt/

$ cat /mnt/hosts

127.0.0.1       localhost

..