| Most people associate exporting and importing volume groups with the process of sharing volume groups between machines (a common task in a high-availability Serviceguard cluster). However, it is a good policy to keep a mapfile representing the configuration of each of your volume groups. In the event that you have to reinstall the operating system, your new OS disk will know nothing of the LVM structures on your data disks. With the mapfile (s), you will be able to import the LVM structures stored on your data disks, recreating the volume groups as they were configured before you had to reinstall the operating system. Let's look at an example of creating the mapfile :
root@hpeos003[] vgexport -m /etc/lvmconf/vgora1.map -p /dev/vgora1 vgexport: Volume group "/dev/vgora1" is still active. root@hpeos003[] cat /etc/lvmconf/vgora1.map 1 db 2 stripy 3 Dstripe 4 Kstripe root@hpeos003[] root@hpeos003[] strings /etc/lvmtab /dev/vg00 /dev/dsk/c1t15d0 /dev/dsk/c3t15d0 /dev/vgora1 /dev/dsk/c0t1d0 /dev/dsk/c0t2d0 /dev/dsk/c0t3d0 /dev/dsk/c4t9d0 /dev/dsk/c4t10d0 /dev/dsk/c5t1d0 /dev/dsk/c5t2d0 /dev/dsk/c5t3d0 /dev/dsk/c4t11d0 root@hpeos003[]
When we want to create a mapfile for our volume group, we use the preview option (-p ) to vgexport . This does not remove the volume group from the /etc/lvmtab files. As you can see, the content of the mapfile is simple ”a number followed by a name . In this way, when we import the volume group, LVM knows which extents belong to which logical volume. In the VGRA is an extent map for that particular disk. Marked against an individual extent is the logical volume number to which it belongs. In this way, when vgimport recreates the device files under the /dev/vgX directory, it knows (1) how many device files to create and (2) what to call those device files. Without a mapfile, vgimport would simply call the device files (and hence the logical volumes ), lvol1 , lvol2 , lvol3 , etc. This is not catastrophic, but it does mean that we have a bit more investigating to do to work out which logical volume contains which information. Here I will actually remove the volume group from this system. (Notice that there is no entry in /etc/lvmtab , and all device files pertaining to the volume group have been deleted.) For vgexport to work, no filesystems, swap, or dump devices can be open , and the volume group must be deactivated:
root@hpeos003[] vgchange -a n /dev/vgora1 Volume group "/dev/vgora1" has been successfully changed. root@hpeos003[] vgexport -m /etc/lvmconf/vgora1.map -s /dev/vgora1 Physical volume "/dev/dsk/c0t1d0" has been successfully deleted from physical volume group "PVG0". Physical volume "/dev/dsk/c0t2d0" has been successfully deleted from physical volume group "PVG0". Physical volume "/dev/dsk/c0t3d0" has been successfully deleted from physical volume group "PVG0". Physical volume "/dev/dsk/c4t9d0" has been successfully deleted from physical volume group "PVG1". Physical volume "/dev/dsk/c4t10d0" has been successfully deleted from physical volume group "PVG1". Physical volume "/dev/dsk/c4t11d0" has been successfully deleted from physical volume group "PVG1". root@hpeos003[] root@hpeos003[] strings /etc/lvmtab /dev/vg00 /dev/dsk/c1t15d0 /dev/dsk/c3t15d0 root@hpeos003[] ll /dev/vgora1 /dev/vgora1 not found root@hpeos003[] root@hpeos003[] cat /etc/lvmconf/vgora1.map VGID 355803d93f9fb09a 1 db 2 stripy 3 Dstripe 4 Kstripe root@hpeos003[]
Notice that I have used the “s option on the vgexport command this time. This has stored the VGID of the volume group in the mapfile . This may be useful later when we import the volume group. I will now import the volume group. In this instance, I will call the volume group the same name, although this is technically not necessary.
root@hpeos003[] mkdir /dev/vgora1 root@hpeos003[] mknod /dev/vgora1/group c 64 0x010000 root@hpeos003[] root@hpeos003[] vgimport -m /etc/lvmconf/vgora1.map -s /dev/vgora1 root@hpeos003[] root@hpeos003[] strings /etc/lvmtab /dev/vg00 /dev/dsk/c1t15d0 /dev/dsk/c3t15d0 /dev/vgora1 /dev/dsk/c0t1d0 /dev/dsk/c0t2d0 /dev/dsk/c0t3d0 /dev/dsk/c4t9d0 /dev/dsk/c4t10d0 /dev/dsk/c4t11d0 /dev/dsk/c5t1d0 /dev/dsk/c5t2d0 /dev/dsk/c5t3d0 root@hpeos003[] root@hpeos003[] ll /dev/vgora1 total 0 brw-r----- 1 root sys 64 0x010003 Oct 30 19:12 Dstripe brw-r----- 1 root sys 64 0x010004 Oct 30 19:12 Kstripe brw-r----- 1 root sys 64 0x010001 Oct 30 19:12 db crw-rw-r-- 1 root sys 64 0x010000 Oct 30 19:11 group crw-r----- 1 root sys 64 0x010003 Oct 30 19:12 rDstripe crw-r----- 1 root sys 64 0x010004 Oct 30 19:12 rKstripe crw-r----- 1 root sys 64 0x010001 Oct 30 19:12 rdb crw-r----- 1 root sys 64 0x010002 Oct 30 19:12 rstripy brw-r----- 1 root sys 64 0x010002 Oct 30 19:12 stripy root@hpeos003[] root@hpeos003[] vgchange -a y /dev/vgora1 Activated volume group Volume group "/dev/vgora1" has been successfully changed. root@hpeos003[] vgcfgbackup /dev/vgora1 Volume Group configuration for /dev/vgora1 has been saved in /etc/lvmconf/vgora1.conf root@hpeos003[]
Notice that I used the “s option with the vgimport command. This is the scan option. When we exported the volume group, the “s option stored the VGID in the mapfile . When we imported the volume group, vgimport scanned every disk on the system for any disk that reported it had the same VGID as stored in the mapfile . This scan option sounds like a fantastic idea. In reality, if you have a large number of disks ( especially Fibre Channel disks), then the scan option can take a considerable amount of time to complete. If you decide not to use it, then you will need to list all of the disks belonging to the volume group on the command line.
root@hpeos003[] vgimport -m /etc/lvmconf/vgora1.map /dev/vgora1 /dev/dsk/c0t1d0 /dev/dsk  /c0t2d0 /dev/dsk/c0t3d0 /dev/dsk/c4t9d0 /dev/dsk/c4t10d0 /dev/dsk/c4t11d0 /dev/dsk5t1d0 /dev/dsk/c5t2d0 /dev/dsk/c5t3d0 vgimport: Warning: Volume Group contains "6" PVs, "9" specified. Continuing. Warning: A backup of this volume group may not exist on this machine. Please remember to take a backup using the vgcfgbackup command after activating the volume group. root@hpeos003[] root@hpeos003[] strings /etc/lvmtab /dev/vg00 /dev/dsk/c1t15d0 /dev/dsk/c3t15d0 /dev/vgora1 /dev/dsk/c0t1d0 /dev/dsk/c0t2d0 /dev/dsk/c0t3d0 /dev/dsk/c4t9d0 /dev/dsk/c4t10d0 /dev/dsk/c4t11d0 /dev/dsk/c5t1d0 /dev/dsk/c5t2d0 /dev/dsk/c5t3d0 root@hpeos003[] root@hpeos003[] vgchange -a y /dev/vgora1 Activated volume group Volume group "/dev/vgora1" has been successfully changed. root@hpeos003[] vgcfgbackup /dev/vgora1 Volume Group configuration for /dev/vgora1 has been saved in /etc/lvmconf/vgora1.conf root@hpeos003[]
As you can see, the Warning is simply a warning; vgimport has identified the Alternate PV Links. I have seen in some instances that the vgimport does not accept all of the Alternate PV Link disks listed on the command line. In such circumstances, you may have to add them to the volume group with vgextend :
root@hpeos003[] vgdisplay -v vgora1 --- Volume groups --- VG Name /dev/vgora1 VG Write Access read/write VG Status available Max LV 255 Cur LV 4 Open LV 4 Max PV 16 Cur PV 6 Act PV 6 Max PE per PV 17501 VGDA 12 PE Size (Mbytes) 4 Total PE 104994 Alloc PE 1700 Free PE 103294 Total PVG 0 Total Spare PVs 0 Total Spare PVs in use 0 --- Logical volumes --- LV Name /dev/vgora1/db LV Status available/syncd LV Size (Mbytes) 1000 Current LE 250 Allocated PE 500 Used PV 2 LV Name /dev/vgora1/stripy LV Status available/syncd LV Size (Mbytes) 1200 Current LE 300 Allocated PE 300 Used PV 3 LV Name /dev/vgora1/Dstripe LV Status available/syncd LV Size (Mbytes) 1200 Current LE 300 Allocated PE 600 Used PV 6 LV Name /dev/vgora1/Kstripe LV Status available/syncd LV Size (Mbytes) 1200 Current LE 300 Allocated PE 300 Used PV 3 --- Physical volumes --- PV Name /dev/dsk/c0t1d0 PV Name /dev/dsk/c5t1d0 Alternate Link PV Status available Total PE 17499 Free PE 16949 Autoswitch On PV Name /dev/dsk/c0t2d0 PV Name /dev/dsk/c5t2d0 Alternate Link PV Status available Total PE 17499 Free PE 17199 Autoswitch On PV Name /dev/dsk/c0t3d0 PV Name /dev/dsk/c5t3d0 Alternate Link PV Status available Total PE 17499 Free PE 17199 Autoswitch On PV Name /dev/dsk/c4t9d0 PV Status available Total PE 17499 Free PE 17149 Autoswitch On PV Name /dev/dsk/c4t10d0 PV Status available Total PE 17499 Free PE 17399 Autoswitch On PV Name /dev/dsk/c4t11d0 PV Status available Total PE 17499 Free PE 17399 Autoswitch On root@hpeos003[]
Assuming that this was a reinstalled/new system, I would simply restore the mapfile , recreate my group file, and then vgimport the volume group. If you have misplaced your mapfile and you have to import the volume group without a mapfile , you will end up with logical volumes called lvol1 , lvol2 , lvol3 , and so on:
root@hpeos003[vgora1] pwd /dev/vgora1 root@hpeos003[vgora1] ll total 0 crw-rw-r-- 1 root sys 64 0x010000 Oct 30 19:23 group brw-r----- 1 root sys 64 0x010001 Oct 30 19:23 lvol1 brw-r----- 1 root sys 64 0x010002 Oct 30 19:23 lvol2 brw-r----- 1 root sys 64 0x010003 Oct 30 19:23 lvol3 brw-r----- 1 root sys 64 0x010004 Oct 30 19:23 lvol4 crw-r----- 1 root sys 64 0x010001 Oct 30 19:23 rlvol1 crw-r----- 1 root sys 64 0x010002 Oct 30 19:23 rlvol2 crw-r----- 1 root sys 64 0x010003 Oct 30 19:23 rlvol3 crw-r----- 1 root sys 64 0x010004 Oct 30 19:23 rlvol4 root@hpeos003[vgora1] root@hpeos003[vgora1] lvdisplay /dev/vgora1/lvol1 --- Logical volumes --- LV Name /dev/vgora1/lvol1 VG Name /dev/vgora1 LV Permission read/write LV Status available/syncd Mirror copies 1 Consistency Recovery MWC Schedule parallel LV Size (Mbytes) 1000 Current LE 250 Allocated PE 500 Stripes 0 Stripe Size (Kbytes) 0 Bad block on Allocation strict IO Timeout (Seconds) default root@hpeos003[vgora1]
If you later realize what your logical volumes should be called, the simplest way to rename a logical volume is to rename the device files:
root@hpeos003[vgora1] mv lvol1 db root@hpeos003[vgora1] mv rlvol1 rdb root@hpeos003[vgora1] mv lvol2 stripy root@hpeos003[vgora1] mv rlvol2 rstripy root@hpeos003[vgora1] mv lvol3 Dstripe root@hpeos003[vgora1] mv rlvol3 rDstripe root@hpeos003[vgora1] mv lvol4 Kstripe root@hpeos003[vgora1] mv rlvol4 rKstripe root@hpeos003[vgora1] root@hpeos003[vgora1] lvdisplay /dev/vgora1/db --- Logical volumes --- LV Name /dev/vgora1/db VG Name /dev/vgora1 LV Permission read/write LV Status available/syncd Mirror copies 1 Consistency Recovery MWC Schedule parallel LV Size (Mbytes) 1000 Current LE 250 Allocated PE 500 Stripes 0 Stripe Size (Kbytes) 0 Bad block on Allocation strict IO Timeout (Seconds) default root@hpeos003[vgora1]
This makes sense, because the minor number is simply a key into the extent map stored in the VGRA indicating which extents belong to which logical volume. | 