1Heinz Mauelshagen's LVM (Logical Volume Manager) howto. 02/10/1999 2 3 4Abstract: 5--------- 6The LVM adds a kind of virtual disks and virtual partitions functionality 7to the Linux operating system. 8 9It achieves this by adding an additional layer between the physical peripherals 10and the i/o interface in the kernel. 11 12This allows the concatenation of several disk partitions or total disks 13(so-called physical volumes or PVs) or even multiple devices 14to form a storage pool (so-called Volume Group or VG) with 15allocation units called physical extents (called PE). 16You can think of the volume group as a virtual disk. 17Please see scenario below. 18 19Some or all PEs of this VG then can be allocated to so-called Logical Volumes 20or LVs in units called logical extents or LEs. 21Each LE is mapped to a corresponding PE. 22LEs and PEs are equal in size. 23Logical volumes are a kind of virtual partitions. 24 25 26The LVs can be used through device special files similar to the known 27/dev/sd[a-z]* or /dev/hd[a-z]* named /dev/VolumeGroupName/LogicalVolumeName. 28 29But going beyond this, you are able to extend or reduce 30VGs _AND_ LVs at runtime! 31 32So... 33If for example the capacity of a LV gets too small and your VG containing 34this LV is full, you could add another PV to that VG and simply extend 35the LV afterwards. 36If you reduce or delete a LV you can use the freed capacity for different 37LVs in the same VG. 38 39 40The above scenario looks like this: 41 42 /------------------------------------------\ 43 | /--PV2---\ VG 1 /--PVn---\ | 44 | |-VGDA---| |-VGDA-- | | 45 | |PE1PE2..| |PE1PE2..| | 46 | | | ...... | | | 47 | | | | | | 48 | | /-----------------------\ | | 49 | | \-------LV 1------------/ | | 50 | | ..PEn| | ..PEn| | 51 | \--------/ \--------/ | 52 \------------------------------------------/ 53 54PV 1 could be /dev/sdc1 sized 3GB 55PV n could be /dev/sde1 sized 4GB 56VG 1 could be test_vg 57LV 1 could be /dev/test_vg/test_lv 58VGDA is the volume group descriptor area holding the LVM metadata 59PE1 up to PEn is the number of physical extents on each disk(partition) 60 61 62 63Installation steps see INSTALL and insmod(1)/modprobe(1), kmod/kerneld(8) 64to load the logical volume manager module if you did not bind it 65into the kernel. 66 67 68Configuration steps for getting the above scenario: 69 701. Set the partition system id to 0x8e on /dev/sdc1 and /dev/sde1. 71 722. do a "pvcreate /dev/sd[ce]1" 73 For testing purposes you can use more than one partition on a disk. 74 You should not use more than one partition because in the case of 75 a striped LV you'll have a performance breakdown. 76 773. do a "vgcreate test_vg /dev/sd[ce]1" to create the new VG named "test_vg" 78 which has the total capacity of both partitions. 79 vgcreate activates (transfers the metadata into the LVM driver in the kernel) 80 the new volume group too to be able to create LVs in the next step. 81 824. do a "lvcreate -L1500 -ntest_lv test_vg" to get a 1500MB linear LV named 83 "test_lv" and it's block device special "/dev/test_vg/test_lv". 84 85 Or do a "lvcreate -i2 -I4 -l1500 -nanother_test_lv test_vg" to get a 100 LE 86 large logical volume with 2 stripes and stripesize 4 KB. 87 885. For example generate a filesystem in one LV with 89 "mke2fs /dev/test_vg/test_lv" and mount it. 90 916. extend /dev/test_vg/test_lv to 1600MB with relative size by 92 "lvextend -L+100 /dev/test_vg/test_lv" 93 or with absolute size by 94 "lvextend -L1600 /dev/test_vg/test_lv" 95 967. reduce /dev/test_vg/test_lv to 900 logical extents with relative extents by 97 "lvreduce -l-700 /dev/test_vg/test_lv" 98 or with absolute extents by 99 "lvreduce -l900 /dev/test_vg/test_lv" 100 1019. rename a VG by deactivating it with 102 "vgchange -an test_vg" # only VGs with _no_ open LVs can be deactivated! 103 "vgrename test_vg whatever" 104 and reactivate it again by 105 "vgchange -ay whatever" 106 1079. rename a LV after closing it by 108 "lvchange -an /dev/whatever/test_lv" # only closed LVs can be deactivated 109 "lvrename /dev/whatever/test_lv /dev/whatever/whatvolume" 110 or by 111 "lvrename whatever test_lv whatvolume" 112 and reactivate it again by 113 "lvchange -ay /dev/whatever/whatvolume" 114 11510. if you own Ted Tso's/Powerquest's resize2fs program, you are able to 116 resize the ext2 type filesystems contained in logical volumes without 117 destroyiing the data by 118 "e2fsadm -L+100 /dev/test_vg/another_test_lv" 119 120