Get acquainted with LVM (Logical Volume Manager) terms. Learn what is physical volume, logical volume, physical extent, volume group, and logical extent.
LVM (logical volume manager) legends
PV is a Physical Volume
Any single disk / LUN on the system is identified as PV. It can be raw or formatted with a file system. Raw PV is referred to as
/dev/rdsk/c0t0d1 (legacy) or
/dev/rdisk/disk1 (agile) whereas formatted one is referred to as
/dev/dsk/c0t0d1 (legacy) or
/dev/disk/disk1 (agile). Check PV name in below output as a formatted device.
# vgdisplay -v vg00 --- Volume groups --- VG Name /dev/vg00 VG Write Access read/write VG Status available Max LV 255 Cur LV 13 Open LV 13 Max PV 16 Cur PV 1 Act PV 1 Max PE per PV 4355 VGDA 2 PE Size (Mbytes) 32 Total PE 4345 Alloc PE 4303 Free PE 42 Total PVG 0 Total Spare PVs 0 Total Spare PVs in use 0 --- Logical volumes --- LV Name /dev/vg00/lvol1 LV Status available/syncd LV Size (Mbytes) 1024 Current LE 32 Allocated PE 32 Used PV 1 --- Physical volumes --- PV Name /dev/dsk/c3t0d0s2 PV Status available Total PE 4345 Free PE 42 Autoswitch On Proactive Polling On
Physical volume naming conventions :
/dev/rdsk/cxtxdx – Legacy character device file
/dev/rdsk/cxtxdxs2 – Legacy character device file, partition 2
/dev/dsk/cxtxdx – The legacy block device file
/dev/dsk/cxtxdxs2 – Legacy block device file, partition 2
/dev/rdisk/diskx – The persistent character device file
/dev/rdisk/diskx_p2 – Persistent character device file, partition 2
/dev/disk/diskx – The persistent block device file
/dev/disk/diskx_p2 – Persistent block device file, partition 2
PE is Physical Extent
Its smallest chunk of PV can be used as a block under the file system. PV is consists of the number of PEs. We always use PV names while using LVM commands. In the above example, PE size is set to 32MB & a total of 4345 PEs are available on disk.
Read our LVM tutorials: LVM cheat sheet.
VG is Volume Group
One or more PV come together to form a Volume Group. This grouping enables to slice down combined
storage capacity of disks to our choice of small volumes. In the above example, vg00 is volume group made up of single PV & it’s sliced down to 8 LV (only one shown in above example)
LV is the Logical Volume
Its a slice of volume group using some capacity of PV to form a smaller volume. Its basically used as a mount point /swap like drives (C:, D:) in Windows. We can see one LV in above example and its details.
LE is Logical Extent.
Same as PE, LE is the smallest chunk of LV.
Below tables gives you an idea about some numbers related to them:
LVs per VG range: 1-255, default: 255
PVs per VG range: 1-255, default: 16
PEs per VG range : 1-66535 default : 1016
with the above table, as max PE size is 64MB and 66,535 PEs max per VG, one can create a max of 64×66353=4TB of the file system.