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 Physical Volume.
Any single disk / LUN on system is identified as PV. It can be raw or formatted with file system. Raw PV is referred as /dev/rdsk/c0t0d1 (legacy) or /dev/rdisk/disk1 (agile) whereas formatted one is referred as /dev/dsk/c0t0d1 (legacy) or /dev/disk/disk1 (agile). Check PV name in below output as 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
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
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 – Legacy block device file
/dev/dsk/cxtxdxs2 – Legacy block device file, partition 2
/dev/rdisk/diskx – Persistent character device file
/dev/rdisk/diskx_p2 – Persistent character device file, partition 2
/dev/disk/diskx – Persistent block device file
/dev/disk/diskx_p2 – Persistent block device file, partition 2
PE is Physical Extent.
Its smallest chunk of PV which can be used as block under file system. PV is consist of number of PEs. We always use PV names while using LVM commands. In above example PE size is set to 32MB & total 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 above example vg00 is volume group made up of single PV & its sliced down to 8 LV (only one shown in above exmaple)
LV is 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 are smallest chunk of LV.
Below tables gives you 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 above table, as max PE size is 64MB and 66,535 PEs max per VG, one can create max of 64×66353=4TB of file system.