LVM LV Size Calculator
Calculate logical volume size allocation from available volume group extents.
About LVM LV Size Calculator
A Logical Volume's actual size is always a whole number of Physical Extents (lvcreate rounds a requested size up to the nearest PE), and it can only be created or extended if the Volume Group has that many extents free. This calculator converts a requested LV size into extents, rounds up to the true allocated size, and checks feasibility against the VG's available free extents — the same math lvextend uses when growing an existing LV.
Formula
LV size from extents
LV_size = extents × PE_size; can_extend = VG_free_extents ≥ requested_extents
- e
- extents allocated
- P
- PE size
- E_free
- VG free extents
Worked example
With the default values below, LVM LV Size Calculator returns Feasibility of Feasible — 25600 extents allocated, 24400 extents remain free in the VG.. Change any input above and every figure here is recalculated in your browser.
Inputs used
- VG Free Extents Availableminimum 0
- 50,000
- Physical Extent (PE) Size (MB)minimum 1
- 4
- Requested LV Size (GB)minimum 0
- 100
Results
- Feasibility
- Feasible — 25600 extents allocated, 24400 extents remain free in the VG.
- Actual LV Size After Rounding (GB)
- 100.0000
- Extents Required
- 25,600
- PE Rounding Waste (MB)
- 0.000
- VG Free Extents After Allocation
- 24,400
- VG Free Capacity After (GB)
- 95.313
Step by step
- 1Values used
- 2LV size from extents
- 3Feasibility= Feasible — 25600 extents allocated, 24400 extents remain free in the VG.
- 4Actual LV Size After Rounding (GB)= 100.0000
- 5Extents Required= 25,600
- 6PE Rounding Waste (MB)= 0.000
- 7VG Free Extents After Allocation= 24,400
- 8VG Free Capacity After (GB)= 95.31
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why is my LV slightly larger than what I requested?
lvcreate always allocates in whole Physical Extents, so a requested size that isn't an exact multiple of the PE size (commonly 4MB) gets rounded up to the next full extent — the difference is usually a few MB at most and is harmless.
What happens if I request more space than the VG has free?
lvcreate or lvextend will fail with an 'insufficient free space' error rather than partially allocating. You'd need to either request a smaller size, add another PV to the VG (vgextend), or free space by shrinking/removing another LV first.
Can an LV span multiple physical volumes?
Yes — by default LVM's linear mapping can allocate an LV's extents from any combination of PVs in the VG (contiguous per PV, but the LV as a whole can cross PV boundaries), which is how LVM lets a single logical volume exceed any one physical disk's size.