LVM Sizing Calculator

Work out lvm sizing instantly with clear inputs, formula shown and shareable results.

About LVM Sizing Calculator

A volume group is the sum of its physical volumes, divided into fixed-size physical extents — 4 MB by default, which caps a single logical volume's size in older LVM versions. The important discipline is not allocating the entire group: keeping 20 percent free leaves room for snapshots, which need space to hold changed blocks, and for growing volumes under pressure.

Formula

LVM capacity

VG size = PV size x PV count; extents = VG MB / extent size; allocatable = VG x (1 - snapshot reserve)

Worked example

With the default values below, LVM Sizing Calculator returns Volume group capacity of 4,000.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Physical volume sizeminimum 0.001 GB: 1,000 GB
Number of physical volumesminimum 1: 4
Physical extent sizeaccepts 1–512 MB: 4 MB
Reserve kept free for snapshotsaccepts 0–90 %: 20 %

Results

Volume group capacity: 4,000.0 GB
Capacity to allocate to logical volumes: 3,200.0 GB
Physical extents in the group: 1,000,000
Reserved for snapshots and growth: 800.0 GB

Step by step

1Values used
2LVM capacity
3Volume group capacity= 4,000.0 GB
4Capacity to allocate to logical volumes= 3,200.0 GB
5Physical extents in the group= 1,000,000
6Reserved for snapshots and growth= 800.0 GB

Assumptions and limits

The result is derived only from the 4 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 1 decimal place, 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 not allocate the whole volume group?

Because snapshots need unallocated space, and growing a filesystem under pressure requires free extents. Thin provisioning helps but still needs a backing pool with headroom.

Does extent size matter?

It sets the allocation granularity and historically limited maximum volume size. Larger extents suit very large volumes; the 4 MB default is fine up to many terabytes on modern LVM.