OpenStack Swift Storage Calculator

Size a Swift object ring: raw capacity for the replica count, drive count, object count and partitions per drive.

About OpenStack Swift Storage Calculator

Swift stores each object once per replica across distinct failure domains, so raw capacity is logical data times the replica factor plus filesystem overhead. Partition power is the number that cannot be changed easily: the ring is fixed at 2^power partitions, and you pick it so that the largest cluster you ever plan to build still averages around 100 partition replicas per drive. Partition power is effectively a one-way decision — too low and data never balances across a grown cluster, too high and replicators and auditors spend all day walking directories — so it is worth calculating against your five-year drive count, not today's.

Formula

OpenStack Swift Storage

raw = logical data × replica factor × (1 + filesystem overhead); drives = raw ÷ (drive size × maximum utilisation); partition replicas per drive = 2^partition power × replicas ÷ drives.

replica factor: Raw bytes per logical byte — 3 for the default three-replica ring
partition power: Exponent fixing the ring at 2^power partitions, effectively permanent
partition replicas per drive: Placement granularity; roughly 100 is the target

Worked example

With the default values below, OpenStack Swift Storage Calculator returns Raw Capacity Required of 1 PiB. Change any input above and every figure here is recalculated in your browser.

Inputs used

Logical object dataaccepts 0.1–100,000 TB: 500 TB
Average object sizeaccepts 0.001–5,120 MiB: 4 MiB
Ring protectionone of 3 replicas (default), 2 replicas, Erasure coded 10+4 (1.4x raw), Erasure coded 8+4 (1.5x raw): 3 replicas (default)
Partition poweraccepts 8–24 bits: 16 bits
Size of each driveaccepts 0.1–100 TB: 18 TB
Filesystem and metadata overheadaccepts 0–30 %: 5 %
Maximum drive utilisationaccepts 30–95 %: 80 %

Results

Raw Capacity Required: 1 PiB
Drives Required: 110 drives
Objects Stored: 119,209,290 objects
Partitions in the Ring: 65,536 partitions
Partition Replicas per Drive: 1,787.3 per drive
Partition Power Verdict: Very high partition count per drive — replication and auditing overhead will be heavy

Step by step

1Values used
2OpenStack Swift Storage
3Raw Capacity Required= 1,575,000,000,000,000
4Drives Required= 110 drives
5Objects Stored= 119,209,290 objects
6Partitions in the Ring= 65,536 partitions
7Partition Replicas per Drive= 1,787.3 per drive
8Partition Power Verdict= Very high partition count per drive — replication and auditing overhead will be heavy

Assumptions and limits

The result is derived only from the 7 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

How is OpenStack Swift Storage calculated?

raw = logical data × replica factor × (1 + filesystem overhead); drives = raw ÷ (drive size × maximum utilisation); partition replicas per drive = 2^partition power × replicas ÷ drives. Swift stores each object once per replica across distinct failure domains, so raw capacity is logical data times the replica factor plus filesystem overhead. Partition power is the number that cannot be changed easily: the ring is fixed at 2^power partitions, and you pick it so that the largest cluster you ever plan to build still averages around 100 partition replicas per drive.

Why does OpenStack Swift Storage matter?

Partition power is effectively a one-way decision — too low and data never balances across a grown cluster, too high and replicators and auditors spend all day walking directories — so it is worth calculating against your five-year drive count, not today's.

What values do I need to enter?

This calculator takes 7 inputs: Logical object data, Average object size, Ring protection, Partition power, Size of each drive, Filesystem and metadata overhead, Maximum drive utilisation. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

Why does object count matter as well as capacity?

Swift keeps container database rows per object, so many small objects stress the container layer long before the drives fill. A ring holding a billion 4 KiB objects needs container sharding attention that a ring holding the same bytes as large objects does not.