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MinIO Storage Class Quickstart Guide Slack

MinIO server supports storage class in erasure coding mode. This allows configurable data and parity disks per object.

This page is intended as a summary of MinIO Erasure Coding. For a more complete explanation, see


MinIO supports two storage classes, Reduced Redundancy class and Standard class. These classes can be defined using environment variables set before starting MinIO server. After the data and parity disks for each storage class are defined using environment variables, you can set the storage class of an object via request metadata field x-amz-storage-class. MinIO server then honors the storage class by saving the object in specific number of data and parity disks.

Storage usage

The selection of varying data and parity drives has a direct impact on the drive space usage. With storage class, you can optimize for high redundancy or better drive space utilization.

To get an idea of how various combinations of data and parity drives affect the storage usage, let’s take an example of a 100 MiB file stored on 16 drive MinIO deployment. If you use eight data and eight parity drives, the file space usage will be approximately twice, i.e. 100 MiB file will take 200 MiB space. But, if you use ten data and six parity drives, same 100 MiB file takes around 160 MiB. If you use 14 data and two parity drives, 100 MiB file takes only approximately 114 MiB.

Below is a list of data/parity drives and corresponding approximate storage space usage on a 16 drive MinIO deployment. The field storage usage ratio is simply the drive space used by the file after erasure-encoding, divided by actual file size.

Total Drives (N) Data Drives (D) Parity Drives (P) Storage Usage Ratio
16 8 8 2.00
16 9 7 1.79
16 10 6 1.60
16 11 5 1.45
16 12 4 1.34
16 13 3 1.23
16 14 2 1.14

You can calculate approximate storage usage ratio using the formula - total drives (N) / data drives (D).

Allowed values for STANDARD storage class

STANDARD storage class implies more parity than REDUCED_REDUNDANCY class. So, STANDARD parity disks should be

  • Greater than or equal to 2, if REDUCED_REDUNDANCY parity is not set.
  • Greater than REDUCED_REDUNDANCY parity, if it is set.

Parity blocks can not be higher than data blocks, so STANDARD storage class parity can not be higher than N/2. (N being total number of disks)

The default value for the STANDARD storage class depends on the number of volumes in the erasure set:

Erasure Set Size Default Parity (EC:N)
5 or fewer EC:2
6-7 EC:3
8 or more EC:4

Prior to the RELEASE.2021-01-30T00-20-58Z MinIO release, the default STANDARD value was EC(N/2) where N was the number of erasure set drives. For more complete documentation on Erasure Set sizing, see the MinIO Documentation on Erasure Sets.

Allowed values for REDUCED_REDUNDANCY storage class

REDUCED_REDUNDANCY implies lesser parity than STANDARD class. So,REDUCED_REDUNDANCY parity disks should be

  • Less than N/2, if STANDARD parity is not set.
  • Less than STANDARD Parity, if it is set.

As parity below 2 is not recommended, REDUCED_REDUNDANCY storage class is not supported for 4 disks erasure coding setup.

Default value for REDUCED_REDUNDANCY storage class is 2.

Get started with Storage Class

Set storage class

The format to set storage class environment variables is as follows




Storage class can also be set via mc admin config get/set commands to update the configuration. Refer storage class for more details.


  • If STANDARD storage class is set via environment variables or mc admin config get/set commands, and x-amz-storage-class is not present in request metadata, MinIO server will apply STANDARD storage class to the object. This means the data and parity disks will be used as set in STANDARD storage class.

  • If storage class is not defined before starting MinIO server, and subsequent PutObject metadata field has x-amz-storage-class present with values REDUCED_REDUNDANCY or STANDARD, MinIO server uses default parity values.

Set metadata

In below example minio-go is used to set the storage class to REDUCED_REDUNDANCY. This means this object will be split across 6 data disks and 2 parity disks (as per the storage class set in previous step).

s3Client, err := minio.New("localhost:9000", "YOUR-ACCESSKEYID", "YOUR-SECRETACCESSKEY", true)
if err != nil {

object, err := os.Open("my-testfile")
if err != nil {
defer object.Close()
objectStat, err := object.Stat()
if err != nil {

n, err := s3Client.PutObject("my-bucketname", "my-objectname", object, objectStat.Size(), minio.PutObjectOptions{ContentType: "application/octet-stream", StorageClass: "REDUCED_REDUNDANCY"})
if err != nil {
log.Println("Uploaded", "my-objectname", " of size: ", n, "Successfully.")