## Overview

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 drives for each storage class are defined using environment variables,

By default, MinIO shards the objects across N/2 data and N/2 parity drives. Though, you can use [storage classes](https://github.com/minio/minio/tree/master/docs/erasure/storage-class) to use a custom configuration. We recommend N/2 data and parity blocks, as it ensures the best protection from drive failures.

		// Expected to send an empty response in this case.
		{"test-bucket-list-object", "", "zen", "", 10, ListObjectsInfo{}, nil, true},
		// Marker being set to a value which is lesser than and all object names when sorted (37).
		// Expected to send all the objects in the bucket in this case.
		{"test-bucket-list-object", "", "Abc", "", 10, resultCases[14], nil, true},

		{bucketNames[1], "", "minio-object-1.txt", uploadIDs[2], "", 100, listMultipartResults[17], nil, true},
		// Test cases with multiple uploadID listing for a given object (Test number 31-32).
		// MaxKeys set to values lesser than the number of entries in the MultipartInfo.
		// IsTruncated is expected to be true.
		{bucketNames[1], "", "", "", "", 2, listMultipartResults[18], nil, true},

			}
			// Data exists on disk, remove the version from metadata.
			fi.Data = nil
		}

		// Reading data for small objects when
		// - object has not yet transitioned
		// - object size lesser than 128KiB
		// - object has maximum of 1 parts
		if fi.TransitionStatus == "" &&
			fi.DataDir != "" && fi.Size <= smallFileThreshold &&
			len(fi.Parts) == 1 {

			return Config{}, err
		}
	} else {
		cfg.RRS.Parity = defaultRRSParity
		if setDriveCount == 1 {
			cfg.RRS.Parity = 0
		}
	}

	// Validation is done after parsing both the storage classes. This is needed because we need one
	// storage class value to deduce the correct value of the other storage class.
	if err = validateParity(cfg.Standard.Parity, cfg.RRS.Parity, setDriveCount); err != nil {
		return Config{}, err

	}

	meta[xhttp.AmzObjectTagging] = oi.UserTags
	meta[xhttp.AmzTagDirective] = "REPLACE"

	if sc == "" {
		sc = oi.StorageClass
	}
	// drop non standard storage classes for tiering from replication
	if sc != "" && (sc == storageclass.RRS || sc == storageclass.STANDARD) {
		meta[xhttp.AmzStorageClass] = sc
	}

	meta[xhttp.MinIOSourceETag] = oi.ETag

}

func errUnsupportedStorageClass(err error) *s3Error {
	return &s3Error{
		code:       "UnsupportedStorageClass",
		message:    "Encountered an invalid storage class. Only STANDARD, STANDARD_IA, and ONEZONE_IA storage classes are supported.",
		statusCode: 400,
		cause:      err,
	}

				// buffer than the data itself, but the results are in-fact valid. So we validate
				// this error condition specifically treating it as a good condition with valid
				// results. In this scenario return 'n' is always lesser than the input buffer.
				if err == io.ErrUnexpectedEOF {
					if !bytes.Equal(testCase.expectedBuf, buf[:n]) {

Refer to sizing guide for more understanding on default values chosen depending on your erasure stripe size [here](https://github.com/minio/minio/blob/master/docs/distributed/SIZING.md). Parity settings can be changed using [storage classes](https://github.com/minio/minio/tree/master/docs/erasure/storage-class).

### Consistency Guarantees