### Allowed values for STANDARD storage class

`STANDARD` storage class implies more parity than `REDUCED_REDUNDANCY` class. So, `STANDARD` parity drives 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 drives)

func ValidateParity(ssParity, setDriveCount int) error {
	// SS parity drives should be greater than or equal to minParityDrives.
	// Parity below minParityDrives is not supported.
	if ssParity > 0 && ssParity < minParityDrives {
		return fmt.Errorf("parity %d should be greater than or equal to %d",
			ssParity, minParityDrives)
	}

	if ssParity > setDriveCount/2 {

# Erasure code sizing guide

## Toy Setups

Capacity constrained environments, MinIO will work but not recommended for production.

| servers | drives (per node) | stripe_size | parity chosen (default) | tolerance for reads (servers) | tolerance for writes (servers) |
|--------:|------------------:|------------:|------------------------:|------------------------------:|-------------------------------:|

			Standard: StorageClass{
				Parity: 8,
			},
			RRS: StorageClass{
				Parity: 2,
			},
			initialized: true,
		}
		// Set env var for test case 4
		if i+1 == 4 {
			scfg.RRS.Parity = 7
		}
		// Set env var for test case 5
		if i+1 == 5 {
			scfg.Standard.Parity = 6
		}
		// Set env var for test case 6
		if i+1 == 6 {
			scfg.Standard.Parity = 7
		}

	}

	Help = config.HelpKVS{
		config.HelpKV{
			Key:         ClassStandard,
			Description: `set the parity count for default standard storage class` + defaultHelpPostfix(ClassStandard),
			Optional:    true,
			Type:        "string",
		},
		config.HelpKV{
			Key:         ClassRRS,
			Description: `set the parity count for reduced redundancy storage class` + defaultHelpPostfix(ClassRRS),
			Optional:    true,

)

var (
	configRRSParityMD = NewGaugeMD(configRRSParity,
		"Reduced redundancy storage class parity")
	configStandardParityMD = NewGaugeMD(configStandardParity,
		"Standard storage class parity")
)

// loadClusterConfigMetrics - `MetricsLoaderFn` for cluster config
// such as standard and RRS parity.
func loadClusterConfigMetrics(ctx context.Context, m MetricValues, c *metricsCache) error {

	for _, disk := range diskInfo {
		// Ignore invalid.
		if disk.PoolIndex < 0 || len(s.Backend.StandardSCData) <= disk.PoolIndex {
			// https://github.com/minio/minio/issues/16500
			continue
		}
		// Ignore parity disks
		if disk.DiskIndex < s.Backend.StandardSCData[disk.PoolIndex] {
			capacity += disk.TotalSpace
		}
	}
	return
}

// GetTotalCapacityFree gets the total capacity free in the cluster.

reconstruct missing or corrupted data. MinIO uses Reed-Solomon code to shard objects into variable data and parity blocks. For example, in a 12 drive setup, an object can be sharded to a variable number of data and parity blocks across all the drives - ranging from six data and six parity blocks to ten data and two parity blocks.

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)...

		version == xlMetaVersion100) &&
		format == xlMetaFormat)
}

// Verifies if the backend format metadata is sane by validating
// the ErasureInfo, i.e. data and parity blocks.
func isXLMetaErasureInfoValid(data, parity int) bool {
	return ((data >= parity) && (data > 0) && (parity >= 0))
}

//go:generate msgp -file=$GOFILE -unexported

// A xlMetaV1Object represents `xl.meta` metadata header.
type xlMetaV1Object struct {

	occMap := make(map[int]int)
	for _, p := range parities {
		occMap[p]++
	}

	var maxOcc, cparity int
	for parity, occ := range occMap {
		if parity == -1 {
			// Ignore non defined parity
			continue
		}

		readQuorum := N - parity
		if defaultParityCount > 0 && parity == 0 {
			// In this case, parity == 0 implies that this object version is a
			// delete marker
			readQuorum = N/2 + 1
		}