### 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)

# 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) |
|--------:|------------------:|------------:|------------------------:|------------------------------:|-------------------------------:|

	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.

)

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 {

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))
}

//msgp:clearomitted

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

// A xlMetaV1Object represents `xl.meta` metadata header.

of common SLA here original cluster had 1024 drives with 16 drives per erasure set with default parity of '4', second pool is expected to have a minimum of 8 drives per erasure set to match the original cluster SLA (parity count) of '4'. '12' drives stripe per erasure set in the second pool satisfies the original pool's parity count.

Refer to the sizing guide with details on the default parity count chosen for different erasure stripe sizes [here](https://github.com/minio/minio/blob/mas...

import (
	"encoding/json"
	"log"
	"os"
	"path/filepath"

	"github.com/klauspost/compress/zip"
	"github.com/minio/cli"
)

var fmtGenFlags = []cli.Flag{
	cli.IntFlag{
		Name:  "parity",
		Usage: "specify erasure code parity",
	},
	cli.StringFlag{
		Name:  "deployment-id",
		Usage: "deployment-id of the MinIO cluster for which format.json is needed",
	},
	cli.StringFlag{
		Name:   "address",

func erasureSelfTest() {
	// Approx runtime ~1ms
	var testConfigs [][2]uint8
	for total := uint8(4); total < 16; total++ {
		for data := total / 2; data < total; data++ {
			parity := total - data
			testConfigs = append(testConfigs, [2]uint8{data, parity})
		}
	}
	got := make(map[[2]uint8]map[ErasureAlgo]uint64, len(testConfigs))
	// Copied from output of fmt.Printf("%#v", got) at the end.

		t.Fatalf("Unable to format drives for erasure, %s", err)
	}

	ep := PoolEndpoints{Endpoints: endpoints}

	parity, err := ecDrivesNoConfig(16)
	if err != nil {
		t.Fatalf("Unexpected error during EC drive config: %v", err)
	}
	if _, err := newErasureSets(ctx, ep, storageDisks, format, parity, 0); err != nil {
		t.Fatalf("Unable to initialize erasure")
	}
}