Support variable server pools (#11256)

Current implementation requires server pools to have
same erasure stripe sizes, to facilitate same SLA
and expectations.

This PR allows server pools to be variadic, i.e they
do not have to be same erasure stripe sizes - instead
they should have SLA for parity ratio.

If the parity ratio cannot be guaranteed by the new
server pool, the deployment is rejected i.e server
pool expansion is not allowed.

cmd/erasure-sets.go

@@ -81,6 +81,7 @@ type erasureSets struct {
 
 	// Total number of sets and the number of disks per set.
 	setCount, setDriveCount int
+	defaultParityCount      int
 
 	disksConnectEvent chan diskConnectInfo
 
@@ -355,21 +356,36 @@ func newErasureSets(ctx context.Context, endpoints Endpoints, storageDisks []Sto
 
 	endpointStrings := make([]string, len(endpoints))
 
+	// If storage class is not set during startup, default values are used
+	// -- Default for Reduced Redundancy Storage class is, parity = 2
+	// -- Default for Standard Storage class is, parity = 2 - disks 4, 5
+	// -- Default for Standard Storage class is, parity = 3 - disks 6, 7
+	// -- Default for Standard Storage class is, parity = 4 - disks 8 to 16
+	var defaultParityCount int
+
+	switch format.Erasure.DistributionAlgo {
+	case formatErasureVersionV3DistributionAlgoV3:
+		defaultParityCount = getDefaultParityBlocks(setDriveCount)
+	default:
+		defaultParityCount = setDriveCount / 2
+	}
+
 	// Initialize the erasure sets instance.
 	s := &erasureSets{
-		sets:              make([]*erasureObjects, setCount),
-		erasureDisks:      make([][]StorageAPI, setCount),
-		erasureLockers:    make([][]dsync.NetLocker, setCount),
-		erasureLockOwner:  GetLocalPeer(globalEndpoints),
-		endpoints:         endpoints,
-		endpointStrings:   endpointStrings,
-		setCount:          setCount,
-		setDriveCount:     setDriveCount,
-		format:            format,
-		disksConnectEvent: make(chan diskConnectInfo),
-		distributionAlgo:  format.Erasure.DistributionAlgo,
-		deploymentID:      uuid.MustParse(format.ID),
-		mrfOperations:     make(map[healSource]int),
+		sets:               make([]*erasureObjects, setCount),
+		erasureDisks:       make([][]StorageAPI, setCount),
+		erasureLockers:     make([][]dsync.NetLocker, setCount),
+		erasureLockOwner:   GetLocalPeer(globalEndpoints),
+		endpoints:          endpoints,
+		endpointStrings:    endpointStrings,
+		setCount:           setCount,
+		setDriveCount:      setDriveCount,
+		defaultParityCount: defaultParityCount,
+		format:             format,
+		disksConnectEvent:  make(chan diskConnectInfo),
+		distributionAlgo:   format.Erasure.DistributionAlgo,
+		deploymentID:       uuid.MustParse(format.ID),
+		mrfOperations:      make(map[healSource]int),
 	}
 
 	mutex := newNSLock(globalIsDistErasure)
@@ -416,13 +432,14 @@ func newErasureSets(ctx context.Context, endpoints Endpoints, storageDisks []Sto
 
 		// Initialize erasure objects for a given set.
 		s.sets[i] = &erasureObjects{
-			setDriveCount: setDriveCount,
-			getDisks:      s.GetDisks(i),
-			getLockers:    s.GetLockers(i),
-			getEndpoints:  s.GetEndpoints(i),
-			nsMutex:       mutex,
-			bp:            bp,
-			mrfOpCh:       make(chan partialOperation, 10000),
+			setDriveCount:      setDriveCount,
+			defaultParityCount: defaultParityCount,
+			getDisks:           s.GetDisks(i),
+			getLockers:         s.GetLockers(i),
+			getEndpoints:       s.GetEndpoints(i),
+			nsMutex:            mutex,
+			bp:                 bp,
+			mrfOpCh:            make(chan partialOperation, 10000),
 		}
 	}
 
@@ -466,6 +483,12 @@ func (s *erasureSets) SetDriveCount() int {
 	return s.setDriveCount
 }
 
+// ParityCount returns the default parity count used while erasure
+// coding objects
+func (s *erasureSets) ParityCount() int {
+	return s.defaultParityCount
+}
+
 // StorageUsageInfo - combines output of StorageInfo across all erasure coded object sets.
 // This only returns disk usage info for ServerPools to perform placement decision, this call
 // is not implemented in Object interface and is not meant to be used by other object
@@ -616,9 +639,9 @@ func crcHashMod(key string, cardinality int) int {
 
 func hashKey(algo string, key string, cardinality int, id [16]byte) int {
 	switch algo {
-	case formatErasureVersionV2DistributionAlgoLegacy:
+	case formatErasureVersionV2DistributionAlgoV1:
 		return crcHashMod(key, cardinality)
-	case formatErasureVersionV3DistributionAlgo:
+	case formatErasureVersionV3DistributionAlgoV2, formatErasureVersionV3DistributionAlgoV3:
 		return sipHashMod(key, cardinality, id)
 	default:
 		// Unknown algorithm returns -1, also if cardinality is lesser than 0.