feat: allow retaining parity SLA to be configurable (#19260)

at scale customers might start with failed drives,
causing skew in the overall usage ratio per EC set.

make this configurable such that customers can turn
this off as needed depending on how comfortable they
are.

cmd/erasure-object.go

@@ -1297,25 +1297,21 @@ func (er erasureObjects) putObject(ctx context.Context, bucket string, object st
 
 	storageDisks := er.getDisks()
 
-	parityDrives := len(storageDisks) / 2
-	if !opts.MaxParity {
-		// Get parity and data drive count based on storage class metadata
-		parityDrives = globalStorageClass.GetParityForSC(userDefined[xhttp.AmzStorageClass])
-		if parityDrives < 0 {
-			parityDrives = er.defaultParityCount
-		}
-
+	// Get parity and data drive count based on storage class metadata
+	parityDrives := globalStorageClass.GetParityForSC(userDefined[xhttp.AmzStorageClass])
+	if parityDrives < 0 {
+		parityDrives = er.defaultParityCount
+	}
+	if opts.MaxParity {
+		parityDrives = len(storageDisks) / 2
+	}
+	if !opts.MaxParity && globalStorageClass.AvailabilityOptimized() {
 		// If we have offline disks upgrade the number of erasure codes for this object.
 		parityOrig := parityDrives
 
 		var offlineDrives int
 		for _, disk := range storageDisks {
-			if disk == nil {
-				parityDrives++
-				offlineDrives++
-				continue
-			}
-			if !disk.IsOnline() {
+			if disk == nil || !disk.IsOnline() {
 				parityDrives++
 				offlineDrives++
 				continue