update dsync implementation to fix a regression (#5513)

Currently minio master requires 4 servers, we
have decided to run on a minimum of 2 servers
instead - fixes a regression from previous
releases where 3 server setups were supported.

cmd/endpoint_test.go

@@ -108,7 +108,7 @@ func TestNewEndpointList(t *testing.T) {
 		{[]string{"d1", "d2", "d3", "d1"}, fmt.Errorf("duplicate endpoints found")},
 		{[]string{"d1", "d2", "d3", "./d1"}, fmt.Errorf("duplicate endpoints found")},
 		{[]string{"http://localhost/d1", "http://localhost/d2", "http://localhost/d1", "http://localhost/d4"}, fmt.Errorf("duplicate endpoints found")},
-		{[]string{"d1", "d2", "d3", "d4", "d5"}, fmt.Errorf("A total of 5 endpoints were found. For erasure mode it should be an even number between 4 and 16")},
+		{[]string{"d1", "d2", "d3", "d4", "d5"}, fmt.Errorf("A total of 5 endpoints were found. For erasure mode it should be an even number between 4 and 32")},
 		{[]string{"ftp://server/d1", "http://server/d2", "http://server/d3", "http://server/d4"}, fmt.Errorf("'ftp://server/d1': invalid URL endpoint format")},
 		{[]string{"d1", "http://localhost/d2", "d3", "d4"}, fmt.Errorf("mixed style endpoints are not supported")},
 		{[]string{"http://example.org/d1", "https://example.com/d1", "http://example.net/d1", "https://example.edut/d1"}, fmt.Errorf("mixed scheme is not supported")},

cmd/xl-v1.go

@@ -1,5 +1,5 @@
 /*
- * Minio Cloud Storage, (C) 2016 Minio, Inc.
+ * Minio Cloud Storage, (C) 2016, 2017, 2018 Minio, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -35,7 +35,7 @@ const (
 	uploadsJSONFile = "uploads.json"
 
 	// Maximum erasure blocks.
-	maxErasureBlocks = 16
+	maxErasureBlocks = 32
 
 	// Minimum erasure blocks.
 	minErasureBlocks = 4
@@ -51,6 +51,7 @@ type xlObjects struct {
 
 	// name space mutex for object layer
 	nsMutex *nsLockMap
+
 	// Variable represents bucket policies in memory.
 	bucketPolicies *bucketPolicies
 }

vendor/github.com/minio/dsync/dsync.go

@@ -18,6 +18,7 @@ package dsync
 
 import (
 	"errors"
+	"math"
 )
 
 // Dsync represents dsync client object which is initialized with
@@ -41,12 +42,10 @@ type Dsync struct {
 
 // New - initializes a new dsync object with input rpcClnts.
 func New(rpcClnts []NetLocker, rpcOwnNode int) (*Dsync, error) {
-	if len(rpcClnts) < 4 {
+	if len(rpcClnts) < 2 {
-		return nil, errors.New("Dsync is not designed for less than 4 nodes")
+		return nil, errors.New("Dsync is not designed for less than 2 nodes")
-	} else if len(rpcClnts) > 16 {
+	} else if len(rpcClnts) > 32 {
-		return nil, errors.New("Dsync is not designed for more than 16 nodes")
+		return nil, errors.New("Dsync is not designed for more than 32 nodes")
-	} else if len(rpcClnts)%2 != 0 {
-		return nil, errors.New("Dsync is not designed for an uneven number of nodes")
 	}
 
 	if rpcOwnNode > len(rpcClnts) {
@@ -55,8 +54,10 @@ func New(rpcClnts []NetLocker, rpcOwnNode int) (*Dsync, error) {
 
 	ds := &Dsync{}
 	ds.dNodeCount = len(rpcClnts)
-	ds.dquorum = ds.dNodeCount/2 + 1
+
-	ds.dquorumReads = ds.dNodeCount / 2
+	// With odd number of nodes, write and read quorum is basically the same
+	ds.dquorum = int(ds.dNodeCount/2) + 1
+	ds.dquorumReads = int(math.Ceil(float64(ds.dNodeCount) / 2.0))
 	ds.ownNode = rpcOwnNode
 
 	// Initialize node name and rpc path for each NetLocker object.

vendor/vendor.json

@@ -380,10 +380,10 @@
 			"revisionTime": "2017-02-27T07:32:28Z"
 		},
 		{
-			"checksumSHA1": "qhWQM7xmqaxFqADNTj8YPjE/8Ws=",
+			"checksumSHA1": "1AQVDkFvVxn1RMTLyjeDSESBhrc=",
 			"path": "github.com/minio/dsync",
-			"revision": "ed0989bc6c7b199f749fa6be0b7ee98d689b88c7",
+			"revision": "439a0961af700f80db84cc180fe324a89070fa65",
-			"revisionTime": "2017-11-22T09:16:00Z"
+			"revisionTime": "2018-01-23T12:12:34Z"
 		},
 		{
 			"path": "github.com/minio/go-homedir",