XL/Erasure: Blocksize for object-part should be derived from what was decided during xl.NewMultipartUpload which creates xl.json. (#1920)

fixes #1919

erasure-createfile.go

@@ -29,13 +29,13 @@ import (
 // all the disks, writes also calculate individual block's checksum
 // for future bit-rot protection.
 func erasureCreateFile(disks []StorageAPI, volume string, path string, partName string, data io.Reader, eInfos []erasureInfo, writeQuorum int) (newEInfos []erasureInfo, size int64, err error) {
-	// Allocated blockSized buffer for reading.
-	buf := make([]byte, blockSizeV1)
-	hashWriters := newHashWriters(len(disks))
-
 	// Just pick one eInfo.
 	eInfo := pickValidErasureInfo(eInfos)
 
+	// Allocated blockSized buffer for reading.
+	buf := make([]byte, eInfo.BlockSize)
+	hashWriters := newHashWriters(len(disks))
+
 	// Read until io.EOF, erasure codes data and writes to all disks.
 	for {
 		var n int