diff --git a/BasicSolver/3D-mpi-io/src/main.c b/BasicSolver/3D-mpi-io/src/main.c
index 231dec4..17fc72f 100644
--- a/BasicSolver/3D-mpi-io/src/main.c
+++ b/BasicSolver/3D-mpi-io/src/main.c
@@ -76,6 +76,7 @@ int main(int argc, char** argv)
         printf("Solution took %.2fs\n", timeStop - timeStart);
     }
 
+    // testInit(&solver);
     VtkOptions opts = { .grid = solver.grid, .comm = solver.comm };
     vtkOpen(&opts, solver.problem);
     vtkScalar(&opts, "pressure", solver.p);
diff --git a/BasicSolver/3D-mpi-io/src/test.c b/BasicSolver/3D-mpi-io/src/test.c
index 1665ce6..5f61b9f 100644
--- a/BasicSolver/3D-mpi-io/src/test.c
+++ b/BasicSolver/3D-mpi-io/src/test.c
@@ -26,10 +26,21 @@ void testInit(Solver* s)
     for (int k = 0; k < kmaxLocal + 2; k++) {
         for (int j = 0; j < jmaxLocal + 2; j++) {
             for (int i = 0; i < imaxLocal + 2; i++) {
-                G(p, i, j, k) = myrank;
-                G(f, i, j, k) = myrank;
-                G(g, i, j, k) = myrank;
-                G(h, i, j, k) = myrank;
+                G(p, i, j, k) = 10.0;
+                G(f, i, j, k) = myrank + 1.0;
+                G(g, i, j, k) = myrank + 1.0;
+                G(h, i, j, k) = myrank + 1.0;
+            }
+        }
+    }
+
+    for (int k = 1; k < kmaxLocal + 1; k++) {
+        for (int j = 1; j < jmaxLocal + 1; j++) {
+            for (int i = 1; i < imaxLocal + 1; i++) {
+                G(p, i, j, k) = myrank + 1.0;
+                G(f, i, j, k) = myrank + 1.0;
+                G(g, i, j, k) = myrank + 1.0;
+                G(h, i, j, k) = myrank + 1.0;
             }
         }
     }
diff --git a/BasicSolver/3D-mpi-io/src/vtkWriter.c b/BasicSolver/3D-mpi-io/src/vtkWriter.c
index 29b27f2..fe9dc3f 100644
--- a/BasicSolver/3D-mpi-io/src/vtkWriter.c
+++ b/BasicSolver/3D-mpi-io/src/vtkWriter.c
@@ -14,6 +14,16 @@
 #include "comm.h"
 #include "vtkWriter.h"
 
+static void resetFileview(VtkOptions* o)
+{
+    // reset fileview for output of string header
+    MPI_Offset disp;
+    MPI_Barrier(o->comm.comm);
+    MPI_File_get_size(o->fh, &disp);
+    MPI_File_set_view(o->fh, disp, MPI_CHAR, MPI_CHAR, "native", MPI_INFO_NULL);
+    // printf("Rank %d disp %lld\n", o->comm.rank, disp);
+}
+
 static void writeHeader(VtkOptions* o)
 {
     const size_t MAX_HEADER = 200;
@@ -42,10 +52,9 @@ static void writeHeader(VtkOptions* o)
         o->grid.imax * o->grid.jmax * o->grid.kmax);
 
     if (commIsMaster(&o->comm)) {
-        MPI_File_write_at(o->fh, 0, header, strlen(header), MPI_CHAR, MPI_STATUS_IGNORE);
+        MPI_File_write(o->fh, header, strlen(header), MPI_CHAR, MPI_STATUS_IGNORE);
     }
 
-    o->disp = strlen(header);
     free(header);
 }
 
@@ -57,22 +66,16 @@ void vtkOpen(VtkOptions* o, char* problem)
     snprintf(filename, 50, "%s-p%d.vtk", problem, o->comm.size);
     MPI_File_open(o->comm.comm,
         filename,
-        MPI_MODE_WRONLY | MPI_MODE_CREATE,
+        MPI_MODE_WRONLY | MPI_MODE_CREATE | MPI_MODE_EXCL,
         MPI_INFO_NULL,
         &o->fh);
 
     if (commIsMaster(&o->comm)) {
         printf("Writing VTK output for %s\n", problem);
     }
-    writeHeader(o);
-}
 
-static void resetFileview(VtkOptions* o)
-{
-    // reset fileview for output of string header
-    MPI_Offset disp;
-    MPI_File_get_size(o->fh, &disp);
-    MPI_File_set_view(o->fh, disp, MPI_CHAR, MPI_CHAR, "native", MPI_INFO_NULL);
+    resetFileview(o);
+    writeHeader(o);
 }
 
 void vtkScalar(VtkOptions* o, char* name, double* s)
@@ -85,7 +88,7 @@ void vtkScalar(VtkOptions* o, char* name, double* s)
     char* header = (char*)malloc(MAX_HEADER);
     char* cursor = header;
 
-    cursor += sprintf(cursor, "SCALARS %s float 1\n", name);
+    cursor += sprintf(cursor, "SCALARS %s double 1\n", name);
     cursor += sprintf(cursor, "LOOKUP_TABLE default\n");
 
     if (commIsMaster(&o->comm)) {
@@ -100,6 +103,7 @@ void vtkScalar(VtkOptions* o, char* name, double* s)
     // set global view in file
     MPI_Offset disp;
     MPI_Datatype fileViewType;
+    MPI_Barrier(o->comm.comm);
     MPI_File_get_size(o->fh, &disp);
 
     MPI_Type_create_subarray(NDIMS,
@@ -112,6 +116,18 @@ void vtkScalar(VtkOptions* o, char* name, double* s)
     MPI_Type_commit(&fileViewType);
     MPI_File_set_view(o->fh, disp, MPI_DOUBLE, fileViewType, "external32", MPI_INFO_NULL);
 
+#ifdef VERBOSE
+    printf("Rank: %d, Disp: %lld,  Size(k,j,i): %d %d %d, Offset(k,j,i): %d %d %d\n",
+        o->comm.rank,
+        disp,
+        o->comm.kmaxLocal,
+        o->comm.jmaxLocal,
+        o->comm.imaxLocal,
+        offsets[KDIM],
+        offsets[JDIM],
+        offsets[IDIM]);
+#endif
+
     // create local bulk type
     MPI_Datatype bulkType;
 
@@ -152,7 +168,7 @@ void vtkVector(VtkOptions* o, char* name, VtkVector vec)
     const size_t MAX_HEADER = 100;
 
     char* header = (char*)malloc(MAX_HEADER);
-    sprintf(header, "VECTORS %s float\n", name);
+    sprintf(header, "VECTORS %s double\n", name);
 
     resetFileview(o);
     if (commIsMaster(&o->comm)) {
@@ -164,21 +180,25 @@ void vtkVector(VtkOptions* o, char* name, VtkVector vec)
 
     // set global view in file
     MPI_Offset disp;
-    MPI_Datatype fileViewType;
+    MPI_Datatype fileViewType, vectorType;
+    MPI_Barrier(o->comm.comm);
     MPI_File_get_size(o->fh, &disp);
 
-    MPI_Type_create_subarray(NDIMS + 1,
-        (int[NDIMS + 1]) { o->grid.kmax, o->grid.jmax, o->grid.imax, NDIMS },
-        (int[NDIMS + 1]) { kmaxLocal, jmaxLocal, imaxLocal, NDIMS },
+    MPI_Type_contiguous(NDIMS, MPI_DOUBLE, &vectorType);
+    MPI_Type_commit(&vectorType);
+
+    MPI_Type_create_subarray(NDIMS,
+        (int[NDIMS]) { o->grid.kmax, o->grid.jmax, o->grid.imax },
+        (int[NDIMS]) { kmaxLocal, jmaxLocal, imaxLocal },
         offsets,
         MPI_ORDER_C,
-        MPI_DOUBLE,
+        vectorType,
         &fileViewType);
     MPI_Type_commit(&fileViewType);
     MPI_File_set_view(o->fh, disp, MPI_DOUBLE, fileViewType, "external32", MPI_INFO_NULL);
 
-    size_t cnt  = imaxLocal * jmaxLocal * kmaxLocal * NDIMS;
-    double* tmp = allocate(64, cnt * sizeof(double));
+    size_t cnt  = imaxLocal * jmaxLocal * kmaxLocal;
+    double* tmp = allocate(64, cnt * NDIMS * sizeof(double));
     int idx     = 0;
 
     for (int k = 1; k < kmaxLocal + 1; k++) {
@@ -191,8 +211,10 @@ void vtkVector(VtkOptions* o, char* name, VtkVector vec)
         }
     }
 
-    MPI_File_write(o->fh, tmp, cnt, MPI_DOUBLE, MPI_STATUS_IGNORE);
+    if (commIsMaster(&o->comm)) printf("Write %d vectors\n", (int)cnt);
+    MPI_File_write(o->fh, tmp, cnt, vectorType, MPI_STATUS_IGNORE);
     MPI_Type_free(&fileViewType);
+    MPI_Type_free(&vectorType);
 
     // Binary segment must be terminated with newline character
     resetFileview(o);
diff --git a/BasicSolver/3D-mpi/config.mk b/BasicSolver/3D-mpi/config.mk
index 88fec3f..af5f1a0 100644
--- a/BasicSolver/3D-mpi/config.mk
+++ b/BasicSolver/3D-mpi/config.mk
@@ -1,5 +1,5 @@
 # Supported: GCC, CLANG, ICC
-TAG ?= ICC
+TAG ?= CLANG
 ENABLE_OPENMP ?= false
 
 #Feature options
diff --git a/BasicSolver/3D-mpi/src/vtkWriter.c b/BasicSolver/3D-mpi/src/vtkWriter.c
index 5b4d36b..e96e773 100644
--- a/BasicSolver/3D-mpi/src/vtkWriter.c
+++ b/BasicSolver/3D-mpi/src/vtkWriter.c
@@ -11,18 +11,22 @@
 #include "vtkWriter.h"
 #define G(v, i, j, k) v[(k)*imax * jmax + (j)*imax + (i)]
 
-static float floatSwap(float f)
+static double floatSwap(double f)
 {
     union {
-        float f;
-        char b[4];
+        double f;
+        char b[8];
     } dat1, dat2;
 
     dat1.f    = f;
-    dat2.b[0] = dat1.b[3];
-    dat2.b[1] = dat1.b[2];
-    dat2.b[2] = dat1.b[1];
-    dat2.b[3] = dat1.b[0];
+    dat2.b[0] = dat1.b[7];
+    dat2.b[1] = dat1.b[6];
+    dat2.b[2] = dat1.b[5];
+    dat2.b[3] = dat1.b[4];
+    dat2.b[4] = dat1.b[3];
+    dat2.b[5] = dat1.b[2];
+    dat2.b[6] = dat1.b[1];
+    dat2.b[7] = dat1.b[0];
     return dat2.f;
 }
 
@@ -75,8 +79,8 @@ static void writeScalar(VtkOptions* o, double* s)
                 if (o->fmt == ASCII) {
                     fprintf(o->fh, "%f\n", G(s, i, j, k));
                 } else if (o->fmt == BINARY) {
-                    fwrite((float[1]) { floatSwap(G(s, i, j, k)) },
-                        sizeof(float),
+                    fwrite((double[1]) { floatSwap(G(s, i, j, k)) },
+                        sizeof(double),
                         1,
                         o->fh);
                 }
@@ -102,7 +106,7 @@ void vtkScalar(VtkOptions* o, char* name, double* s)
     if (o->mode == UNIX) {
         if (commIsMaster(&o->comm)) {
             if (!isInitialized(o->fh)) return;
-            fprintf(o->fh, "SCALARS %s float 1\n", name);
+            fprintf(o->fh, "SCALARS %s double 1\n", name);
             fprintf(o->fh, "LOOKUP_TABLE default\n");
             writeScalar(o, s);
         }
@@ -126,10 +130,10 @@ static void writeVector(VtkOptions* o, VtkVector vec)
                         G(vec.v, i, j, k),
                         G(vec.w, i, j, k));
                 } else if (o->fmt == BINARY) {
-                    fwrite((float[3]) { floatSwap(G(vec.u, i, j, k)),
+                    fwrite((double[3]) { floatSwap(G(vec.u, i, j, k)),
                                floatSwap(G(vec.v, i, j, k)),
                                floatSwap(G(vec.w, i, j, k)) },
-                        sizeof(float),
+                        sizeof(double),
                         3,
                         o->fh);
                 }
@@ -146,7 +150,7 @@ void vtkVector(VtkOptions* o, char* name, VtkVector vec)
     if (o->mode == UNIX) {
         if (commIsMaster(&o->comm)) {
             if (!isInitialized(o->fh)) return;
-            fprintf(o->fh, "VECTORS %s float\n", name);
+            fprintf(o->fh, "VECTORS %s double\n", name);
             writeVector(o, vec);
         }
     } else if (o->mode == MPI) {