diff --git a/core/src/commonMain/kotlin/com/sunya/netchdf/hdf5/H5cdmBuilder.kt b/core/src/commonMain/kotlin/com/sunya/netchdf/hdf5/H5cdmBuilder.kt
index dd3131bd..e38fa22b 100644
--- a/core/src/commonMain/kotlin/com/sunya/netchdf/hdf5/H5cdmBuilder.kt
+++ b/core/src/commonMain/kotlin/com/sunya/netchdf/hdf5/H5cdmBuilder.kt
@@ -185,7 +185,6 @@ internal open class DataContainerAttribute(
 
 val mdlClassCount = getDataLayoutCounts()
 
-// TODO ?? none of the version4 layouts are implemented
 internal class DataContainerVariable(
     override val name: String,
     override val h5type: H5TypeInfo,
diff --git a/core/src/commonMain/kotlin/com/sunya/netchdf/hdf5/Hdf5File.kt b/core/src/commonMain/kotlin/com/sunya/netchdf/hdf5/Hdf5File.kt
index 4adf7a5d..1cd01aa1 100644
--- a/core/src/commonMain/kotlin/com/sunya/netchdf/hdf5/Hdf5File.kt
+++ b/core/src/commonMain/kotlin/com/sunya/netchdf/hdf5/Hdf5File.kt
@@ -31,6 +31,11 @@ class Hdf5File(val filename : String, strict : Boolean = false) : Netchdf {
     override fun type() = header.formatType()
     override val size : Long get() = raf.size()
 
+    fun layoutName(v: Variable<*>): String {
+        val vinfo = (v.spObject as DataContainerVariable)
+        return if (vinfo.mdl != null) vinfo.mdl.javaClass.simpleName else "none"
+    }
+
     override fun <T> readArrayData(v2: Variable<T>, section: SectionPartial?): ArrayTyped<T> {
         if (v2.nelems == 0L) {
             return ArrayEmpty(v2.shape.toIntArray(), v2.datatype)
diff --git a/core/src/commonTest/data/netcdf4/ds.mint.nc b/core/src/commonTest/data/netcdf4/ds.mint.nc
new file mode 100755
index 00000000..beeba6bd
Binary files /dev/null and b/core/src/commonTest/data/netcdf4/ds.mint.nc differ
diff --git a/core/src/commonTest/kotlin/com/sunya/netchdf/hdf5/Btree1extTest.kt b/core/src/commonTest/kotlin/com/sunya/netchdf/hdf5/Btree1extTest.kt
index 974fc46d..494e6267 100644
--- a/core/src/commonTest/kotlin/com/sunya/netchdf/hdf5/Btree1extTest.kt
+++ b/core/src/commonTest/kotlin/com/sunya/netchdf/hdf5/Btree1extTest.kt
@@ -2,27 +2,30 @@
 
 package com.sunya.netchdf.hdf5
 
-import com.sunya.cdm.api.computeSize
+import com.sunya.cdm.api.ArraySection
 import com.sunya.cdm.api.toLongArray
 import com.sunya.cdm.iosp.OkioFile
 import com.sunya.cdm.iosp.OpenFileIF
-import com.sunya.cdm.layout.Tiling
 import com.sunya.cdm.util.InternalLibraryApi
+import com.sunya.netchdf.testutil.nano
+import com.sunya.netchdf.testutil.testData
+import kotlin.system.measureNanoTime
 import kotlin.test.Test
 
 class Btree1extTest {
 
+    // 227322 == /home/all/testdata/cdmUnitTest/formats/netcdf4/ds.mint.nc#Minimum_temperature_surface_12_Hour_Minimum#DataLayoutBTreeVer1 } files
+
     @Test
     fun testBTree1ext() {
-        val filename = "/home/all/testdata/cdmUnitTest/formats/netcdf4/hiig_forec_20140208.nc"
-        val varname = "salt"
+        val filename = testData + "netcdf4/ds.mint.nc"
+        val varname = "Minimum_temperature_surface_12_Hour_Minimum"
         Hdf5File(filename).use { myfile ->
             println("${myfile.type()} $filename ${myfile.size / 1000.0 / 1000.0} Mbytes")
-            // println(myfile.cdl())
+            println(myfile.cdl())
 
             val h5 = myfile.header
 
-            var countChunks = 0
             val myvar = myfile.rootGroup().allVariables().find { it.fullname() == varname }
                 ?: throw RuntimeException("cant find $varname")
 
@@ -36,18 +39,11 @@ class Btree1extTest {
 
             require(myvar.spObject is DataContainerVariable)
             val vinfo = myvar.spObject
-            require(vinfo.mdl is DataLayoutBTreeVer1)
+            require(vinfo.mdl is DataLayoutBTreeVer1) {"must use DataLayoutBTreeVer1"}
             val mdl = vinfo.mdl
             val chunkShape = mdl.chunkDims
-            val tiling = Tiling(varShape, chunkShape.toLongArray())
-            val nchunks = tiling.tileShape.computeSize()
 
             // a thread-safe accessor of the btree
-            //     val raf: OpenFileExtended,
-            //    val rootNodeAddress: Long,
-            //    val nodeType : Int,  // 0 = group/symbol table, 1 = raw data chunks
-            //    varShape: LongArray,
-            //    chunkShape: LongArray,
             val bTreeExt = BTree1ext(rafext, mdl.btreeAddress, 1, varShape, chunkShape.toLongArray())
             val rootNode = bTreeExt.rootNode()
 
@@ -55,4 +51,28 @@ class Btree1extTest {
         }
     }
 
+    @Test
+    fun testH5readConcurrent() {
+        val filename = testData + "netcdf4/ds.mint.nc"
+        val varname = "Minimum_temperature_surface_12_Hour_Minimum"
+        Hdf5File(filename).use { myfile ->
+            println("${myfile.type()} $filename ${myfile.size / 1000.0 / 1000.0} Mbytes")
+
+            val myvar = myfile.rootGroup().allVariables().find { it.fullname() == varname }
+                ?: throw RuntimeException("cant find $varname")
+
+            println("nthreads,   time in secs")
+
+            for (nthreads in listOf(1, 2, 4, 8, 10, 16, 20, 24, 32, 40, 48)) {
+                val time = measureNanoTime {
+                    val reader = H5readConcurrent(myfile, myvar)
+                    reader.readChunks(nthreads) { asect: ArraySection<*> ->
+                        // println(" section = ${asect.section}")
+                    }
+                }
+                println("$nthreads, ${time * nano}")
+            }
+        }
+    }
+
 }
diff --git a/core/src/commonTest/kotlin/com/sunya/netchdf/testutil/ReadCommon.kt b/core/src/commonTest/kotlin/com/sunya/netchdf/testutil/ReadCommon.kt
index 6a6ea341..a18cfb46 100644
--- a/core/src/commonTest/kotlin/com/sunya/netchdf/testutil/ReadCommon.kt
+++ b/core/src/commonTest/kotlin/com/sunya/netchdf/testutil/ReadCommon.kt
@@ -8,6 +8,8 @@ import kotlin.test.assertTrue
 
 //////////////////////////////////////////////////////////////////////////////////////////////////////
 
+const val nano = 1.0e-9
+
 fun showNetchdfHeader(filename: String) {
     println(filename)
     openNetchdfFile(filename).use { myfile ->
diff --git a/testfiles/src/test/kotlin/com/sunya/netchdf/CountVersions.kt b/testfiles/src/test/kotlin/com/sunya/netchdf/CountVersions.kt
index 5feafab5..10739aa0 100644
--- a/testfiles/src/test/kotlin/com/sunya/netchdf/CountVersions.kt
+++ b/testfiles/src/test/kotlin/com/sunya/netchdf/CountVersions.kt
@@ -1,5 +1,6 @@
 package com.sunya.netchdf
 
+import com.sunya.netchdf.hdf5.Hdf5File
 import com.sunya.netchdf.testfiles.H4Files
 import com.sunya.netchdf.testfiles.H5Files
 import com.sunya.netchdf.testfiles.JhdfFiles
@@ -112,8 +113,13 @@ class CountVersions {
                     if (ncfile == null) {
                         println("Not a netchdf file=$filename ")
                     } else {
+                        val hdf5File = if (ncfile.type() in listOf("netcdf4", "hdf")) {
+                            ncfile as Hdf5File
+                        } else null
+
                         ncfile.rootGroup().allVariables().forEach { v ->
-                            varSizes["$filename#${v.name}" ] = v.nelems
+                            val layout = hdf5File?.layoutName(v) ?: ""
+                            varSizes["$filename#${v.name}#$layout"] = v.nelems
                         }
                     }
                 }
diff --git a/testfiles/src/test/kotlin/com/sunya/netchdf/hdf5/H5readConcurrentTest.kt b/testfiles/src/test/kotlin/com/sunya/netchdf/hdf5/H5readConcurrentTest.kt
index 6dcbcabe..025ee945 100644
--- a/testfiles/src/test/kotlin/com/sunya/netchdf/hdf5/H5readConcurrentTest.kt
+++ b/testfiles/src/test/kotlin/com/sunya/netchdf/hdf5/H5readConcurrentTest.kt
@@ -45,7 +45,6 @@ class H5readConcurrentTest {
         }
     }
 
-
     @Test
     fun testH5readConcurrent() {
         val filename = "/home/all/testdata/cdmUnitTest/formats/netcdf4/hiig_forec_20140208.nc"